Bio

Bio


Wandell's research includes image system engineering and visual neuroscience. In cooperation with Professor Emeritus Joseph Goodman (a faculty member in Stanford's School of Engineering), Professor Wandell founded the university's Image Systems Engineering Program. He is also co-principal investigator of the Programmable Digital Camera program, which is an industry-sponsored effort to develop programmable CMOS sensors. As part of this effort, Wandell and his team study and build devices used for digital imaging, including image sensors, high dynamic range displays, and software simulations of the digital imaging pipeline. Professor Wandell's work in visual neuroscience uses both functional MRI and behavior testing to understand the action of the visual portions of the brain. His team has developed a set of methods for identifying and measuring the signals in several visual areas within the human brain, including regions that respond powerful to motion and color. Recently, his team measured the reorganization of brain function during human development and following brain injury; they are now actively studying the development of visual signals during the age period in which children are learning to read.

Academic Appointments


Administrative Appointments


  • Director, Stanford's Center for Cognitive and Neurobiological Imaging (2010 - Present)
  • Chair, Psychology (2006 - 2009)

Honors & Awards


  • Member, US National Academy of Sciences (2003)
  • Macbeth Prize, Inter-Society Color Council (2000)
  • Edridge-Green Medal in Ophthalmology for work in visual neuroscience, Edridge-Green Medal in Ophthalmology for work in visual neuroscience (1997)
  • Senior Investigator, McKnight (1997)
  • Fellow, Optical Society of America (1990)
  • Troland Research Award, National Academy of Sciences (1986)
  • Member, American Academy of Arts and Sciences (2011)
  • Member, National Academy of Sciences (2003)

Boards, Advisory Committees, Professional Organizations


  • Member, National Academy of Sciences (2013 - Present)

Professional Education


  • PhD, UC Irvine, Social Sciences (1977)

Research & Scholarship

Current Research and Scholarly Interests


Visual perception

Professor Wandell's work in visual neuroscience uses both neuroimaging and behavior testing to understand the action of the visual portions of the brain. His team has developed a set of magnetic resonance imaging methods for identifying and measuring distinct and specialized regions of human visual cortex, including regions that respond powerful to motion and color. His team has been particularly interested in measuring the development of brain function and reorganization following injury or abnormal development.

Reading development

The Wandell lab is applying a powerful set of MRI measurement methodologies to study human brain development. These include diffusion measures, functional measures, and novel approaches for assessing quantitative tissue properties such as tissue volume and chemistry. In one group of studies, they are measuring the signals and growth of visual cortex in children, aged 8-12, during the period children become skilled readers. Using very high spatial resolution and neuroimaging techniques, including some methods developed by this group, the lab is hoping to understand how visual signals contribute to the neural pathways of reading. These measurements of the developmental changes during the acquisition of skilled reading are intended to explain how visual signals are rapidly identified and classified as we read.

Teaching

2013-14 Courses


Postdoctoral Advisees


Graduate and Fellowship Programs


Publications

Journal Articles


  • Asynchronous Broadband Signals Are the Principal Source of the BOLD Response in Human Visual Cortex CURRENT BIOLOGY Winawer, J., Kay, K. N., Foster, B. L., Rauschecker, A. M., Parvizi, J., Wandell, B. A. 2013; 23 (13): 1145-1153

    Abstract

    Activity in the living human brain can be studied using multiple methods, spanning a wide range of spatial and temporal resolutions. We investigated the relationship between electric field potentials measured with electrocorticography (ECoG) and the blood oxygen level-dependent (BOLD) response measured with functional magnetic resonance imaging (fMRI). We set out to explain the full set of measurements by modeling the underlying neural circuits.ECoG responses in visual cortex can be separated into two visually driven components. One component is a specific temporal response that follows each stimulus contrast reversal ("stimulus locked"); the other component is an increase in the response variance ("asynchronous"). For electrodes in visual cortex (V1, V2, V3), the two measures respond to stimuli in the same region of visual space, but they have different spatial summation properties. The stimulus-locked ECoG component sums contrast approximately linearly across space; spatial summation in the asynchronous ECoG component is subadditive. Spatial summation measured using BOLD closely matches the asynchronous component. We created a neural simulation that accurately captures the main features of the ECoG time series; in the simulation, the stimulus-locked and asynchronous components arise from different neural circuits.These observations suggest that the two ECoG components arise from different neural sources within the same cortical region. The spatial summation measurements and simulations suggest that the BOLD response arises primarily from neural sources that generate the asynchronous broadband ECoG component.

    View details for DOI 10.1016/j.cub.2013.05.001

    View details for Web of Science ID 000321605600015

    View details for PubMedID 23770184

  • Biological development of reading circuits. Current opinion in neurobiology Wandell, B. A., Yeatman, J. D. 2013; 23 (2): 261-268

    Abstract

    Human neuroimaging is expanding our understanding of the biological processes that are essential for healthy brain function. Methods such as diffusion weighted imaging provide insights into white matter fascicles, growth and pruning of dendritic arbors and axons, and properties of glia. This review focuses on what we have learned from diffusion imaging about these processes and the development of reading circuitry in the human brain. Understanding reading circuitry development may suggest ways to improve how we teach children to read.

    View details for DOI 10.1016/j.conb.2012.12.005

    View details for PubMedID 23312307

  • Human trichromacy revisited PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Horiguchi, H., Winawer, J., Dougherty, R. F., Wandell, B. A. 2013; 110 (3): E260-E269

    Abstract

    The presence of a photopigment (melanopsin) within certain retinal ganglion cells was a surprising and significant discovery. This pigment is routinely described as "nonvisual" to highlight its signaling role in pupil dilation and circadian rhythms. Here we asked whether light absorbed by melanopsin can be seen by healthy human subjects. To answer this requires delivering intense (above rod saturation), well-controlled lights using four independent primaries. We collected detection thresholds to many four-primary stimuli. Threshold measurements in the fovea are explained by trichromatic theory, with no need to invoke a fourth photopigment. In the periphery, where melanopsin is present, threshold measurements deviate from trichromatic theory; at high photopic levels, sensitivity is explained by absorptions in four, not three, photopigment classes. We consider a series of hypotheses to explain the tetrasensitivity at high photopic levels in the human peripheral field. The most likely hypothesis is that in healthy human subjects melanopsin absorptions influence visibility.

    View details for DOI 10.1073/pnas.1214240110

    View details for Web of Science ID 000313909100013

    View details for PubMedID 23256158

  • Development of white matter and reading skills PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yeatman, J. D., Dougherty, R. F., Ben-Shachar, M., Wandell, B. A. 2012; 109 (44): E3045-E3053

    Abstract

    White matter tissue properties are highly correlated with reading proficiency; we would like to have a model that relates the dynamics of an individual's white matter development to their acquisition of skilled reading. The development of cerebral white matter involves multiple biological processes, and the balance between these processes differs between individuals. Cross-sectional measures of white matter mask the interplay between these processes and their connection to an individual's cognitive development. Hence, we performed a longitudinal study to measure white-matter development (diffusion-weighted imaging) and reading development (behavioral testing) in individual children (age 7-15 y). The pattern of white-matter development differed significantly among children. In the left arcuate and left inferior longitudinal fasciculus, children with above-average reading skills initially had low fractional anisotropy (FA) that increased over the 3-y period, whereas children with below-average reading skills had higher initial FA that declined over time. We describe a dual-process model of white matter development comprising biological processes with opposing effects on FA, such as axonal myelination and pruning, to explain the pattern of results.

    View details for DOI 10.1073/pnas.1206792109

    View details for Web of Science ID 000311149900014

    View details for PubMedID 23045658

  • Learning to See Words ANNUAL REVIEW OF PSYCHOLOGY, VOL 63 Wandell, B. A., Rauschecker, A. M., Yeatman, J. D. 2012; 63: 31-53

    Abstract

    Skilled reading requires recognizing written words rapidly; functional neuroimaging research has clarified how the written word initiates a series of responses in visual cortex. These responses are communicated to circuits in ventral occipitotemporal (VOT) cortex that learn to identify words rapidly. Structural neuroimaging has further clarified aspects of the white matter pathways that communicate reading signals between VOT and language systems. We review this circuitry, its development, and its deficiencies in poor readers. This review emphasizes data that measure the cortical responses and white matter pathways in individual subjects rather than group differences. Such methods have the potential to clarify why a child has difficulty learning to read and to offer guidance about the interventions that may be useful for that child.

    View details for DOI 10.1146/annurev-psych-120710-100434

    View details for Web of Science ID 000299709900002

    View details for PubMedID 21801018

  • Plasticity and stability of visual field maps in adult primary visual cortex NATURE REVIEWS NEUROSCIENCE Wandell, B. A., Smirnakis, S. M. 2009; 10 (12): 873-884

    Abstract

    It is important to understand the balance between cortical plasticity and stability in various systems and across spatial scales in the adult brain. Here we review studies of adult plasticity in primary visual cortex (V1), which has a key role in distributing visual information. There are claims of plasticity at multiple spatial scales in adult V1, but a number of inconsistencies in the supporting data raise questions about the extent and nature of such plasticity. Our understanding of the extent of plasticity in V1 is further limited by a lack of quantitative models to guide the interpretation of the data. These problems limit efforts to translate research findings about adult cortical plasticity into significant clinical, educational and policy applications.

    View details for DOI 10.1038/nrn2741

    View details for Web of Science ID 000271962500012

    View details for PubMedID 19904279

  • Visual field maps in human cortex NEURON Wandell, B. A., Dumoulin, S. O., Brewer, A. A. 2007; 56 (2): 366-383

    Abstract

    Much of the visual cortex is organized into visual field maps: nearby neurons have receptive fields at nearby locations in the image. Mammalian species generally have multiple visual field maps with each species having similar, but not identical, maps. The introduction of functional magnetic resonance imaging made it possible to identify visual field maps in human cortex, including several near (1) medial occipital (V1,V2,V3), (2) lateral occipital (LO-1,LO-2, hMT+), (3) ventral occipital (hV4, VO-1, VO-2), (4) dorsal occipital (V3A, V3B), and (5) posterior parietal cortex (IPS-0 to IPS-4). Evidence is accumulating for additional maps, including some in the frontal lobe. Cortical maps are arranged into clusters in which several maps have parallel eccentricity representations, while the angular representations within a cluster alternate in visual field sign. Visual field maps have been linked to functional and perceptual properties of the visual system at various spatial scales, ranging from the level of individual maps to map clusters to dorsal-ventral streams. We survey recent measurements of human visual field maps, describe hypotheses about the function and relationships between maps, and consider methods to improve map measurements and characterize the response properties of neurons comprising these maps.

    View details for DOI 10.1016/j.neuron.2007.10.012

    View details for Web of Science ID 000250740700013

    View details for PubMedID 17964252

  • White matter pathways in reading CURRENT OPINION IN NEUROBIOLOGY Ben-Shachar, M., Dougherty, R. F., Wandell, B. A. 2007; 17 (2): 258-270

    Abstract

    Skilled reading requires mapping of visual text to sound and meaning. Because reading relies on neural systems spread across the brain, a full understanding of this cognitive ability involves the identification of pathways that communicate information between these processing regions. In the past few years, diffusion tensor imaging has been used to identify correlations between white matter properties and reading skills in adults and children. White matter differences have been found in left temporo-parietal areas and in posterior callosal tracts. We review these findings and relate them to possible pathways that are important for various aspects of reading. We describe how the results from diffusion tensor imaging can be integrated with functional results in good and poor readers.

    View details for DOI 10.1016/j.conb.2007.03.006

    View details for Web of Science ID 000246324300018

    View details for PubMedID 17379499

  • Compressive spatial summation in human visual cortex JOURNAL OF NEUROPHYSIOLOGY Kay, K. N., Winawer, J., Mezer, A., Wandell, B. A. 2013; 110 (2): 481-494

    Abstract

    Neurons within a small (few mm(3)) region of visual cortex respond to stimuli within a restricted region of the visual field. Previous studies have characterized the population response of such neurons using a model that sums contrast linearly across the visual field. In this study we test linear spatial summation of population responses using blood oxygenation level dependent (BOLD) fMRI. We measure BOLD responses to a systematic set of contrast patterns and discover systematic deviation from linearity: the data are more accurately explained by a model in which a compressive static nonlinearity is applied after linear spatial summation. We find that the nonlinearity is present in early visual areas (e.g., V1, V2) and grows more pronounced in relatively anterior extrastriate areas (e.g., LO-2, VO-2). We then analyze the effect of compressive spatial summation in terms of changes in the position and size of a viewed object. Compressive spatial summation is consistent with tolerance to changes in position and size, an important characteristic of object representation.

    View details for DOI 10.1152/jn.00105.2013

    View details for Web of Science ID 000321843800019

    View details for PubMedID 23615546

  • Anatomy of the visual word form area: Adjacent cortical circuits and long-range white matter connections. Brain and language Yeatman, J. D., Rauschecker, A. M., Wandell, B. A. 2013; 125 (2): 146-155

    Abstract

    Circuitry in ventral occipital-temporal cortex is essential for seeing words. We analyze the circuitry within a specific ventral-occipital region, the visual word form area (VWFA). The VWFA is immediately adjacent to the retinotopically organized VO-1 and VO-2 visual field maps and lies medial and inferior to visual field maps within motion selective human cortex. Three distinct white matter fascicles pass within close proximity to the VWFA: (1) the inferior longitudinal fasciculus, (2) the inferior frontal occipital fasciculus, and (3) the vertical occipital fasciculus. The vertical occipital fasciculus terminates in or adjacent to the functionally defined VWFA voxels in every individual. The vertical occipital fasciculus projects dorsally to language and reading related cortex. The combination of functional responses from cortex and anatomical measures in the white matter provides an overview of how the written word is encoded and communicated along the ventral occipital-temporal circuitry for seeing words.

    View details for DOI 10.1016/j.bandl.2012.04.010

    View details for PubMedID 22632810

  • A Two-Stage Cascade Model of BOLD Responses in Human Visual Cortex. PLoS computational biology Kay, K. N., Winawer, J., Rokem, A., Mezer, A., Wandell, B. A. 2013; 9 (5)

    Abstract

    Visual neuroscientists have discovered fundamental properties of neural representation through careful analysis of responses to controlled stimuli. Typically, different properties are studied and modeled separately. To integrate our knowledge, it is necessary to build general models that begin with an input image and predict responses to a wide range of stimuli. In this study, we develop a model that accepts an arbitrary band-pass grayscale image as input and predicts blood oxygenation level dependent (BOLD) responses in early visual cortex as output. The model has a cascade architecture, consisting of two stages of linear and nonlinear operations. The first stage involves well-established computations-local oriented filters and divisive normalization-whereas the second stage involves novel computations-compressive spatial summation (a form of normalization) and a variance-like nonlinearity that generates selectivity for second-order contrast. The parameters of the model, which are estimated from BOLD data, vary systematically across visual field maps: compared to primary visual cortex, extrastriate maps generally have larger receptive field size, stronger levels of normalization, and increased selectivity for second-order contrast. Our results provide insight into how stimuli are encoded and transformed in successive stages of visual processing.

    View details for DOI 10.1371/journal.pcbi.1003079

    View details for PubMedID 23737741

  • GLMdenoise: a fast, automated technique for denoising task-based fMRI data. Frontiers in neuroscience Kay, K. N., Rokem, A., Winawer, J., Dougherty, R. F., Wandell, B. A. 2013; 7: 247-?

    Abstract

    In task-based functional magnetic resonance imaging (fMRI), researchers seek to measure fMRI signals related to a given task or condition. In many circumstances, measuring this signal of interest is limited by noise. In this study, we present GLMdenoise, a technique that improves signal-to-noise ratio (SNR) by entering noise regressors into a general linear model (GLM) analysis of fMRI data. The noise regressors are derived by conducting an initial model fit to determine voxels unrelated to the experimental paradigm, performing principal components analysis (PCA) on the time-series of these voxels, and using cross-validation to select the optimal number of principal components to use as noise regressors. Due to the use of data resampling, GLMdenoise requires and is best suited for datasets involving multiple runs (where conditions repeat across runs). We show that GLMdenoise consistently improves cross-validation accuracy of GLM estimates on a variety of event-related experimental datasets and is accompanied by substantial gains in SNR. To promote practical application of methods, we provide MATLAB code implementing GLMdenoise. Furthermore, to help compare GLMdenoise to other denoising methods, we present the Denoise Benchmark (DNB), a public database and architecture for evaluating denoising methods. The DNB consists of the datasets described in this paper, a code framework that enables automatic evaluation of a denoising method, and implementations of several denoising methods, including GLMdenoise, the use of motion parameters as noise regressors, ICA-based denoising, and RETROICOR/RVHRCOR. Using the DNB, we find that GLMdenoise performs best out of all of the denoising methods we tested.

    View details for DOI 10.3389/fnins.2013.00247

    View details for PubMedID 24381539

  • Tract Profiles of White Matter Properties: Automating Fiber-Tract Quantification PLOS ONE Yeatman, J. D., Dougherty, R. F., Myall, N. J., Wandell, B. A., Feldman, H. M. 2012; 7 (11)

    Abstract

    Tractography based on diffusion weighted imaging (DWI) data is a method for identifying the major white matter fascicles (tracts) in the living human brain. The health of these tracts is an important factor underlying many cognitive and neurological disorders. In vivo, tissue properties may vary systematically along each tract for several reasons: different populations of axons enter and exit the tract, and disease can strike at local positions within the tract. Hence quantifying and understanding diffusion measures along each fiber tract (Tract Profile) may reveal new insights into white matter development, function, and disease that are not obvious from mean measures of that tract. We demonstrate several novel findings related to Tract Profiles in the brains of typically developing children and children at risk for white matter injury secondary to preterm birth. First, fractional anisotropy (FA) values vary substantially within a tract but the Tract FA Profile is consistent across subjects. Thus, Tract Profiles contain far more information than mean diffusion measures. Second, developmental changes in FA occur at specific positions within the Tract Profile, rather than along the entire tract. Third, Tract Profiles can be used to compare white matter properties of individual patients to standardized Tract Profiles of a healthy population to elucidate unique features of that patient's clinical condition. Fourth, Tract Profiles can be used to evaluate the association between white matter properties and behavioral outcomes. Specifically, in the preterm group reading ability is positively correlated with FA measured at specific locations on the left arcuate and left superior longitudinal fasciculus and the magnitude of the correlation varies significantly along the Tract Profiles. We introduce open source software for automated fiber-tract quantification (AFQ) that measures Tract Profiles of MRI parameters for 18 white matter tracts. With further validation, AFQ Tract Profiles have potential for informing clinical management and decision-making.

    View details for DOI 10.1371/journal.pone.0049790

    View details for Web of Science ID 000311151900195

    View details for PubMedID 23166771

  • Plasticity and Stability of the Visual System in Human Achiasma NEURON Hoffmann, M. B., Kaule, F. R., Levin, N., Masuda, Y., Kumar, A., Gottlob, I., Horiguchi, H., Dougherty, R. F., Stadler, J., Wolynski, B., Speck, O., Kanowski, M., Liao, Y. J., Wandell, B. A., Dumoulin, S. O. 2012; 75 (3): 393-401

    Abstract

    The absence of the optic chiasm is an extraordinary and extreme abnormality in the nervous system. The abnormality produces highly atypical functional responses in the cortex, including overlapping hemifield representations and bilateral population receptive fields in both striate and extrastriate visual cortex. Even in the presence of these large functional abnormalities, the effect on visual perception and daily life is not easily detected. Here, we demonstrate that in two achiasmic humans the gross topography of the geniculostriate and occipital callosal connections remains largely unaltered. We conclude that visual function is preserved by reorganization of intracortical connections instead of large-scale reorganizations of the visual cortex. Thus, developmental mechanisms of local wiring within cortical maps compensate for the improper gross wiring to preserve function in human achiasma.

    View details for DOI 10.1016/j.neuron.2012.05.026

    View details for Web of Science ID 000307417700007

    View details for PubMedID 22884323

  • Position sensitivity in the visual word form area PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Rauschecker, A. M., Bowen, R. F., Parvizi, J., Wandell, B. A. 2012; 109 (24): E1568-E1577

    Abstract

    Seeing words involves the activity of neural circuitry within a small region in human ventral temporal cortex known as the visual word form area (VWFA). It is widely asserted that VWFA responses, which are essential for skilled reading, do not depend on the visual field position of the writing (position invariant). Such position invariance supports the hypothesis that the VWFA analyzes word forms at an abstract level, far removed from specific stimulus features. Using functional MRI pattern-classification techniques, we show that position information is encoded in the spatial pattern of VWFA responses. A right-hemisphere homolog (rVWFA) shows similarly position-sensitive responses. Furthermore, electrophysiological recordings in the human brain show position-sensitive VWFA response latencies. These findings show that position-sensitive information is present in the neural circuitry that conveys visual word form information to language areas. The presence of position sensitivity in the VWFA has implications for how word forms might be learned and stored within the reading circuitry.

    View details for DOI 10.1073/pnas.1121304109

    View details for Web of Science ID 000305511300011

    View details for PubMedID 22570498

  • Squaring cortex with color NATURE NEUROSCIENCE Wandell, B. A., Chichilnisky, E. J. 2012; 15 (6): 809-810

    View details for Web of Science ID 000304546700004

    View details for PubMedID 22627792

  • Digital camera simulation APPLIED OPTICS Farrell, J. E., Catrysse, P. B., Wandell, B. A. 2012; 51 (4): A80-A90

    Abstract

    We describe a simulation of the complete image processing pipeline of a digital camera, beginning with a radiometric description of the scene captured by the camera and ending with a radiometric description of the image rendered on a display. We show that there is a good correspondence between measured and simulated sensor performance. Through the use of simulation, we can quantify the effects of individual digital camera components on system performance and image quality. This computational approach can be helpful for both camera design and image quality assessment.

    View details for Web of Science ID 000300408400010

    View details for PubMedID 22307132

  • Connective field modeling. NeuroImage Haak, K. V., Winawer, J., Harvey, B. M., Renken, R., Dumoulin, S. O., Wandell, B. A., Cornelissen, F. W. 2012; 66C: 376-384

    Abstract

    The traditional way to study the properties of visual neurons is to measure their responses to visually presented stimuli. A second way to understand visual neurons is to characterize their responses in terms of activity elsewhere in the brain. Understanding the relationships between responses in distinct locations in the visual system is essential to clarify this network of cortical signaling pathways. Here, we describe and validate connective field modeling, a model-based analysis for estimating the dependence between signals in distinct cortical regions using functional magnetic resonance imaging (fMRI). Just as the receptive field of a visual neuron predicts its response as a function of stimulus position, the connective field of a neuron predicts its response as a function of activity in another part of the brain. Connective field modeling opens up a wide range of research opportunities to study information processing in the visual system and other topographically organized cortices.

    View details for PubMedID 23110879

  • Anatomical Properties of the Arcuate Fasciculus Predict Phonological and Reading Skills in Children JOURNAL OF COGNITIVE NEUROSCIENCE Yeatman, J. D., Dougherty, R. F., Rykhlevskaia, E., Sherbondy, A. J., Deutsch, G. K., Wandell, B. A., Ben-Shachar, M. 2011; 23 (11): 3304-3317

    Abstract

    For more than a century, neurologists have hypothesized that the arcuate fasciculus carries signals that are essential for language function; however, the relevance of the pathway for particular behaviors is highly controversial. The primary objective of this study was to use diffusion tensor imaging to examine the relationship between individual variation in the microstructural properties of arcuate fibers and behavioral measures of language and reading skills. A second objective was to use novel fiber-tracking methods to reassess estimates of arcuate lateralization. In a sample of 55 children, we found that measurements of diffusivity in the left arcuate correlate with phonological awareness skills and arcuate volume lateralization correlates with phonological memory and reading skills. Contrary to previous investigations that report the absence of the right arcuate in some subjects, we demonstrate that new techniques can identify the pathway in every individual. Our results provide empirical support for the role of the arcuate fasciculus in the development of reading skills.

    View details for Web of Science ID 000295869500011

    View details for PubMedID 21568636

  • Visual Feature-Tolerance in the Reading Network NEURON Rauschecker, A. M., Bowen, R. F., Perry, L. M., Kevan, A. M., Dougherty, R. F., Wandell, B. A. 2011; 71 (5): 941-953

    Abstract

    A century of neurology and neuroscience shows that seeing words depends on ventral occipital-temporal (VOT) circuitry. Typically, reading is learned using high-contrast line-contour words. We explored whether a specific VOT region, the visual word form area (VWFA), learns to see only these words or recognizes words independent of the specific shape-defining visual features. Word forms were created using atypical features (motion-dots, luminance-dots) whose statistical properties control word-visibility. We measured fMRI responses as word form visibility varied, and we used TMS to interfere with neural processing in specific cortical circuits, while subjects performed a lexical decision task. For all features, VWFA responses increased with word-visibility and correlated with performance. TMS applied to motion-specialized area hMT+ disrupted reading performance for motion-dots, but not line-contours or luminance-dots. A quantitative model describes feature-convergence in the VWFA and relates VWFA responses to behavioral performance. These findings suggest how visual feature-tolerance in the reading network arises through signal convergence from feature-specialized cortical areas.

    View details for DOI 10.1016/j.neuron.2011.06.036

    View details for Web of Science ID 000294877900017

    View details for PubMedID 21903085

  • The Development of Cortical Sensitivity to Visual Word Forms JOURNAL OF COGNITIVE NEUROSCIENCE Ben-Shachar, M., Dougherty, R. F., Deutsch, G. K., Wandell, B. A. 2011; 23 (9): 2387-2399

    Abstract

    The ability to extract visual word forms quickly and efficiently is essential for using reading as a tool for learning. We describe the first longitudinal fMRI study to chart individual changes in cortical sensitivity to written words as reading develops. We conducted four annual measurements of brain function and reading skills in a heterogeneous group of children, initially 7-12 years old. The results show age-related increase in children's cortical sensitivity to word visibility in posterior left occipito-temporal sulcus (LOTS), nearby the anatomical location of the visual word form area. Moreover, the rate of increase in LOTS word sensitivity specifically correlates with the rate of improvement in sight word efficiency, a measure of speeded overt word reading. Other cortical regions, including V1, posterior parietal cortex, and the right homologue of LOTS, did not demonstrate such developmental changes. These results provide developmental support for the hypothesis that LOTS is part of the cortical circuitry that extracts visual word forms quickly and efficiently and highlight the importance of developing cortical sensitivity to word visibility in reading acquisition.

    View details for Web of Science ID 000292508900024

    View details for PubMedID 21261451

  • Imaging retinotopic maps in the human brain VISION RESEARCH Wandell, B. A., Winawer, J. 2011; 51 (7): 718-737

    Abstract

    A quarter-century ago visual neuroscientists had little information about the number and organization of retinotopic maps in human visual cortex. The advent of functional magnetic resonance imaging (MRI), a non-invasive, spatially-resolved technique for measuring brain activity, provided a wealth of data about human retinotopic maps. Just as there are differences amongst non-human primate maps, the human maps have their own unique properties. Many human maps can be measured reliably in individual subjects during experimental sessions lasting less than an hour. The efficiency of the measurements and the relatively large amplitude of functional MRI signals in visual cortex make it possible to develop quantitative models of functional responses within specific maps in individual subjects. During this last quarter-century, there has also been significant progress in measuring properties of the human brain at a range of length and time scales, including white matter pathways, macroscopic properties of gray and white matter, and cellular and molecular tissue properties. We hope the next 25years will see a great deal of work that aims to integrate these data by modeling the network of visual signals. We do not know what such theories will look like, but the characterization of human retinotopic maps from the last 25years is likely to be an important part of future ideas about visual computations.

    View details for DOI 10.1016/j.visres.2010.08.004

    View details for Web of Science ID 000290061300008

    View details for PubMedID 20692278

  • The neurobiological basis of seeing words. Annals of the New York Academy of Sciences Wandell, B. A. 2011; 1224: 63-80

    Abstract

    This review summarizes recent ideas about the cortical circuits for seeing words, an important part of the brain system for reading. Historically, the link between the visual cortex and reading has been contentious. One influential position is that the visual cortex plays a minimal role, limited to identifying contours, and that information about these contours is delivered to cortical regions specialized for reading and language. An alternative position is that specializations for seeing words develop within the visual cortex itself. Modern neuroimaging measurements-including both functional magnetic resonance imaging (fMRI) and diffusion weighted imaging with tractography (DTI) data-support the position that circuitry for seeing the statistical regularities of word forms develops within the ventral occipitotemporal cortex, which also contains important circuitry for seeing faces, colors, and forms. This review explains new findings about the visual pathways, including visual field maps, as well as new findings about how we see words. The measurements from the two fields are in close cortical proximity, and there are good opportunities for coordinating theoretical ideas about function in the ventral occipitotemporal cortex.

    View details for DOI 10.1111/j.1749-6632.2010.05954.x

    View details for PubMedID 21486296

  • Bound pool fractions complement diffusion measures to describe white matter micro and macrostructure NEUROIMAGE Stikov, N., Perry, L. M., Mezer, A., Rykhlevskaia, E., Wandell, B. A., Pauly, J. M., Dougherty, R. F. 2011; 54 (2): 1112-1121

    Abstract

    Diffusion imaging and bound pool fraction (BPF) mapping are two quantitative magnetic resonance imaging techniques that measure microstructural features of the white matter of the brain. Diffusion imaging provides a quantitative measure of the diffusivity of water in tissue. BPF mapping is a quantitative magnetization transfer (qMT) technique that estimates the proportion of exchanging protons bound to macromolecules, such as those found in myelin, and is thus a more direct measure of myelin content than diffusion. In this work, we combined BPF estimates of macromolecular content with measurements of diffusivity within human white matter tracts. Within the white matter, the correlation between BPFs and diffusivity measures such as fractional anisotropy and radial diffusivity was modest, suggesting that diffusion tensor imaging and bound pool fractions are complementary techniques. We found that several major tracts have high BPF, suggesting a higher density of myelin in these tracts. We interpret these results in the context of a quantitative tissue model.

    View details for DOI 10.1016/j.neuroimage.2010.08.068

    View details for Web of Science ID 000285486000036

    View details for PubMedID 20828622

  • Task-Dependent V1 Responses in Human Retinitis Pigmentosa INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Masuda, Y., Horiguchi, H., Dumoulin, S. O., Furuta, A., Miyauchi, S., Nakadomari, S., Wandell, B. A. 2010; 51 (10): 5356-5364

    Abstract

    During measurement with functional MRI (fMRI) during passive viewing, subjects with macular degeneration (MD) have a large unresponsive lesion projection zone (LPZ) in V1. fMRI responses can be evoked from the LPZ when subjects engage in a stimulus-related task. The authors report fMRI measurements on a different class of subjects, those with retinitis pigmentosa (RP), who have intact foveal vision but peripheral visual field loss.The authors measured three RP subjects and two control subjects. fMRI was performed while the subjects viewed drifting contrast pattern stimuli. The subjects passively viewed the stimuli or performed a stimulus-related task.During passive viewing, the BOLD response in the posterior calcarine cortex of all RP subjects was in phase with the stimulus. A bordering, anterior LPZ could be identified by responses that were in opposite phase to the stimulus. When the RP subjects made stimulus-related judgments, however, the LPZ responses changed: the responses modulated in phase with the stimulus and task. In control subjects, the responses in a simulated V1 LPZ were unchanged between the passive and the stimulus-related judgment conditions.Task-dependent LPZ responses are present in RP subjects, similar to responses measured in MD subjects. The results are consistent with the hypothesis that deleting the retinal input to the LPZ unmasks preexisting extrastriate feedback signals that are present across V1. The authors discuss the implications of this hypothesis for visual therapy designed to replace the missing V1 LPZ inputs and to restore vision.

    View details for DOI 10.1167/iovs.09-4775

    View details for Web of Science ID 000282275500065

    View details for PubMedID 20445118

  • Congenital Achiasma and See-Saw Nystagmus in VACTERL Syndrome JOURNAL OF NEURO-OPHTHALMOLOGY Prakash, S., Dumoulin, S. O., Fischbein, N., Wandell, B. A., Liao, Y. J. 2010; 30 (1): 45-48

    Abstract

    A 29-year-old man with vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal defects, and limb defects (VACTERL) presented with headache, photophobia, and worsening nystagmus. He had near-normal visual acuity and visual fields, absent stereopsis, and see-saw nystagmus. Brain MRI revealed a thin remnant of the optic chiasm but normal-sized optic nerves. Functional MRI during monocular visual stimulation demonstrated non-crossing of the visual evoked responses in the occipital cortex, confirming achiasma. These findings have not previously been reported in VACTERL.

    View details for DOI 10.1097/WNO.0b013e3181c28fc0

    View details for Web of Science ID 000275061500012

    View details for PubMedID 20182207

  • Cortical Maps and White Matter Tracts following Long Period of Visual Deprivation and Retinal Image Restoration NEURON Levin, N., Dumoulin, S. O., Winawer, J., Dougherty, R. F., Wandell, B. A. 2010; 65 (1): 21-31

    Abstract

    Abnormal visual input during development has dramatic effects on the visual system. How does the adult visual system respond when input is corrected? MM lost his left eye and became blind in the right due to corneal damage at the age of 3. At age 46, MM regained his retinal image, but his visual abilities, even seven years following the surgery, remain severely limited, and he does not rely on vision for daily life. Neuroimaging measurements reveal several differences among MM, sighted controls, sighted monocular, and early blind subjects. We speculate that these differences stem from damage during the critical period in development of retinal neurons with small, foveal receptive fields. In this case, restoration of functional vision requires more than improving retinal image contrast. In general, visual restoration will require accounting for the developmental trajectory of the individual and the consequences of the early deprivation on cortical circuitry.

    View details for DOI 10.1016/j.neuron.2009.12.006

    View details for Web of Science ID 000273791200005

    View details for PubMedID 20152110

  • Frontoparietal white matter diffusion properties predict mental arithmetic skills in children PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Tsang, J. M., Dougherty, R. F., Deutsch, G. K., Wandell, B. A., Ben-Shachar, M. 2009; 106 (52): 22546-22551

    Abstract

    Functional MRI studies of mental arithmetic consistently report blood oxygen level-dependent signals in the parietal and frontal regions. We tested whether white matter pathways connecting these regions are related to mental arithmetic ability by using diffusion tensor imaging (DTI) to measure these pathways in 28 children (age 10-15 years, 14 girls) and assessing their mental arithmetic skills. For each child, we identified anatomically the anterior portion of the superior longitudinal fasciculus (aSLF), a pathway connecting parietal and frontal cortex. We measured fractional anisotropy in a core region centered along the length of the aSLF. Fractional anisotropy in the left aSLF positively correlates with arithmetic approximation skill, as measured by a mental addition task with approximate answer choices. The correlation is stable in adjacent core aSLF regions but lower toward the pathway endpoints. The correlation is not explained by shared variance with other cognitive abilities and did not pass significance in the right aSLF. These measurements used DTI, a structural method, to test a specific functional model of mental arithmetic.

    View details for DOI 10.1073/pnas.0906094106

    View details for Web of Science ID 000273178700090

    View details for PubMedID 19948963

  • Visual Field Maps, Population Receptive Field Sizes, and Visual Field Coverage in the Human MT plus Complex JOURNAL OF NEUROPHYSIOLOGY Amano, K., Wandell, B. A., Dumoulin, S. O. 2009; 102 (5): 2704-2718

    Abstract

    Human neuroimaging experiments typically localize motion-selective cortex (MT+) by contrasting responses to stationary and moving stimuli. It has long been suspected that MT+, located on the lateral surface at the temporal-occipital (TO) boundary, contains several distinct visual field maps, although only one coarse map has been measured. Using a novel functional MRI model-based method we identified two maps-TO-1 and TO-2-and measured population receptive field (pRF) sizes within these maps. The angular representation of the first map, TO-1, has a lower vertical meridian on its posterior side at the boundary with the lateral-occipital cortex (i.e., the LO-2 portion). The angular representation continues through horizontal to the upper vertical meridian at the boundary with the second map, TO-2. The TO-2 angle map reverses from upper to lower visual field at increasingly anterior positions. The TO maps share a parallel eccentricity map in which center-to-periphery is represented in the ventral-to-dorsal direction; both maps have an expanded foveal representation. There is a progressive increase in the pRF size from V1/2/3 to LO-1/2 and TO-1/2, with the largest pRF sizes in TO-2. Further, within each map the pRF size increases as a function of eccentricity. The visual field coverage of both maps extends into the ipsilateral visual field, with larger sensitivity to peripheral ipsilateral stimuli in TO-2 than that in TO-1. The TO maps provide a functional segmentation of human motion-sensitive cortex that enables a more complete characterization of processing in human motion-selective cortex.

    View details for DOI 10.1152/jn.00102.2009

    View details for Web of Science ID 000271467300012

    View details for PubMedID 19587323

  • Two temporal channels in human V1 identified using fMRI NEUROIMAGE Horiguchi, H., Nakadomari, S., Misaki, M., Wandell, B. A. 2009; 47 (1): 273-280

    Abstract

    Human visual sensitivity to a fairly broad class of dynamic stimuli can be modeled accurately using two temporal channels. Here, we analyze fMRI measurements of the temporal step response to spatially uniform stimuli to estimate these channels in human primary visual cortex (V1). In agreement with the psychophysical literature, the V1 fMRI temporal responses are modeled accurately as a mixture of two (transient and sustained) channels. We derive estimates of the relative contributions from these two channels at a range of eccentricities. We find that all portions of V1 contain a significant transient response. The central visual field representation includes a significant sustained response, but the amplitude of the sustained channel signal declines with eccentricity. The sustained signals may reflect the emphasis on pattern recognition and color in the central visual field; the dominant transient response in the visual periphery may reflect responses in the human visual attention system.

    View details for DOI 10.1016/j.neuroimage.2009.03.078

    View details for Web of Science ID 000266975300030

    View details for PubMedID 19361561

  • Think global, act local; projectome estimation with BlueMatter. Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention Sherbondy, A. J., Dougherty, R. F., Ananthanarayanan, R., Modha, D. S., Wandell, B. A. 2009; 12: 861-868

    Abstract

    Estimating the complete set of white matter fascicles (the projectome) from diffusion data requires evaluating an enormous number of potential pathways; consequently, most algorithms use computationally efficient greedy methods to search for pathways. The limitation of this approach is that critical global parameters--such as data prediction error and white matter volume conservation--are not taken into account. We describe BlueMatter, a parallel algorithm for global projectome evaluation, which uniquely accounts for global prediction error and volume conservation. Leveraging the BlueGene/L supercomputing architecture, BlueMatter explores a massive database of 180 billion candidate fascicles. The candidates are derived from several sources, including atlases and multiple tractography algorithms. Using BlueMatter we created the highest resolution, volume-conserved projectome of the human brain.

    View details for PubMedID 20426069

  • V1 Projection Zone Signals in Human Macular Degeneration Depend on Task, not Stimulus CEREBRAL CORTEX Masuda, Y., Dumoulin, S. O., Nakadomari, S., Wandell, B. A. 2008; 18 (11): 2483-2493

    Abstract

    We used functional magnetic resonance imaging to assess abnormal cortical signals in humans with juvenile macular degeneration (JMD). These signals have been interpreted as indicating large-scale cortical reorganization. Subjects viewed a stimulus passively or performed a task; the task was either related or unrelated to the stimulus. During passive viewing, or while performing tasks unrelated to the stimulus, there were large unresponsive V1 regions. These regions included the foveal projection zone, and we refer to them as the lesion projection zone (LPZ). In 3 JMD subjects, we observed highly significant responses in the LPZ while they performed stimulus-related judgments. In control subjects, where we presented the stimulus only within the peripheral visual field, there was no V1 response in the foveal projection zone in any condition. The difference between JMD and control responses can be explained by hypotheses that have very different implications for V1 reorganization. In controls retinal afferents carry signals indicating the presence of a uniform (zero-contrast) region of the visual field. Deletion of retinal input may 1) spur the formation of new cortical pathways that carry task-dependent signals (reorganization), or 2) unmask preexisting task-dependent cortical signals that ordinarily are suppressed by the deleted signals (no reorganization).

    View details for DOI 10.1093/cercor/bhm256

    View details for Web of Science ID 000260135700002

    View details for PubMedID 18250083

  • Full-brain coverage and high-resolution Imaging capabilities of passband b-SSFP fMRI at 3T MAGNETIC RESONANCE IN MEDICINE Lee, J. H., Dumoulin, S. O., Saritas, E. U., Glover, G. H., Wandell, B. A., Nishimura, D. G., Pauly, J. M. 2008; 59 (5): 1099-1110

    Abstract

    Passband balanced-steady-state free precession (b-SSFP) fMRI is a recently developed method that utilizes the passband (flat portion) of the b-SSFP off-resonance response to measure MR signal changes elicited by changes in tissue oxygenation following increases in neuronal activity. Rapid refocusing and short readout durations of b-SSFP, combined with the relatively large flat portion of the b-SSFP off-resonance spectrum allows distortion-free full-brain coverage with only two acquisitions. This allows for high-resolution functional imaging, without the spatial distortion frequently encountered in conventional high-resolution functional images. Finally, the 3D imaging compatibility of the b-SSFP acquisitions permits isotropic-voxel-size high-resolution acquisitions. In this study we address some of the major technical issues involved in obtaining passband b-SSFP-based functional brain images with practical imaging parameters and demonstrate the advantages through breath-holding and visual field mapping experiments.

    View details for DOI 10.1002/mrm.21576

    View details for Web of Science ID 000255230700020

    View details for PubMedID 18421687

  • What's in your mind? NATURE NEUROSCIENCE Wandell, B. A. 2008; 11 (4): 384-385

    View details for DOI 10.1038/nn0408-384

    View details for Web of Science ID 000254359300005

    View details for PubMedID 18368043

  • Population receptive field estimates in human visual cortex NEUROIMAGE Dumoulin, S. O., Wandell, B. A. 2008; 39 (2): 647-660

    Abstract

    We introduce functional MRI methods for estimating the neuronal population receptive field (pRF). These methods build on conventional visual field mapping that measures responses to ring and wedge patterns shown at a series of visual field locations and estimates the single position in the visual field that produces the largest response. The new method computes a model of the population receptive field from responses to a wide range of stimuli and estimates the visual field map as well as other neuronal population properties, such as receptive field size and laterality. The visual field maps obtained with the pRF method are more accurate than those obtained using conventional visual field mapping, and we trace with high precision the visual field maps to the center of the foveal representation. We report quantitative estimates of pRF size in medial, lateral and ventral occipital regions of human visual cortex. Also, we quantify the amount of input from ipsi- and contralateral visual fields. The human pRF size estimates in V1-V3 agree well with electrophysiological receptive field measurements at a range of eccentricities in corresponding locations within monkey and human visual field maps. The pRF method is non-invasive and can be applied to a wide range of conditions when it is useful to link fMRI signals in the visual pathways to neuronal receptive fields.

    View details for DOI 10.1016/j.neuroimage.2007.09.034

    View details for Web of Science ID 000251634400011

    View details for PubMedID 17977024

  • fMRI measurements of color in macaque and human JOURNAL OF VISION Wade, A., Augath, M., Logothetis, N., Wandell, B. 2008; 8 (10)

    Abstract

    We have used fMRI to measure responses to chromatic and achromatic contrast in retinotopically defined regions of macaque and human visual cortex. We make four observations. Firstly, the relative amplitudes of responses to color and luminance stimuli in macaque area V1 are similar to those previously observed in human fMRI experiments. Secondly, the dorsal and ventral subdivisions of macaque area V4 respond in a similar way to opponent (L--M)-cone chromatic contrast suggesting that they are part of a single functional area. Thirdly, we find that macaque area V4, like area V1, responds preferentially to chromatic contrast compared to luminance contrast and the degree of preference is strongly influenced by the temporal frequency of the stimulus. Finally, we observe that while macaque V4d is a region on the dorsal surface of the macaque visual cortex that responds robustly to chromatic stimuli, human chromatic responses to identical stimuli are largely confined to the ventral surface suggesting a fundamental difference in the topographical organization of higher visual areas between humans and macaques.

    View details for DOI 10.1167/8.10.6

    View details for Web of Science ID 000262231200007

    View details for PubMedID 19146348

  • Identifying the human optic radiation using diffusion imaging and fiber tractography JOURNAL OF VISION Sherbondy, A. J., Dougherty, R. F., Napel, S., Wandell, B. A. 2008; 8 (10)

    Abstract

    Measuring the properties of the white matter pathways from retina to cortex in the living human brain will have many uses for understanding visual performance and guiding clinical treatment. For example, identifying the Meyer's loop portion of the optic radiation (OR) has clinical significance because of the large number of temporal lobe resections. We use diffusion tensor imaging and fiber tractography (DTI-FT) to identify the most likely pathway between the lateral geniculate nucleus (LGN) and the calcarine sulcus in sixteen hemispheres of eight healthy volunteers. Quantitative population comparisons between DTI-FT estimates and published postmortem dissections match with a spatial precision of about 1 mm. The OR can be divided into three bundles that are segmented based on the direction of the fibers as they leave the LGN: Meyer's loop, central, and direct. The longitudinal and radial diffusivities of the three bundles do not differ within the measurement noise; there is a small difference in the radial diffusivity between the right and left hemispheres. We find that the anterior tip of Meyer's loop is 28 +/- 3 mm posterior to the temporal pole, and the population range is 1 cm. Hence, it is important to identify the location of this bundle in individual subjects or patients.

    View details for DOI 10.1167/8.10.12

    View details for Web of Science ID 000262231200013

    View details for PubMedID 19146354

  • ConTrack: Finding the most likely pathways between brain regions using diffusion tractography JOURNAL OF VISION Sherbondy, A. J., Dougherty, R. F., Ben-Shachar, M., Napel, S., Wandell, B. A. 2008; 8 (9)

    Abstract

    Magnetic resonance diffusion-weighted imaging coupled with fiber tractography (DFT) is the only non-invasive method for measuring white matter pathways in the living human brain. DFT is often used to discover new pathways. But there are also many applications, particularly in visual neuroscience, in which we are confident that two brain regions are connected, and we wish to find the most likely pathway forming the connection. In several cases, current DFT algorithms fail to find these candidate pathways. To overcome this limitation, we have developed a probabilistic DFT algorithm (ConTrack) that identifies the most likely pathways between two regions. We introduce the algorithm in three parts: a sampler to generate a large set of potential pathways, a scoring algorithm that measures the likelihood of a pathway, and an inferential step to identify the most likely pathways connecting two regions. In a series of experiments using human data, we show that ConTrack estimates known pathways at positions that are consistent with those found using a high quality deterministic algorithm. Further we show that separating sampling and scoring enables ConTrack to identify valid pathways, known to exist, that are missed by other deterministic and probabilistic DFT algorithms.

    View details for DOI 10.1167/8.9.15

    View details for Web of Science ID 000258709300015

    View details for PubMedID 18831651

  • Contrast responsivity in MT plus correlates with phonological awareness and reading measures in children NEUROIMAGE Ben-Shachar, M., Dougherty, R. F., Deutsch, G. K., Wandell, B. A. 2007; 37 (4): 1396-1406

    Abstract

    There are several independent sets of findings concerning the neural basis of reading. One set demonstrates a powerful relationship between phonological processing and reading skills. Another set reveals a relationship between visual responses in the motion pathways and reading skills. It is widely assumed that these two findings are unrelated. We tested the hypothesis that phonological awareness is related to motion responsivity in children's MT+. We measured BOLD signals to drifting gratings as a function of contrast. Subjects were 35 children ages 7-12 years with a wide range of reading skills. Contrast responsivity in MT+, but not V1, was correlated with phonological awareness and to a lesser extent with two other measures of reading. No correlation was found between MT+ signals and rapid naming, age or general IQ measures. These results establish an important link between visual and phonological processing in children and suggest that MT+ responsivity is a marker for healthy reading development.

    View details for DOI 10.1016/j.neuroimage.2007.05.060

    View details for Web of Science ID 000249773600043

    View details for PubMedID 17689981

  • Differential sensitivity to words and shapes in ventral occipito-temporal cortex CEREBRAL CORTEX Ben-Shachar, M., Dougherty, R. F., Deutsch, G. K., Wandell, B. A. 2007; 17 (7): 1604-1611

    Abstract

    Efficient extraction of shape information is essential for proficient reading but the role of cortical mechanisms of shape analysis in word reading is not well understood. We studied cortical responses to written words while parametrically varying the amount of visual noise applied to the word stimuli. In only a few regions along the ventral surface, cortical responses increased with word visibility. We found consistently increasing responses in bilateral posterior occipito-temporal sulcus (pOTS), at an anatomical location that closely matches the "visual word form area". In other cortical regions, such as V1, responses remained constant regardless of the noise level. We performed 3 additional tests to assess the functional specialization of pOTS responses for written word processing. We asked whether pOTS responses are 1) left lateralized, 2) more sensitive to words than to line drawings or false fonts, and 3) invariant for visual hemifield of words but not other stimuli. We found that left and right pOTS response functions both had highest sensitivity for words, intermediate for line drawings, and lowest for false fonts. Visual hemifield invariance was similar for words and line drawings. These results suggest that left and right pOTS are both involved in shape processing, with enhanced efficiency for processing visual word forms.

    View details for DOI 10.1093/cercor/bhl071

    View details for Web of Science ID 000247349000011

    View details for PubMedID 16956978

  • Temporal-callosal pathway diffusivity predicts phonological skills in children PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Dougherty, R. F., Ben-Shachar, M., Deutsch, G. K., Hernandez, A., Fox, G. R., Wandell, B. A. 2007; 104 (20): 8556-8561

    Abstract

    The development of skilled reading requires efficient communication between distributed brain regions. By using diffusion tensor imaging, we assessed the interhemispheric connections in a group of children with a wide range of reading abilities. We segmented the callosal fibers into regions based on their likely cortical projection zones, and we measured diffusion properties in these segmented regions. Phonological awareness (a key factor in reading acquisition) was positively correlated with diffusivity perpendicular to the main axis of the callosal fibers that connect the temporal lobes. These results could be explained by several physiological properties. For example, good readers may have fewer but larger axons connecting left and right temporal lobes, or their axon membranes in these regions may be more permeable than the membranes of poor readers. These measurements are consistent with previous work suggesting that good readers have reduced interhemispheric connectivity and are better at processing rapidly changing visual and auditory stimuli.

    View details for DOI 10.1073/pnas.0608961104

    View details for Web of Science ID 000246599900065

    View details for PubMedID 17483487

  • Assessment of stimulus-induced changes in human V1 visual field maps JOURNAL OF NEUROPHYSIOLOGY Liu, J. V., Ashida, H., Smith, A. T., Wandell, B. A. 2006; 96 (6): 3398-3408

    Abstract

    Visual cortex contains a set of field maps in which nearby scene points are represented in the responses of nearby neurons. We tested a recent hypothesis that the visual field map in primary visual cortex (V1) is dynamic, changing in response to stimulus motion direction. The original experimental report replicates, but further experimental and analytical investigations do not support, the interpretation of the results. The V1 map remains invariant when measured using stimuli moving in different directions. The measurements can be explained by small and systematic response amplitude differences that arise when probing with stimuli moving in different directions.

    View details for DOI 10.1152/jn.00556.2006

    View details for Web of Science ID 000242177800056

    View details for PubMedID 17005617

  • No functional magnetic resonance imaging evidence for brightness and color filling-in in early human visual cortex JOURNAL OF NEUROSCIENCE Cornelissen, F. W., Wade, A. R., Vladusich, T., Dougherty, R. F., Wandell, B. A. 2006; 26 (14): 3634-3641

    Abstract

    The brightness and color of a surface depends on its contrast with nearby surfaces. For example, a gray surface can appear very light when surrounded by a black surface or dark when surrounded by a white surface. Some theories suggest that perceived surface brightness and color is represented explicitly by neural signals in cortical visual field maps; these neural signals are not initiated by the stimulus itself but rather by the contrast signals at the borders. Here, we use functional magnetic resonance imaging (fMRI) to search for such neural "filling-in" signals. Although we find the usual strong relationship between local contrast and fMRI response, when perceived brightness or color changes are induced by modulating a surrounding field, rather than the surface itself, we find there is no corresponding local modulation in primary visual cortex or other nearby retinotopic maps. Moreover, when we model the obtained fMRI responses, we find strong evidence for contributions of both local and long-range edge responses. We argue that such extended edge responses may be caused by neurons previously identified in neurophysiological studies as being brightness responsive, a characterization that may therefore need to be revised. We conclude that the visual field maps of human V1 and V2 do not contain filled-in, topographical representations of surface brightness and color.

    View details for DOI 10.1523/JNEUROSCI.4382-05.2006

    View details for Web of Science ID 000236552400004

    View details for PubMedID 16597716

  • Visual field maps and stimulus selectivity in human ventral occipital cortex NATURE NEUROSCIENCE Brewer, A. A., Liu, J. J., Wade, A. R., Wandell, B. A. 2005; 8 (8): 1102-1109

    Abstract

    Human visual cortex is organized into distinct visual field maps whose locations and properties provide important information about visual computations. There are two conflicting models of the organization and computational role of ventral occipital visual field maps. We report new functional MRI measurements that test these models. We also present the first coordinated measurements of visual field maps and stimulus responsivity to color, objects and faces in ventral occipital cortex. These measurements support a model that includes a hemifield map, hV4, adjacent to the central field representation of ventral V3. In addition, the measurements demonstrate a cluster of visual field maps in ventral occipital cortex (VO cluster) anterior to hV4. We describe the organization and stimulus responsivity of two new hemifield maps, VO-1 and VO-2, within this cluster. The maps and stimulus responsivity support a general organization of visual cortex based on clusters of maps that serve distinct computational functions.

    View details for DOI 10.1038/nn1507

    View details for Web of Science ID 000230760200023

    View details for PubMedID 16025108

  • Lack of long-term cortical reorganization after macaque retinal lesions NATURE Smirnakis, S. M., Brewer, A. A., Schmid, M. C., Tolias, A. S., Schuz, A., Augath, M., Inhoffen, W., Wandell, B. A., Logothetis, N. K. 2005; 435 (7040): 300-307

    Abstract

    Several aspects of cortical organization are thought to remain plastic into adulthood, allowing cortical sensorimotor maps to be modified continuously by experience. This dynamic nature of cortical circuitry is important for learning, as well as for repair after injury to the nervous system. Electrophysiology studies suggest that adult macaque primary visual cortex (V1) undergoes large-scale reorganization within a few months after retinal lesioning, but this issue has not been conclusively settled. Here we applied the technique of functional magnetic resonance imaging (fMRI) to detect changes in the cortical topography of macaque area V1 after binocular retinal lesions. fMRI allows non-invasive, in vivo, long-term monitoring of cortical activity with a wide field of view, sampling signals from multiple neurons per unit cortical area. We show that, in contrast with previous studies, adult macaque V1 does not approach normal responsivity during 7.5 months of follow-up after retinal lesions, and its topography does not change. Electrophysiology experiments corroborated the fMRI results. This indicates that adult macaque V1 has limited potential for reorganization in the months following retinal injury.

    View details for DOI 10.1038/nature03495

    View details for Web of Science ID 000229185000036

    View details for PubMedID 15902248

  • Functional organization of human occipital-callosal fiber tracts PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Dougherty, R. F., Ben-Shachar, M., Bammer, R., Brewer, A. A., Wandell, B. A. 2005; 102 (20): 7350-7355

    Abstract

    Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia. To assess the reliability of the DTI-FT measurements, occipital-callosal projections were estimated from each subject's left and right hemispheres independently. The left and right estimates converged onto the same positions within the splenium. We further characterized the properties of the estimated occipital-callosal fiber tracts by combining them with functional MRI. We used functional MRI to identify visual field maps in cortex and labeled fibers by the cortical functional response at the fiber endpoint. This labeling reveals a regular organization of the fibers within the splenium. The dorsal visual maps (dorsal V3, V3A, V3B, V7) send projections through a large band in the middle of the splenium, whereas ventral visual maps (ventral V3, V4) send projections through the inferior-anterior corner of the splenium. The agreement between the independent left/right estimates, further supported by previous descriptions of homologous tracts in macaque, validates the DTI-FT methods. However, a principal limitation of these methods is low sensitivity: a large number of fiber tracts that connect homotopic regions of ventral and lateral visual cortex were undetected. We conclude that most of the estimated tracts are real and can be localized with a precision of 1-2 mm, but many tracts are missed because of data and algorithm limitations.

    View details for DOI 10.1073/pnas.0500003102

    View details for Web of Science ID 000229292200053

    View details for PubMedID 15883384

  • Visual field map clusters in human cortex PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Wandell, B. A., Brewer, A. A., Dougherty, R. F. 2005; 360 (1456): 693-707

    Abstract

    We describe the location and general properties of nine human visual field maps. The cortical location of each map, as well as many examples of the eccentricity and angular representations within these maps, are shown in a series of images that summarize a large set of functional MRI data. The organization and properties of these maps are compared and contrasted with descriptions by other investigators. We hypothesize that the human visual field maps are arranged in several clusters, each comprising a group of maps that share a common foveal representation and semicircular eccentricity map. The spatial organization of these clusters suggests that the perceptual processing within each cluster serves related functions.

    View details for DOI 10.1098/rstb.2005.1628

    View details for Web of Science ID 000229929100004

    View details for PubMedID 15937008

  • Specializations for chromatic and temporal signals in human visual cortex JOURNAL OF NEUROSCIENCE Liu, J. J., Wandell, B. A. 2005; 25 (13): 3459-3468

    Abstract

    Neurological case studies and qualitative measurements suggest that regions within human extrastriate cortex are specialized for different perceptual functions, including color. However, there are few quantitative measurements of human extrastriate color specializations. We studied the chromatic and temporal responses in several different clusters of human visual field maps using functional magnetic resonance imaging. Contrast response functions were measured for luminance [(L + M)-cone], red-green [(L - M)-cone] and blue-yellow (S-cone) modulations at various temporal frequencies. In primary visual cortex (V1), temporal responsivities to luminance and red-green modulations are approximately constant up to 10 Hz, but responsivities to blue-yellow modulations decrease significantly. In ventral occipital cortex (VO), all colors elicit strong responses, and, for each color, low temporal frequency modulations are more effective than high temporal frequency modulations. Hence, VO represents the full range of color information but does not respond well to rapid modulations. Conversely, in human motion-selective cortex (MT+) and V3A, blue-yellow modulations elicit very weak responses, whereas luminance and red-green high temporal frequency modulations are equally or more effective than low temporal frequency modulations. Hence, these dorsal occipital regions respond well to rapid modulations, but not all color information is represented. Similar to human motion perception, MT+ and V3A respond powerfully to all temporal frequencies but only to some colors. Similar to human color perception, VO responds powerfully to all colors but only to relatively low temporal frequencies.

    View details for DOI 10.1523/JNEUROSCI-4206-04.2005

    View details for Web of Science ID 000228038200023

    View details for PubMedID 15800201

  • Predominantly extra-retinotopic cortical response to pattern symmetry NEUROIMAGE Tyler, C. W., Baseler, H. A., Kontsevich, L. L., Likova, L. T., Wade, A. R., Wandell, B. A. 2005; 24 (2): 306-314

    Abstract

    Symmetry along one or more axes is a key property of objects and biological organisms. We report on a bilateral visual region of occipital cortex that responds strongly to the presence of multiple symmetries in the viewed image. The stimuli consisted of random dots organized in fourfold and onefold mirror-symmetric patterns, against random control stimuli. The contrast between symmetric and random patterns produced negligible or inconsistent activation of the primary visual projection area V1 or of other medial occipital projection areas. However, there was strong symmetry-specific activation in extra-retinotopic lateral occipital cortex. The high level of activation in this region of cortex may represent part of a general class of computations that require integration of information across a large span of the visual field.

    View details for DOI 10.1016/j.neuroimage.2004.09.018

    View details for Web of Science ID 000226454500004

    View details for PubMedID 15627573

  • Occipital-callosal pathways in children - Validation and atlas development WHITE MATTER IN COGNITIVE NEUROSCIENCE: ADVANCES IN DIFFUSION TENSOR IMAGING AND ITS APPLICATIONS Dougherty, R. F., Ben-Shachar, M., Deutsch, G., Potanina, P., Bammer, R., Wandell, B. A. 2005; 1064: 98-?

    Abstract

    Diffusion tensor imaging and fiber tracking were used to measure fiber bundles connecting the two occipital lobes in 53 children of 7-12 years of age. Independent fiber bundle estimates originating from the two hemispheres converge onto the lower half of the splenium. This observation validates the basic methodology and suggests that most occipital-callosal fibers connect the two occipital lobes. Within the splenium, fiber bundles are organized in a regular pattern with respect to their cortical projection zones. Visual cortex dorsal to calcarine projects through a large band that fills much of the inferior half of the splenium, while cortex ventral to calcarine sends projections through a band at the anterior inferior edge of the splenium. Pathways projecting to the occipital pole and lateral-occipital regions overlap the dorsal and ventral groups slightly anterior to the center of the splenium. To visualize these pathways in a typical brain, we combined the data into an atlas. The estimated occipital-callosal fiber paths from the atlas form the walls of the occipital horn of the lateral ventricle, with dorsal paths forming the medial wall and the ventral paths bifurcating into a medial tract to form the inferior-medial wall and a superior tract that joins the lateral-occipital paths to form the superior wall of the ventricle. The properties of these fiber bundles match those of the hypothetical pathways described in the neurological literature on alexia.

    View details for DOI 10.1196/annals.1340.017

    View details for Web of Science ID 000235430200008

    View details for PubMedID 16394151

  • Cone signal interactions in direction-selective neurons in the middle temporal visual area (MT) JOURNAL OF VISION Barberini, C. L., Cohen, M. R., Wandell, B. A., Newsome, W. T. 2005; 5 (7): 603-621

    Abstract

    Many experimental measurements support the hypothesis that the middle temporal visual area (MT) of the rhesus monkey has a central role in processing visual motion. Most of these studies were performed using luminance stimuli, leaving open the question of how color information is used during motion processing. We investigated the specific question of how S-cone signals, an important source of color information, interact with L,M-cone signals, the dominant source of luminance information. In MT, S-cone-initiated signals combine synergistically with L,M-cone (luminance) signals over most of the stimulus range, regardless of whether the stimuli are added or subtracted. A quantitative analysis of the responses to the combination of S- and L,M-cone signals shows that for a significant minority of cells, these S-cone signals are carried to MT by a color-opponent ("blue-yellow") pathway, such that in certain limited contrast ranges, a small amount of S- and L,M-cone cancellation is observed. Both S- and L,M-cone responses are direction-selective, suggesting that MT processes a wide range of motion signals, including those carried by luminance and color. To investigate this possibility further, we measured MT responses while monkeys discriminated the direction of motion of luminance and S-cone-initiated gratings. The sensitivity of single MT neurons and the correlation between trial-to-trial variations in single neuron firing and perception are similar for S- and L,M-cone stimuli, further supporting a role for MT in processing chromatic motion.

    View details for DOI 10.1167/5.7.1

    View details for Web of Science ID 000232320700001

    View details for PubMedID 16231996

  • Interpreting the BOLD signal ANNUAL REVIEW OF PHYSIOLOGY Logothetis, N. K., Wandell, B. A. 2004; 66: 735-769

    Abstract

    The development of functional magnetic resonance imaging (fMRI) has brought together a broad community of scientists interested in measuring the neural basis of the human mind. Because fMRI signals are an indirect measure of neural activity, interpreting these signals to make deductions about the nervous system requires some understanding of the signaling mechanisms. We describe our current understanding of the causal relationships between neural activity and the blood-oxygen-level-dependent (BOLD) signal, and we review how these analyses have challenged some basic assumptions that have guided neuroscience. We conclude with a discussion of how to use the BOLD signal to make inferences about the neural signal.

    View details for DOI 10.1146/annurev.physiol.66.082602.092845

    View details for Web of Science ID 000220827800028

    View details for PubMedID 14977420

  • Integrated color pixels in 0.18-mu m complementary metal oxide semiconductor technology JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Catrysse, P. B., Wandell, B. A. 2003; 20 (12): 2293-2306

    Abstract

    Following the trend of increased integration in complementary metal oxide semiconductor (CMOS) image sensors, we have explored the potential of implementing light filters by using patterned metal layers placed on top of each pixel's photodetector. To demonstrate wavelength selectivity, we designed and prototyped integrated color pixels in a standard 0.18-microm CMOS technology. Transmittance of several one-dimensional (1D) and two-dimensional (2D) patterned metal layers was measured under various illumination conditions and found to exhibit wavelength selectivity in the visible range. We performed (a) wave optics simulations to predict the spectral responsivity of an uncovered reference pixel and (b) numerical electromagnetic simulations with a 2D finite-difference time-domain method to predict transmittances through 1D patterned metal layers. We found good agreement in both cases. Finally, we used simulations to predict the transmittance for more elaborate designs.

    View details for Web of Science ID 000187024300010

    View details for PubMedID 14686508

  • Long-term deprivation affects visual perception and cortex NATURE NEUROSCIENCE Fine, I., Wade, A. R., Brewer, A. A., May, M. G., Goodman, D. F., Boynton, G. M., Wandell, B. A., MacLeod, D. I. 2003; 6 (9): 915-916

    View details for DOI 10.1038/nn1102

    View details for Web of Science ID 000184970400008

    View details for PubMedID 12937420

  • Spectral estimation theory: beyond linear but before Bayesian JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION DiCarlo, J. M., Wandell, B. A. 2003; 20 (7): 1261-1270

    Abstract

    Most color-acquisition devices capture spectral signals by acquiring only three samples, critically undersampling the spectral information. We analyze the problem of estimating high-dimensional spectral signals from low-dimensional device responses. We begin with the theory and geometry of linear estimation methods. These methods use linear models to characterize the likely input signals and reduce the number of estimation parameters. Next, we introduce two submanifold estimation methods. These methods are based on the observation that for many data sets the deviation between the signal and the linear estimate is systematic; the methods incorporate knowledge of these systematic deviations to improve upon linear estimation methods. We describe the geometric intuition of these methods and evaluate the submanifold method on hyperspectral image data.

    View details for Web of Science ID 000183784000012

    View details for PubMedID 12868632

  • Functional imaging of the visual pathways NEUROLOGIC CLINICS Wandell, B. A., Wade, A. R. 2003; 21 (2): 417-?

    Abstract

    Functional neuroimaging has provided a new view of activity in human visual cortex. There have been a series of interesting developments in understanding the relationship between the functional signals, particularly functional MRI, and basic measurements of action potentials and local field potentials. The new human neuro-imaging measurements have clarified some of the similarities and differences between the general organization of visual areas in human and macaque visual cortex, and there have been some interesting new results concerning cortical visual plasticity and dysfunction. The new fMRI focus on measurements of the human brain will drive new relationships between neurology and visual neuroscience that should help us learn much more about the neural basis of perception.

    View details for DOI 10.1016/S0733-8619(03)00003-3

    View details for Web of Science ID 000183127800004

    View details for PubMedID 12916486

  • Cognitive neuroscience - Overview CURRENT OPINION IN NEUROBIOLOGY Wandell, B. A., Movshon, J. A. 2003; 13 (2): 141-143
  • Visual field representations and locations of visual areas V1/2/3 in human visual cortex JOURNAL OF VISION Dougherty, R. F., Koch, V. M., Brewer, A. A., Fischer, B., Modersitzki, J., Wandell, B. A. 2003; 3 (10): 586-598

    Abstract

    The position, surface area and visual field representation of human visual areas V1, V2 and V3 were measured using fMRI in 7 subjects (14 hemispheres). Cortical visual field maps of the central 12 deg were measured using rotating wedge and expanding ring stimuli. The boundaries between areas were identified using an automated procedure to fit an atlas of the expected visual field map to the data. All position and surface area measurements were made along the boundary between white matter and gray matter. The representation of the central 2 deg of visual field in areas V1, V2, V3 and hV4 spans about 2100 mm2 and is centered on the lateral-ventral aspect of the occipital lobes at Talairach coordinates -29, -78, -11 and 25, -80, -9. The mean area between the 2-deg and 12-deg eccentricities for the primary visual areas was: V1: 1470 mm2; V2: 1115 mm2; and V3: 819 mm2. The sizes of areas V1, V2 and V3 varied by about a factor of 2.5 across individuals; the sizes of V1 and V2 are significantly correlated within individuals, but there is a very low correlation between V1 and V3. These in vivo measurements of normal human retinotopic visual areas can be used as a reference for comparison to unusual cases involving developmental plasticity, recovery from injury, identifying homology with animal models, or analyzing the computational resources available within the visual pathways.

    View details for DOI 10.1167/3.10.1

    View details for Web of Science ID 000223082000001

    View details for PubMedID 14640882

  • Visual areas in macaque cortex measured using functional magnetic resonance imaging JOURNAL OF NEUROSCIENCE Brewer, A. A., Press, W. A., Logothetis, N. K., Wandell, B. A. 2002; 22 (23): 10416-10426

    Abstract

    We describe the first systematic functional magnetic resonance imaging (fMRI) measurements of visual field maps in macaque visual cortex. The boundaries of visual areas V1, V2, V3, V3A, V4, MT/V5, and TEO/V4A were identified using stimuli that create traveling waves of activity in retinotopically organized areas of the visual cortex. Furthermore, these stimuli were used to measure the dimensions of the representations of the central 11 degrees in V1-V3, quantitative visual field eccentricity functions for V1-V3 and MT, and the distribution of foveal and peripheral signals within the occipital lobe. Within areas V1, V2, MT, and portions of V4, the fMRI signals were 5-10 times the noise level (3 mm3 volumes of interest). Signals were weaker but still significant in other cortical regions, including V3, V3A, and TEO. There is good agreement between the fMRI maps and the visual area maps discovered using local anatomical and physiological measurements. The fMRI measurements allow one to obtain a broad view of the distribution of cortical signals, spanning multiple visual areas at a single point in time. The combination of scale and sensitivity demonstrated here create a good foundation for measuring how localized signals and lesions influence the responses and reorganization in widely separated cortical regions. The ability to measure human and macaque maps using the same technology will make it possible to define computational homologies between the two species.

    View details for Web of Science ID 000179458100037

    View details for PubMedID 12451141

  • Chromatic light adaptation measured using functional magnetic resonance imaging JOURNAL OF NEUROSCIENCE Wade, A. R., Wandell, B. A. 2002; 22 (18): 8148-8157

    Abstract

    Sensitivity changes, beginning at the first stages of visual transduction, permit neurons with modest dynamic range to respond to contrast variations across an enormous range of mean illumination. We have used functional magnetic resonance imaging (fMRI) to investigate how these sensitivity changes are controlled within the visual pathways. We measured responses in human visual area V1 to a constant-amplitude, contrast-reversing probe presented on a range of mean backgrounds. We found that signals from probes initiated in the L and M cones were affected by backgrounds that changed the mean absorption rates in the L and M cones, but not by background changes seen only by the S cones. Similarly, signals from S cone-initiated probes were altered by background changes in the S cones, but not by background changes in the L and M cones. Performance in psychophysical tests under similar conditions closely mirrored the changes in V1 fMRI signals. We compare our data with simulations of the visual pathway from photon catch rates to cortical blood-oxygen level-dependent signals and show that the quantitative fMRI signals are consistent with a simple model of mean-field adaptation based on Naka-Rushton (Naka and Rushton, 1966) adaptation mechanisms within cone photoreceptor classes.

    View details for Web of Science ID 000177916000036

    View details for PubMedID 12223569

  • Functional measurements of human ventral occipital cortex: retinotopy and colour PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Wade, A. R., Brewer, A. A., Rieger, J. W., Wandell, B. A. 2002; 357 (1424): 963-973

    Abstract

    Human colour vision originates in the cone photoreceptors, whose spatial density peaks in the fovea and declines rapidly into the periphery. For this reason, one expects to find a large representation of the cone-rich fovea in those cortical locations that support colour perception. Human occipital cortex contains several distinct foveal representations including at least two that extend onto the ventral surface: a region thought to be critical for colour vision. To learn more about these ventral signals, we used functional magnetic resonance imaging to identify visual field maps and colour responsivity on the ventral surface. We found a visual map of the complete contralateral hemifield in a 4 cm(2) region adjacent to ventral V3; the foveal representation of this map is confluent with that of areas V1/2/3. Additionally, a distinct foveal representation is present on the ventral surface situated 3-5 cm anterior from the confluent V1/2/3 foveal representations. This organization is not consistent with the definition of area V8, which assumes the presence of a quarter field representation adjacent to V3v. Comparisons of responses to luminance-matched coloured and achromatic patterns show increased activity to the coloured stimuli beginning in area V1 and extending through the new hemifield representation and further anterior in the ventral occipital lobe.

    View details for DOI 10.1098/rstb.2002.1108

    View details for Web of Science ID 000177902600002

    View details for PubMedID 12217168

  • Optical efficiency of image sensor pixels JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Catrysse, P. B., Wandell, B. A. 2002; 19 (8): 1610-1620

    Abstract

    The ability to reproduce a high-quality image depends strongly on the image sensor light sensitivity. This sensitivity depends, in turn, on the materials, the circuitry, and the optical properties of the pixel. We calculate the optical efficiency of a complementary metal oxide semiconductor (CMOS) image sensor pixel by using a geometrical-optics phase-space approach. We compare the theoretical predictions with measurements made by using a CMOS digital pixel sensor, and we find them to be in agreement within 3%. Finally, we show how to use these optical efficiency calculations to trade off image sensor pixel sensitivity and functionality as CMOS process technology scales.

    View details for Web of Science ID 000177021500017

    View details for PubMedID 12152702

  • Reorganization of human cortical maps caused by inherited photoreceptor abnormalities NATURE NEUROSCIENCE Baseler, H. A., Brewer, A. A., Sharpe, L. T., Morland, A. B., Jagle, H., Wandell, B. A. 2002; 5 (4): 364-370

    Abstract

    We describe a compelling demonstration of large-scale developmental reorganization in the human visual pathways. The developmental reorganization was observed in rod monochromats, a rare group of congenitally colorblind individuals who virtually lack cone photoreceptor function. Normal controls had a cortical region, spanning several square centimeters, that responded to signals initiated in the all-cone foveola but was inactive under rod viewing conditions; in rod monochromats this cortical region responded powerfully to rod-initiated signals. The measurements trace a causal pathway that begins with a genetic anomaly that directly influences sensory cells and ultimately results in a substantial central reorganization.

    View details for DOI 10.1038/nn817

    View details for Web of Science ID 000174606900017

    View details for PubMedID 11914722

  • Abnormal retinotopic representations in human visual cortex revealed by fMRI ACTA PSYCHOLOGICA Morland, A. B., Baseler, H. A., Hoffmann, M. B., Sharpe, L. T., Wandell, B. A. 2001; 107 (1-3): 229-247

    Abstract

    The representation of the visual field in early visual areas is retinotopic. The point-to-point relationship on the retina is therefore maintained on the convoluted cortical surface. Functional magnetic resonance imaging (fMRI) has been able to demonstrate the retinotopic representation of the visual field in occipital cortex of normal subjects. Furthermore, visual areas that are retinotopic can be identified on computationally flattened cortical maps on the basis of positions of the vertical and horizontal meridians. Here, we investigate abnormal retinotopic representations in human visual cortex with fMRI. We present three case studies in which patients with visual disorders are investigated. We have tested a subject who only possesses operating rod photoreceptors. We find in this case that the cortex undergoes a remapping whereby regions that would normally represent central field locations now map more peripheral positions in the visual field: In a human albino we also find abnormal visual cortical activity. Monocular stimulation of each hemifield resulted in activations in the hemisphere contralateral to the stimulated eye. This is consistent with abnormal decussation at the optic chiasm in albinism. Finally, we report a case where a lesion to white matter has resulted in a lack of measurable activity in occipital cortex. The activity was absent for a small region of the visual field, which was found to correspond to the subject's field defect. The cases selected have been chosen to demonstrate the power of fMRI in identifying abnormalities in the cortical representations of the visual field in patients with visual dysfunction. Furthermore, the experiments are able to show how the cortex is capable of modifying the visual field representation in response to abnormal input.

    View details for Web of Science ID 000168792700010

    View details for PubMedID 11388137

  • Visual areas and spatial summation in human visual cortex VISION RESEARCH Press, W. A., Brewer, A. A., Dougherty, R. F., Wade, A. R., Wandell, B. A. 2001; 41 (10-11): 1321-1332

    Abstract

    Functional MRI measurements can securely partition the human posterior occipital lobe into retinotopically organized visual areas (V1, V2 and V3) with experiments that last only 30 min. Methods for identifying functional areas in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact, different laboratories have produced inconsistent reports concerning the visual areas in dorsal and ventral occipital lobe. We report four findings concerning the visual representation in dorsal regions of occipital cortex. First, cortex near area V3A contains a central field representation that is distinct from the foveal representation at the confluence of areas V1, V2 and V3. Second, adjacent to V3A there is a second visual area, V3B, which represents both the upper and lower quadrants. The central representation in V3B appears to merge with that of V3A, much as the central representations of V1/2/3 come together on the lateral margin of the posterior pole. Third, there is yet another dorsal representation of the central visual field. This representation falls in area V7, which includes a representation of both the upper and lower quadrants of the visual field. Fourth, based on visual field and spatial summation measurements, it appears that the receptive field properties of neurons in area V7 differ from those in areas V3A and V3B.

    View details for Web of Science ID 000168565200010

    View details for PubMedID 11322977

  • Scene illuminant classification: brighter is better JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Tominaga, S., Ebisui, S., Wandell, B. A. 2001; 18 (1): 55-64

    Abstract

    Knowledge of the scene illuminant spectral power distribution is useful for many imaging applications, such as color image reproduction and automatic algorithms for image database applications. In many applications accurate spectral characterization of the illuminant is impossible because the input device acquires only three spectral samples. In such applications it is sensible to set a more limited objective of classifying the illuminant as belonging to one of several likely types. We describe a data set of natural images with measured illuminants for testing illuminant classification algorithms. One simple type of algorithm is described and evaluated by using the new data set. The empirical measurements show that illuminant information is more reliable in bright regions than in dark regions. Theoretical predictions of the algorithm's classification performance with respect to scene illuminant blackbody color temperature are tested and confirmed by using the natural-image data set.

    View details for Web of Science ID 000166042500005

    View details for PubMedID 11152004

  • Visualization and measurement of the cortical surface JOURNAL OF COGNITIVE NEUROSCIENCE Wandell, B. A., Chial, S., Backus, B. T. 2000; 12 (5): 739-752

    Abstract

    Much of the human cortical surface is obscured from view by the complex pattern of folds, making the spatial relationship between different surface locations hard to interpret. Methods for viewing large portions of the brain's surface in a single flattened representation are described. The flattened representation preserves several key spatial relationships between regions on the cortical surface. The principles used in the implementations and evaluations of these implementations using artificial test surfaces are provided. Results of applying the methods to structural magnetic resonance measurements of the human brain are also shown. The implementation details are available in the source code, which is freely available on the Internet.

    View details for Web of Science ID 000089817500004

    View details for PubMedID 11054917

  • Perceived speed of colored stimuli NEURON Dougherty, R. F., Press, W. A., Wandell, B. A. 1999; 24 (4): 893-899

    Abstract

    The influence of contrast and color on perceived motion was measured using a speed-matching task. Observers adjusted the speed of an L cone contrast pattern to match that of a variety of colored test patterns. The dependence of speed on test contrast was the same for all test colors measured, differing only by a sensitivity factor. This result suggests that the reduced apparent speed of low contrast targets and certain colored targets is caused by a common cortical mechanism. The cone contrast levels that equate perceived speed differ substantially from those that equate visibility. This result suggests that the neural mechanisms governing speed perception and visibility differ. Perceived speed differences caused by variations in color can be explained by color responses that are characteristic of motion-selective cortex.

    View details for Web of Science ID 000084495300017

    View details for PubMedID 10624952

  • Color signals in area MT of the macaque monkey NEURON Seidemann, E., Poirson, A. B., Wandell, B. A., Newsome, W. T. 1999; 24 (4): 911-917

    Abstract

    The relationship between the neural processing of color and motion information has been a contentious issue in visual neuroscience. We examined this relationship directly by measuring neural responses to isoluminant S cone signals in extrastriate area MT of the macaque monkey. S cone stimuli produced robust, direction-selective responses at most recording sites, indicating that color signals are present in MT. While these responses were unequivocal, S cone contrast sensitivity was, on average, 1.0-1.3 log units lower than luminance contrast sensitivity. The presence of S cone responses and the relative sensitivity of MT neurons to S cone and luminance signals agree with functional magnetic resonance imaging (fMRI) measurements in human MT+. The results are consistent with the hypothesis that color signals in MT influence behavior in speed judgment tasks.

    View details for Web of Science ID 000084495300019

    View details for PubMedID 10624954

  • Color signals in human motion-selective cortex NEURON Wandell, B. A., Poirson, A. B., Newsome, W. T., Baseler, H. A., Boynton, G. M., Huk, A., Gandhi, S., Sharpes, L. T. 1999; 24 (4): 901-909

    Abstract

    The neural basis for the effects of color and contrast on perceived speed was examined using functional magnetic resonance imaging (fMRI). Responses to S cone (blue-yellow) and L + M cone (luminance) patterns were measured in area V1 and in the motion area MT+. The MT+ responses were quantitatively similar to perceptual speed judgments of color patterns but not to color detection measures. We also measured cortical motion responses in individuals lacking L and M cone function (S cone monochromats). The S cone monochromats have clear motion-responsive regions in the conventional MT+ position, and their contrast-response functions there have twice the responsivity of S cone contrast-response functions in normal controls. But, their responsivity is far lower than the normals' responsivity to luminance contrast. Thus, the powerful magnocellular input to MT+ is either weak or silent during photopic vision in S cone monochromats.

    View details for Web of Science ID 000084495300018

    View details for PubMedID 10624953

  • Trichromatic opponent color classification VISION RESEARCH Chichilnisky, E. J., Wandell, B. A. 1999; 39 (20): 3444-3458

    Abstract

    Stimuli varying in intensity and chromaticity, presented on numerous backgrounds, were classified into red/green, blue/yellow and white/black opponent color categories. These measurements revealed the shapes of the boundaries that separate opponent colors in three-dimensional color space. Opponent color classification boundaries were generally not planar, but their shapes could be summarized by a piecewise linear model in which increment and decrement color signals are combined with different weights at two stages to produce opponent color sensations. The effect of background light on classification was largely explained by separate gain changes in increment and decrement cone signals.

    View details for Web of Science ID 000081693700011

    View details for PubMedID 10615508

  • Topographic organization of human visual areas in the absence of input from primary cortex JOURNAL OF NEUROSCIENCE Baseler, H. A., Morland, A. B., Wandell, B. A. 1999; 19 (7): 2619-2627

    Abstract

    Recently, there has been evidence for considerable plasticity in primary sensory areas of adult cortex. In this study, we asked to what extent topographical maps in human extrastriate areas reorganize after damage to a portion of primary visual (striate) cortex, V1. Functional magnetic resonance imaging signals were measured in a subject (G.Y.) with a large calcarine lesion that includes most of primary visual cortex but spares the foveal representation. When foveal stimulation was present, intact cortex in the lesioned occipital lobe exhibited conventional retinotopic organization. Several visual areas could be identified (V1, V2, V3, V3 accessory, and V4 ventral). However, when stimuli were restricted to the blind portion of the visual field, responses were found primarily in dorsal extrastriate areas. Furthermore, cortex that had formerly shown normal topography now represented only the visual field around the lower vertical meridian. Several possible sources for this reorganized activity are considered, including transcallosal connections, direct subcortical projections to extrastriate cortex, and residual inputs from V1 near the margin of the lesion. A scheme is described to explain how the reorganized signals could occur based on changes in the local neural connections.

    View details for Web of Science ID 000079344400020

    View details for PubMedID 10087075

  • Computational neuroimaging of human visual cortex ANNUAL REVIEW OF NEUROSCIENCE Wandell, B. A. 1999; 22: 145-?

    Abstract

    Functional magnetic resonance imaging is a new neuroimaging method for probing the intact, alert, human brain. With this tool, brain activity that has been hidden can now be measured. Recent advances in measuring and understanding human neural responses underlying motion, color, and pattern perception are reviewed. In individual human brain, we can now identify the positions of several retinotopically organized visual areas; measure retinotopic organization within these areas; identify the location of a motion-sensitive region in individual brains; measure responses associated with contrast, color, and motion; and measure effects of attentional modulation on visually evoked responses. By framing experiments and analyses as questions about visual computation, these neuroimaging measurements can be coupled closely with those from other basic vision-science methods.

    View details for Web of Science ID 000079267400007

    View details for PubMedID 10202535

  • Creating connected representations of cortical gray matter for functional MRI visualization IEEE TRANSACTIONS ON MEDICAL IMAGING Teo, P. C., Sapiro, G., Wandell, B. A. 1997; 16 (6): 852-863

    Abstract

    We describe a system that is being used to segment gray matter from magnetic resonance imaging (MRI) and to create connected cortical representations for functional MRI visualization (fMRI). The method exploits knowledge of the anatomy of the cortex and incorporates structural constraints into the segmentation. First, the white matter and cerebral spinal fluid (CSF) regions in the MR volume are segmented using a novel techniques of posterior anisotropic diffusion. Then, the user selects the cortical white matter component of interest, and its structure is verified by checking for cavities and handles. After this, a connected representation of the gray matter is created by a constrained growing-out from the white matter boundary. Because the connectivity is computed, the segmentation can be used as input to several methods of visualizing the spatial pattern of cortical activity within gray matter. In our case, the connected representation of gray matter is used to create a flattened representation of the cortex. Then, fMRI measurements are overlaid on the flattened representation, yielding a representation of the volumetric data within a single image. The software is freely available to the research community.

    View details for Web of Science ID 000072458500015

    View details for PubMedID 9533585

  • Retinotopic organization in human visual cortex and the spatial precision of functional MRI CEREBRAL CORTEX Engel, S. A., Glover, G. H., Wandell, B. A. 1997; 7 (2): 181-192

    Abstract

    A method of using functional magnetic resonance imaging (fMRI) to measure retinotopic organization within human cortex is described. The method is based on a visual stimulus that creates a traveling wave of neural activity within retinotopically organized visual areas. We measured the fMRI signal caused by this stimulus in visual cortex and represented the results on images of the flattened cortical sheet. We used the method to locate visual areas and to evaluate the spatial precision of fMRI. Specifically, we: (i) identified the borders between several retinotopically organized visual areas in the posterior occipital lobe; (ii) measured the function relating cortical position to visual field eccentricity within area V1; (iii) localized activity to within 1.1 mm of visual cortex; and (iv) estimated the spatial resolution of the fMRI signal and found that signal amplitude falls to 60% at a spatial frequency of 1 cycle per 9 mm of visual cortex. This spatial resolution is consistent with a linespread whose full width at half maximum spreads across 3.5 mm of visual cortex.

    View details for Web of Science ID A1997WJ36100009

    View details for PubMedID 9087826

  • Color appearance of mixture gratings VISION RESEARCH Bauml, K. H., Wandell, B. A. 1996; 36 (18): 2849-2864

    Abstract

    We have examined how color appearance varies with spatial pattern. Subjects set color-matches between a uniform, 2 deg matching field and bars within squarewave patterns (1,2 and 4 c/deg) or the superposition of these squarewaves. The matches were set using squarewaves and squarewave mixtures with many different colors and contrasts. The color-matches satisfied the basic properties of a linear system to within a tolerance of twice the precision of repeated matches. Matches satisfied contrast-homogeneity: the contrast of the matching field was proportional to the contrast of the squarewave pattern or the mixture of squarewave patterns. Matches also satisfied pattern-superposition: if a bar in one squarewave matched one uniform field, and a bar in a second squarewave matched a second uniform field, the superposition of the two squarewave bars matched the superposition of the uniform matching fields. Matches are predicted by a model in which the color at a location is predicted by the responses of three linear, pattern-color separable mechanisms. As the individual mechanisms are pattern-color separable, meaningful pattern and color-responsivity functions can be estimated for each of the mechanisms. The estimated color-responsivity functions, based only on asymmetric color-matches, have an opponent-colors organization.

    View details for Web of Science ID A1996VK58400006

    View details for PubMedID 8917788

  • Seeing gray through the ON and OFF pathways VISUAL NEUROSCIENCE Chichilnisky, E. J., Wandell, B. A. 1996; 13 (3): 591-596

    Abstract

    Color appearance judgments revealed fundamental differences in visual processing of incremental and decremental lights. First, the balance of cone activation required for a light to appear achromatic was different for increments and decrements (Judd, 1940; Helson & Michels, 1948). Second, adaptation--the visual system's adjustment to background light--affected achromatic decrements more than increments. Third, the regulation of adaptation for incremental and decremental stimuli depended differently on background signals from the three cone types. We interpret these asymmetries as differences in mechanisms of adaptation in the ON and OFF pathways, and suggest that they evolved to accommodate the range and physical sources of color signals in the two pathways.

    View details for Web of Science ID A1996UH52800020

    View details for PubMedID 8782387

  • Pattern-color separable pathways predict sensitivity to simple colored patterns VISION RESEARCH Poirson, A. B., Wandell, B. A. 1996; 36 (4): 515-526

    Abstract

    We have studied how contrast threshold sensitivity depends jointly on pattern and color. We measured sensitivity to colored Gabor patches from 0.5 to 8 c/deg. At each spatial frequency, we measured in many different color directions. We analyze the sensitivity measurements using a series of nested models. We conclude that a model consisting of three pattern-color separable mechanisms predicts detection performance nearly as well as fitting psychometric functions independently. We derive the pattern and color sensitivities of the separable mechanisms from the experimental data. Two derived mechanisms are spatially lowpass and spectrally color-opponent. The third mechanism is spatially bandpass and spectrally broadband.

    View details for Web of Science ID A1996TU02400003

    View details for PubMedID 8854997

  • PHOTORECEPTOR SENSITIVITY CHANGES EXPLAIN COLOR APPEARANCE SHIFTS INDUCED BY LARGE UNIFORM BACKGROUNDS IN DICHOPTIC MATCHING VISION RESEARCH Chichilnisky, E. J., Wandell, B. A. 1995; 35 (2): 239-254

    Abstract

    Photoreceptor sensitivity changes explained the effect of large uniform backgrounds on the color appearance of small targets in a dichoptic asymmetric color matching experiment. Subjects viewed in each eye a target superimposed on a large background. The backgrounds presented to the two eyes had different spectral compositions. Subjects adjusted the target seen by the right eye to match the appearance of the target seen by the left eye. Receptor sensitivity changes explained the effect of numerous adapting backgrounds on the color appearance of many targets with high precision. Post-receptoral sensitivity changes provided a poorer account of the data. The apparent sensitivity of each receptor class varied inversely with changes in background light absorbed by that receptor class, but did not depend on background light absorbed by the other two receptor classes.

    View details for Web of Science ID A1995QA11800005

    View details for PubMedID 7839619

  • MATCHING COLOR IMAGES - THE EFFECTS OF AXIAL CHROMATIC ABERRATION JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Marimont, D. H., Wandell, B. A. 1994; 11 (12): 3113-3122
  • FMRI OF HUMAN VISUAL-CORTEX NATURE Engel, S. A., Rumelhart, D. E., Wandell, B. A., Lee, A. T., Glover, G. H., Chichilnisky, E. J., Shadlen, M. N. 1994; 369 (6481): 525-525

    View details for Web of Science ID A1994NR29400030

    View details for PubMedID 8031403

  • APPEARANCE OF COLORED PATTERNS - PATTERN COLOR SEPARABILITY JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Poirson, A. B., Wandell, B. A. 1993; 10 (12): 2458-2470

    Abstract

    We have measured how color appearance of square-wave bars varies with stimulus strength and spatial frequency. Observers adjusted the color of a uniform patch to match the color appearance of the bars in square-wave patterns. We used low-to-moderate square-wave patterns, from 1 to 8 cycles per degree (c/deg). The matches are not photoreceptor matches but rather are established at more central neural sites. The signals at the putative central sites obey several simple regularities. The cone contrast of the uniform patch is proportional to square-wave stimulus strength (color homogeneity) and additive with respect to the superposition of equal-frequency square waves containing different colors (color superposition). We use the asymmetric matches to derive, from first principles, three pattern-color-separable appearance pathways. The matches are explained by two spectrally opponent, spatially low-pass mechanisms and one spectrally positive, spatially bandpass mechanism. The spectral mechanisms that we derive are similar to luminance and opponent mechanisms that are derived with entirely different experimental methods.

    View details for Web of Science ID A1993MN61100004

    View details for PubMedID 8301401

  • FUNCTIONAL SEGREGATION OF COLOR AND MOTION PERCEPTION EXAMINED IN MOTION NULLING VISION RESEARCH Chichilnisky, E. J., Heeger, D., Wandell, B. A. 1993; 33 (15): 2113-2125

    Abstract

    We examine two hypotheses about the functional segregation of color and motion perception, using a motion nulling task. The most common interpretation of functional segregation, that motion perception depends only on one of the three dimensions of color, is rejected. We propose and test an alternative formulation of functional segregation: that motion perception depends on a univariate motion signal driven by all three color dimensions, and that the motion signal is determined by the product of the stimulus contrast and a term that depends only on the relative cone excitations. Two predictions of this model are confirmed. First, motion nulling is transitive: when two stimuli null a third they also null another. Second, motion nulling is homogeneous: if two stimuli null one another, they continue to null one another when their contrasts are scaled equally. We describe how to apply our formulation of functional segregation to other behavioral and physiological measurements.

    View details for Web of Science ID A1993LQ40900010

    View details for PubMedID 8266653

  • LINEAR-MODELS OF SURFACE AND ILLUMINANT SPECTRA JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Marimont, D. H., Wandell, B. A. 1992; 9 (11): 1905-1913

    Abstract

    We describe procedures for creating efficient spectral representations for color. The representations generalize conventional tristimulus representations, which are based on the peripheral encoding by the human eye. We use low-dimensional linear models to approximate the spectral properties of surfaces and illuminants with respect to a collection of sensing devices. We choose the linear-model basis functions by minimizing the error in approximating sensor responses for collections of surfaces and illuminants. These linear models offer some conceptual simplifications for applications such as printer calibration; they also perform substantially better than principal-components approximations for computer-graphics applications.

    View details for Web of Science ID A1992JU86800004

    View details for PubMedID 1432341

  • ASYMMETRIC COLOR MATCHING - HOW COLOR APPEARANCE DEPENDS ON THE ILLUMINANT JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Brainard, D. H., Wandell, B. A. 1992; 9 (9): 1433-1448

    Abstract

    We report the results of matching experiments designed to study the color appearance of objects rendered under different simulated illuminants on a CRT monitor. Subjects set asymmetric color matches between a standard object and a test object that were rendered under illuminants with different spectral power distributions. For any illuminant change, we found that the mapping between the cone coordinates of matching standard and test objects was well approximated by a diagonal linear transformation. In this sense, our results are consistent with von Kries's hypothesis [Handb. Physiol. Menschen 3, 109 (1905) [in Sources of Color Vision, D. L. MacAdam, ed. (MIT Press, Cambridge, Mass., 1970)]] that adaptation simply changes the relative sensitivity of the different cone classes. In addition, we examined the dependence of the diagonal transformation on the illuminant change. For the range of illuminants tested, we found that the change in the diagonal elements of the linear transformation was a linear function of the illuminant change.

    View details for Web of Science ID A1992JK70100001

    View details for PubMedID 1527647

  • SURFACE CHARACTERIZATIONS OF COLOR THRESHOLDS JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Poirson, A. B., Wandell, B. A., VARNER, D. C., Brainard, D. H. 1990; 7 (4): 783-789

    Abstract

    We evaluate how well three different parametric shapes, ellipsoids, rectangles, and parallelograms, serve as models of three-dimensional detection contours. We describe how the procedures for deriving the best-fitting shapes constrain inferences about the theoretical visual detection mechanisms. The ellipsoidal shape, commonly assumed by vector-length theories, is related to a class of visual mechanisms that are unique only up to orthogonal transformations. The rectangle shape is related to a unique set of visual mechanisms, but since the rectangle is not invariant with respect to linear transformations the estimated visual mechanisms are dependent on the stimulus coordinate frame. The parallelogram is related to a unique set of visual mechanisms and can be derived by methods that are independent of the stimulus coordinate frame. We evaluate how well these shapes approximate detection contours, using 2-deg test fields with a long (1-sec) Gaussian time course. Two statistical tests suggest that the parallelogram model is too strong. First, we find that the ellipsoid and rectangle shapes fit the data with the same precision as the variance in repeated threshold measurements. The parallelogram model, which has more free parameters, fits the data with more precision than the variance in repeated threshold measurements. Second, although the parallelogram model provides a slightly better fit of our data than the other two shapes, it does not serve as a better guide than the ellipsoidal model for interpolating from the measurements to thresholds in novel color directions.

    View details for Web of Science ID A1990CZ95900027

    View details for PubMedID 2338599

  • TASK-DEPENDENT COLOR DISCRIMINATION JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Poirson, A. B., Wandell, B. A. 1990; 7 (4): 776-782

    Abstract

    When an observer's ability to discriminate colored objects is estimated from the variability in color matches, the observer inspects adjacent visual fields carefully and makes considered judgments. Color discrimination does not always take place under such viewing conditions. When color video displays are used in time-critical applications (e.g., head-up displays, video control panels), the observer must discriminate among briefly presented targets seen within a complex spatial scene. We compare color-discrimination thresholds by using two tasks. In one task the observer makes color matches between two halves of a continuously displayed bipartite field. In a second task the observer detects a color target in a set of briefly presented objects. The data from both tasks are well summarized by ellipsoidal isosensitivity contours. The fitted ellipsoids differ both in their size, which indicates an absolute sensitivity difference, and orientation, which indicates a relative sensitivity difference.

    View details for Web of Science ID A1990CZ95900026

    View details for PubMedID 2338598

  • THE ELLIPSOIDAL REPRESENTATION OF SPECTRAL SENSITIVITY VISION RESEARCH Poirson, A. B., Wandell, B. A. 1990; 30 (4): 647-652

    Abstract

    When plotted in three-dimensional color-space, thresholds of colored lights fall on or near the surface of an ellipsoid. Using data reported in the literature, we estimate the deviation between sets of spectral threshold measurements and the ellipsoid that passes closest to the data. Seventy-three percent of the reported spectral thresholds fall within 0.1 log units of the best-fitting ellipsoid. Our ability to distinguish one ellipsoidal fit as significantly better than another is limited by the choice of sampling directions in color-space. Spectral lights do not provide a good set of sampling directions for reducing the uncertainty about the estimated best-fitting ellipsoid. Complete characterization of visual sensitivity requires measuring thresholds to mixtures of spectral lights.

    View details for Web of Science ID A1990CW16300014

    View details for PubMedID 2339517

  • BLACK LIGHT - HOW SENSORS FILTER SPECTRAL VARIATION OF THE ILLUMINANT IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Brainard, D. H., Wandell, B. A., Cowan, W. B. 1989; 36 (1): 140-149

    Abstract

    Visual sensor responses may be used to classify objects on the basis of their surface reflectance functions. In a color image, the image data are represented as a vector of sensor responses at each point in the image. This vector depends both on the surface reflectance function and on the spectral power distribution of the ambient illumination. Algorithms designed to classify objects on the basis of their surface reflectance functions typically attempt to overcome the dependence of the sensor responses on the illuminant by integrating sensor data collected from multiple surfaces. In machine vision applications, we show that it is often possible to design the sensor spectral responsivities so that the vector direction of the sensor responses does not depend upon the illuminant. We state the conditions under which this is possible and perform an illustrative calculation. In biological systems, where the sensor responsivities are fixed, we show that some changes in the illumination cause no change in the sensor responses. We call such changes in illuminant black illuminants. It is possible to express any illuminant as the sum of two unique components. One component is a black illuminant. We call the second component the visible component. The visible component of an illuminant completely characterizes the effect of the illuminant on the vector of sensor responses.

    View details for Web of Science ID A1989R649100015

    View details for PubMedID 2921060

  • DISCRETE ANALYSIS OF SPATIAL-SENSITIVITY MODELS JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION NIELSEN, K. R., Wandell, B. A. 1988; 5 (5): 743-755

    Abstract

    The visual representation of spatial patterns begins with a series of linear transformations: the stimulus is blurred by the optics, spatially sampled by the photoreceptor array, spatially pooled by the ganglion-cell receptive fields, and so forth. Models of human spatial-pattern vision commonly summarize the initial transformations by a single linear transformation that maps the stimulus into an array of sensor responses. Some components of the initial linear transformations (e.g., lens blurring, photoreceptor sampling) have been estimated empirically; others have not. A computable model must include some assumptions concerning the unknown components of the initial linear encoding. Even a modest sketch of the initial visual encoding requires the specification of a large number of sensors, making the calculations required for performance predictions quite large. We describe procedures for reducing the computational burden of current models of spatial vision that ensure that the simplifications are consistent with the predictions of the complete model. We also describe a method for using pattern-sensitivity measurements to estimate the initial linear transformation. The method is based on the assumption that detection performance is monotonic with the vector length of the sensor responses. We show how contrast-threshold data can be used to estimate the linear transformation needed to characterize threshold performance.

    View details for Web of Science ID A1988N333000014

    View details for PubMedID 3404315

  • THE SYNTHESIS AND ANALYSIS OF COLOR IMAGES IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE Wandell, B. A. 1987; 9 (1): 2-13

    Abstract

    I describe a method for performing the synthesis and analysis of digital color images. The method is based on two principles. First, image data are represented with respect to the separate physical factors, surface reflectance and the spectral power distribution of the ambient light, that give rise to the perceived color of an object. Second, the encoding is made efficient by using a basis expansion for the surface spectral reflectance and spectral power distribution of the ambient light that takes advantage of the high degree of correlation across the visible wavelengths normally found in such functions. Within this framework, the same basic methods can be used to synthesize image data for color display monitors and printed materials, and to analyze image data into estimates of the spectral power distribution and surface spectral reflectances. The method can be applied to a variety of tasks. Examples of applications include the color balancing of color images and the identification of material surface spectral reflectance when the lighting cannot be completely controlled.

    View details for Web of Science ID A1987F378500001

    View details for PubMedID 21869373

  • ANALYSIS OF THE RETINEX THEORY OF COLOR-VISION JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Brainard, D. H., Wandell, B. A. 1986; 3 (10): 1651-1661

    Abstract

    If color appearance is to be a useful feature in identifying an object, then color appearance must remain roughly constant when the object is viewed in different contexts. People maintain approximate color constancy despite variation in the color of nearby objects and despite variation in the spectral power distribution of the ambient light. Land's retinex algorithm is a model of human color constancy. We analyze the retinex algorithm and discuss its general properties. We show that the algorithm is too sensitive to changes in the color of nearby objects to serve as an adequate model of human color constancy.

    View details for Web of Science ID A1986E227800010

    View details for PubMedID 3772627

  • COLOR CONSTANCY - A METHOD FOR RECOVERING SURFACE SPECTRAL REFLECTANCE JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Maloney, L. T., Wandell, B. A. 1986; 3 (1): 29-33

    Abstract

    Human and machine visual sensing is enhanced when surface properties of objects in scenes, including color, can be reliably estimated despite changes in the ambient lighting conditions. We describe a computational method for estimating surface spectral reflectance when the spectral power distribution of the ambient light is not known.

    View details for Web of Science ID A1986AYJ7500006

    View details for PubMedID 3950789

  • COLOR MEASUREMENT AND DISCRIMINATION JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Wandell, B. A. 1985; 2 (1): 62-71

    Abstract

    Theories of color-difference measurement provide a quantitative means for predicting whether two lights will be discriminable to an average observer. Consider the following color-measurement hypothesis. Suppose that two lights evoke responses from the color channels that we write as vectors, U and U'. The vector difference dU = U - U' is itself a set of channel responses that will result from the presentation of some light. I test the hypothesis that U and U' will be discriminable only if the light that gives rise to their differential, dU, is detectable. In the absence of a luminance component in the difference stimulus, dU, the vector-difference hypothesis holds well. In the presence of a luminance component, the theory is clearly false. When a luminance component is present, discrimination judgements depend largely on whether the lights U and U' are in separate, categorical regions of color space.

    View details for Web of Science ID A1985TY04700010

    View details for PubMedID 3968600

  • REACTION-TIMES TO WEAK TEST LIGHTS VISION RESEARCH Wandell, B. A., Ahumada, P., Welsh, D. 1984; 24 (7): 647-652

    Abstract

    Maloney and Wandell [Vision Res. 24, 633-640 (1984)] describe a model of the response of a single visual channel to weak test lights. The initial channel response is a linearly filtered version of the stimulus. The filter output is randomly sampled over time. Each time a sample occurs there is some probability--increasing with the magnitude of the sampled response--that a discrete detection event is generated. Maloney and Wandell derive the statistics of the detection events. In this paper we test the hypothesis that the reaction time responses to the presence of a weak test light are initiated at the first detection event. This permits us to extend the application of the model to lights that are slightly above threshold, but still within the linear operating range of the visual system. We test a parameter-free prediction of the model proposed by maloney and Wandell for lights detected by this statistic. The data are in agreement with the prediction.

    View details for Web of Science ID A1984TB32300003

    View details for PubMedID 6464358

  • A MODEL OF A SINGLE VISUAL CHANNELS RESPONSE TO WEAK TEST LIGHTS VISION RESEARCH Maloney, L. T., Wandell, B. A. 1984; 24 (7): 633-640

    Abstract

    We describe a model of the response of a single visual channel to weak test lights. We assume that the initial channel response may be approximated as a linear filter whose output is sampled at random times. At each sample time there is some probability (increasing with the size of the filter response) that a detection event is generated. The detection events form the basis of the observer's detection and duration discrimination judgments. We derive the statistics of the detection events and empirical tests of the model. Assuming the probability of a detection event to be negligible in the absence of a signal, we derive an exact prediction of the form of the psychometric function for detection. Second, assuming that duration discrimination of weak test lights is based solely on the temporal separation of detection events, we predict the exact form of detection/discrimination performance. Third, assuming that the observer's response is initiated by the first detection event, we derive the form of the cumulative reaction time distribution.

    View details for Web of Science ID A1984TB32300001

    View details for PubMedID 6464356

  • DURATION DISCRIMINATION BETWEEN WEAK TEST LIGHTS VISION RESEARCH Casson, E. J., Wandell, B. A. 1984; 24 (7): 641-645

    Abstract

    Maloney and Wandell [Vision Res. 24, 633-640 (1984)] describe a model of the response of a single visual channel to weak test signals. In the model an initial continuous visual response is randomly sampled, and each sample gives rise--with a probability that increases with the magnitude of the sample--to a discrete detection event. The authors derive a parameter-free prediction for the upper bound on the discriminability of two lights of different durations. In this paper we describe an experimental test of that prediction. We find that the model accurately distinguishes between discrimination performance under conditions where both test lights are detected by a single channel and conditions where the test lights are detected by different channels.

    View details for Web of Science ID A1984TB32300002

    View details for PubMedID 6464357

  • DETECTION DISCRIMINATION IN THE LONG-WAVELENGTH PATHWAYS VISION RESEARCH Wandell, B. A., Sanchez, J., Quinn, B. 1982; 22 (8): 1061-1069

    View details for Web of Science ID A1982PB04700022

    View details for PubMedID 7135844

  • MEASUREMENT OF SMALL COLOR DIFFERENCES PSYCHOLOGICAL REVIEW Wandell, B. A. 1982; 89 (3): 281-302

    View details for Web of Science ID A1982NN36900004

    View details for PubMedID 7100367

  • ADAPTATION IN THE LONG-WAVELENGTH PATHWAYS VISION RESEARCH Wandell, B. A., Welsh, D., Maloney, L. 1982; 22 (8): 1071-1074

    Abstract

    We describe and test predictions of a model of long-wavelength test sensitivity upon large, uniform backgrounds. The model explains changes in sensitivity in the red-green detection pathways strictly based upon losses of sensitivity in the receptors. We derive the prediction that field mixture data for field-mixtures of mu1 (fixed) and an addend, mu 2, must follow the same shape on different intensities of the fixed background, mu 1. This prediction is not in good agreement with the measurements.

    View details for Web of Science ID A1982PB04700023

    View details for PubMedID 7135845

  • DETECTION OF LONG-DURATION, LONG-WAVELENGTH INCREMENTAL FLASHES BY A CHROMATICALLY CODED PATHWAY VISION RESEARCH Wandell, B. A., Pugh, E. N. 1980; 20 (7): 625-636

    View details for Web of Science ID A1980KE29100005

    View details for PubMedID 7434597

  • A FIELD-ADDITIVE PATHWAY DETECTS BRIEF-DURATION, LONG-WAVELENGTH INCREMENTAL FLASHES VISION RESEARCH Wandell, B. A., Pugh, E. N. 1980; 20 (7): 613-624

    View details for Web of Science ID A1980KE29100004

    View details for PubMedID 7434596

  • SPEED-ACCURACY TRADEOFF IN VISUAL DETECTION - APPLICATIONS OF NEURAL COUNTING AND TIMING VISION RESEARCH Wandell, B. A. 1977; 17 (2): 217-225

    View details for Web of Science ID A1977CZ40800008

    View details for PubMedID 867842

  • ANALYSIS OF NERVE SIGNALS DEDUCED FROM METACONTRAST EXPERIMENTS WITH HUMAN OBSERVERS JOURNAL OF PHYSIOLOGY-LONDON Wandell, B. A. 1976; 263 (3): 321-329

    Abstract

    1. This paper reviews Alpern, Rushton & Torii's (1970a-d) derivation of the size of the inhibitory nerve signal arising from after flashes in the metacontrast experiment. 2. Their geometric argument is recast in terms of simple functional equations. This form of argument clearly displays the role of their assumptions in obtaining their main conclusion: nerve signal is linear in intensity over a range of 3-4 log units. 3. Two disadvantages of their approach are discussed. First, it is noted that in the presence of the data the assumption they employ in their analysis is logically equivalent to their conclusion. 4. Secondly, accepting their claim that the nerve signal generated by the after flash is linear over a broad range of intensities, and that this inhibitory signal simply cancels the excitatory signal of the test flash, leads to the conslusion that over this same intensity range the excitatory nerve signal is a power function with an exponent of close to two. This is incompatible with the suggestion that photoreceptor signals have been measured.

    View details for Web of Science ID A1976CV32700001

    View details for PubMedID 1018271

  • COLOR PROPERTIES OF CONTRAST FLASH EFFECT - MONOPTIC VS DICHOPTIC COMPARISONS VISION RESEARCH Yellott, J. I., Wandell, B. A. 1976; 16 (11): 1275-1280

    View details for Web of Science ID A1976CE16900011

    View details for PubMedID 1006999

Conference Proceedings


  • COLOR APPEARANCE - THE EFFECTS OF ILLUMINATION AND SPATIAL PATTERN Wandell, B. A. NATL ACAD SCIENCES. 1993: 9778-9784

    Abstract

    The color we perceive at each point in an image depends on information spread across the three spatial arrays of cone photoreceptors. I describe experiments aimed at clarifying how information is integrated across the spatial arrays to yield a color experience. We have found that changes of color appearance due to changes of the ambient illumination and the pattern's spatial frequency can be described by using a simple set of optical and neural transformations. Each transformation can be thought of as having two parts. First, the transformation converts the color representation into a new coordinate frame that is independent of the image contents. Second, the transformation scales the neural responses in the new coordinate frame by a gain factor that depends on the image contents.

    View details for Web of Science ID A1993MF29600009

    View details for PubMedID 8234314

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