Bio

Bio


I received my undergraduate degree in Communication Sciences and Disorders from The Wichita State University. I then traveled to Vanderbilt University to complete a M.S. in Audiology and Hearing Sciences, before completing a clinical fellowship at Henry Ford Hospital in Detroit, MI with Dr. Gary Jacobson. I subsequently completed a Ph.D. at Northwestern University in Communication Disorders with Dr. Beverly Wright exploring patterns of perceptual learning in individuals with normal hearing. Upon completion of my doctorate, I moved to the New York University School of Medicine for a post-doctoral fellowship in the Department of Otolaryngology. There, I worked with Dr. Mario Svirsky to identify recipients of cochlear implants who have not yet fully adapted to their device, and to provide tools which audiologists could use to modify the map to help these patients. I later joined the faculty at NYU, and also at Montclair State University. In 2015 I became the Chief of Audiology at Stanford, where I oversee the Audiology departments of both Stanford Hospital and the Lucille Packard Children’s Hospital.

Academic Appointments


  • Assistant Professor - Med Center Line, Otolaryngology - Head & Neck Surgery Divisions

Professional Education


  • B.A., The Wichita State University, Communication Sciences and Disorders
  • M.S., Vanderbilt University, Audiology and Hearing Sciences
  • Ph.D., Northwestern University, Communication Sciences and Disorders

Research & Scholarship

Current Research and Scholarly Interests


While I have a broad array of research interests, my primary efforts are focused on better understanding the mechanisms by which individuals learn to understand speech or other sounds. I also develop new tools or tests which audiologists can use to maximize outcomes with recipients of cochlear implants. I also investigate methods to facilitate language development in hearing-impaired children. Finally, I am interested in exploring treatments for individuals who suffer from tinnitus.

Teaching

2016-17 Courses


Publications

All Publications


  • Bilateral Loudness Balancing and Distorted Spatial Perception in Recipients of Bilateral Cochlear Implants EAR AND HEARING Fitzgerald, M. B., Kan, A., Goupell, M. J. 2015; 36 (5): E225-E236

    Abstract

    To determine whether bilateral loudness balancing during mapping of bilateral cochlear implants (CIs) produces fused, punctate, and centered auditory images that facilitate lateralization with stimulation on single-electrode pairs.Adopting procedures similar to those that are practiced clinically, direct stimulation was used to obtain most-comfortable levels (C levels) in recipients of bilateral CIs. Three pairs of electrodes, located in the base, middle, and apex of the electrode array, were tested. These electrode pairs were loudness-balanced by playing right-left electrode pairs sequentially. In experiment 1, the authors measured the location, number, and compactness of auditory images in 11 participants in a subjective fusion experiment. In experiment 2, the authors measured the location and number of the auditory images while imposing a range of interaural level differences (ILDs) in 13 participants in a lateralization experiment. Six of these participants repeated the mapping process and lateralization experiment over three separate days to determine the variability in the procedure.In approximately 80% of instances, bilateral loudness balancing was achieved from relatively small adjustments to the C levels (≤3 clinical current units). More important, however, was the observation that in 4 of 11 participants, simultaneous bilateral stimulation regularly elicited percepts that were not fused into a single auditory object. Across all participants, approximately 23% of percepts were not perceived as fused; this contrasts with the 1 to 2% incidence of diplacusis observed with normal-hearing individuals. In addition to the unfused images, the perceived location was often offset from the physical ILD. On the whole, only 45% of percepts presented with an ILD of 0 clinical current units were perceived as fused and heard in the center of the head. Taken together, these results suggest that distortions to the spatial map remain common in bilateral CI recipients even after careful bilateral loudness balancing.The primary conclusion from these experiments is that, even after bilateral loudness balancing, bilateral CI recipients still regularly perceive stimuli that are unfused, offset from the assumed zero ILD, or both. Thus, while current clinical mapping procedures for bilateral CIs are sufficient to enable many of the benefits of bilateral hearing, they may not elicit percepts that are thought to be optimal for sound-source location. As a result, in the absence of new developments in signal processing for CIs, new mapping procedures may need to be developed for bilateral CI recipients to maximize the benefits of bilateral hearing.

    View details for DOI 10.1097/AUD.0000000000000174

    View details for Web of Science ID 000360630800003

    View details for PubMedID 25985017

  • Bilateral cochlear implants with large asymmetries in electrode insertion depth: implications for the study of auditory plasticity ACTA OTO-LARYNGOLOGICA Svirsky, M. A., Fitzgerald, M. B., Sagi, E., Glassman, E. K. 2015; 135 (4): 354-363

    Abstract

    The human frequency-to-place map may be modified by experience, even in adult listeners. However, such plasticity has limitations. Knowledge of the extent and the limitations of human auditory plasticity can help optimize parameter settings in users of auditory prostheses.To what extent can adults adapt to sharply different frequency-to-place maps across ears? This question was investigated in two bilateral cochlear implant users who had a full electrode insertion in one ear, a much shallower insertion in the other ear, and standard frequency-to-electrode maps in both ears.Three methods were used to assess adaptation to the frequency-to-electrode maps in each ear: (1) pitch matching of electrodes in opposite ears, (2) listener-driven selection of the most intelligible frequency-to-electrode map, and (3) speech perception tests. Based on these measurements, one subject was fitted with an alternative frequency-to-electrode map, which sought to compensate for her incomplete adaptation to the standard frequency-to-electrode map.Both listeners showed remarkable ability to adapt, but such adaptation remained incomplete for the ear with the shallower electrode insertion, even after extended experience. The alternative frequency-to-electrode map that was tested resulted in substantial increases in speech perception for one subject in the short insertion ear.

    View details for DOI 10.3109/00016489.2014.1002052

    View details for Web of Science ID 000351365500007

    View details for PubMedID 25719506

  • Feasibility of Real-Time Selection of Frequency Tables in an Acoustic Simulation of a Cochlear Implant EAR AND HEARING Fitzgerald, M. B., Sagi, E., Morbiwala, T. A., Tan, C., Svirsky, M. A. 2013; 34 (6): 763-772

    Abstract

    Perception of spectrally degraded speech is particularly difficult when the signal is also distorted along the frequency axis. This might be particularly important for post-lingually deafened recipients of cochlear implants (CIs), who must adapt to a signal where there may be a mismatch between the frequencies of an input signal and the characteristic frequencies of the neurons stimulated by the CI. However, there is a lack of tools that can be used to identify whether an individual has adapted fully to a mismatch in the frequency-to-place relationship and if so, to find a frequency table that ameliorates any negative effects of an unadapted mismatch. The goal of the proposed investigation is to test the feasibility of whether real-time selection of frequency tables can be used to identify cases in which listeners have not fully adapted to a frequency mismatch. The assumption underlying this approach is that listeners who have not adapted to a frequency mismatch will select a frequency table that minimizes any such mismatches, even at the expense of reducing the information provided by this frequency table.Thirty-four normal-hearing adults listened to a noise-vocoded acoustic simulation of a CI and adjusted the frequency table in real time until they obtained a frequency table that sounded "most intelligible" to them. The use of an acoustic simulation was essential to this study because it allowed the authors to explicitly control the degree of frequency mismatch present in the simulation. None of the listeners had any previous experience with vocoded speech, in order to test the hypothesis that the real-time selection procedure could be used to identify cases in which a listener has not adapted to a frequency mismatch. After obtaining a self-selected table, the authors measured consonant nucleus consonant word-recognition scores with that self-selected table and two other frequency tables: a "frequency-matched" table that matched the analysis filters with the noisebands of the noise-vocoder simulation, and a "right information" table that is similar to that used in most CI speech processors, but in this simulation results in a frequency shift equivalent to 6.5 mm of cochlear space.Listeners tended to select a table that was very close to, but shifted slightly lower in frequency from the frequency-matched table. The real-time selection process took on average 2 to 3 min for each trial, and the between-trial variability was comparable with that previously observed with closely related procedures. The word-recognition scores with the self-selected table were clearly higher than with the right-information table and slightly higher than with the frequency-matched table.Real-time self-selection of frequency tables may be a viable tool for identifying listeners who have not adapted to a mismatch in the frequency-to-place relationship, and to find a frequency table that is more appropriate for them. Moreover, the small but significant improvements in word-recognition ability observed with the self-selected table suggest that these listeners based their selections on intelligibility rather than some other factor. The within-subject variability in the real-time selection procedure was comparable with that of a genetic algorithm, and the speed of the real-time procedure appeared to be faster than either a genetic algorithm or a simplex procedure.

    View details for Web of Science ID 000330361200011

    View details for PubMedID 23807089

  • Factors influencing consistent device use in pediatric recipients of bilateral cochlear implants. Cochlear implants international Fitzgerald, M. B., Green, J. E., Fang, Y., Waltzman, S. B. 2013; 14 (5): 257-265

    Abstract

    To determine which demographic or performance variables are associated with inconsistent use of a second implant in pediatric recipients of sequential bilateral cochlear implants (CIs).A retrospective chart review was conducted on pediatric recipients of sequential bilateral CIs. Children were divided into two age groups, 5-9 and 10-17 years of age. For each group, we examined whether inconsistent use of the second implant (CI-2) was associated with a variety of demographic variables, or speech-perception scores.In children aged 5-9 years, inconsistent use of CI-2 was not significantly associated with any demographic variable, but was related to both the word-recognition score with CI-2, and the difference in word-recognition scores between the first implant (CI-1) and CI-2. In children aged 10-17 years, these relationships were not significant due to smaller number of subjects. Finally, CI-2 word-recognition scores across all children were significantly correlated with the age of implantation for both CI-1 and CI-2, and the time between CI-1 and CI-2 surgeries.Speech-recognition scores obtained with CI-2, and the extent to which it differs from CI-1, are most closely related with inconsistent use of CI-2 in pediatric sequential implantees. These results are consistent with similar data previously reported by other investigators. While children implanted with CI-2 at a later age generally perform more poorly, most children still use both implants, and benefit from CI-2 even when receiving the implant as an adolescent.In pediatric recipients of sequential bilateral CIs, inconsistent use of CI-2 is related to the speech recognition scores with CI-2, and the difference in speech-recognition scores between CI-1 and CI-2. In addition, speech-recognition scores with CI-2 are related to the amount of time between CI-1 and CI-2 surgeries, and the age of implantation for both CI-1 and CI-2.

    View details for DOI 10.1179/1754762812Y.0000000026

    View details for PubMedID 23510638

  • Perceptual learning and generalization resulting from training on an auditory amplitude-modulation detection task JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA Fitzgerald, M. B., Wright, B. A. 2011; 129 (2): 898-906

    Abstract

    Fluctuations in sound amplitude provide important cues to the identity of many sounds including speech. Of interest here was whether the ability to detect these fluctuations can be improved with practice, and if so whether this learning generalizes to untrained cases. To address these issues, normal-hearing adults (n = 9) were trained to detect sinusoidal amplitude modulation (SAM; 80-Hz rate, 3-4 kHz bandpass carrier) 720 trials/day for 6-7 days and were tested before and after training on related SAM-detection and SAM-rate-discrimination conditions. Controls (n = 9) only participated in the pre- and post-tests. The trained listeners improved more than the controls on the trained condition between the pre- and post-tests, but different subgroups of trained listeners required different amounts of practice to reach asymptotic performance, ranging from 1 (n = 6) to 4-6 (n = 3) sessions. This training-induced learning did not generalize to detection with two untrained carrier spectra (5 kHz low-pass and 0.5-1.5 kHz bandpass) or to rate discrimination with the trained rate and carrier spectrum, but there was some indication that it generalized to detection with two untrained rates (30 and 150 Hz). Thus, practice improved the ability to detect amplitude modulation, but the generalization of this learning to untrained cases was somewhat limited.

    View details for DOI 10.1121/1.3531841

    View details for Web of Science ID 000287709700038

    View details for PubMedID 21361447

  • A New Software Tool to Optimize Frequency Table Selection for Cochlear Implants OTOLOGY & NEUROTOLOGY Jethanamest, D., Tan, C., Fitzgerald, M. B., Svirsky, M. A. 2010; 31 (8): 1242-1247

    Abstract

    When cochlear implant (CI) users are allowed to self-select the "most intelligible" frequency-to-electrode table, some of them choose one that differs from the default frequency table that is normally used in clinical practice.CIs reproduce the tonotopicity of normal cochleas using frequency-to-electrode tables that assign stimulation of more basal electrodes to higher frequencies and more apical electrodes to lower frequency sounds. Current audiologic practice uses a default frequency-to-electrode table for most patients. However, individual differences in cochlear size, neural survival, and electrode positioning may result in different tables sounding most intelligible to different patients. No clinical tools currently exist to facilitate this fitting.A software tool was designed that enables CI users to self-select a most intelligible frequency table. Users explore a 2-dimensional space that represents a range of different frequency tables. Unlike existing tools, this software enables users to interactively audition speech processed by different frequency tables and quickly identify a preferred one. Pilot testing was performed in 11 long-term, postlingually deaf CI users.The software tool was designed, developed, tested, and debugged. Patients successfully used the tool to sample frequency tables and to self-select tables deemed most intelligible, which for approximately half of the users differed from the clinical default.A software tool allowing CI users to self-select frequency-to-electrode tables may help in fitting postlingually deaf users. This novel approach may transform current methods of CI fitting.

    View details for DOI 10.1097/MAO.0b013e3181f2063e

    View details for Web of Science ID 000282306900013

    View details for PubMedID 20729774

  • Enhancing Perceptual Learning by Combining Practice with Periods of Additional Sensory Stimulation JOURNAL OF NEUROSCIENCE Wright, B. A., Sabin, A. T., Zhang, Y., Marrone, N., Fitzgerald, M. B. 2010; 30 (38): 12868-12877

    Abstract

    Perceptual skills can be improved even in adulthood, but this learning seldom occurs by stimulus exposure alone. Instead, it requires considerable practice performing a perceptual task with relevant stimuli. It is thought that task performance permits the stimuli to drive learning. A corresponding assumption is that the same stimuli do not contribute to improvement when encountered separately from relevant task performance because of the absence of this permissive signal. However, these ideas are based on only two types of studies, in which the task was either always performed or not performed at all. Here we demonstrate enhanced perceptual learning on an auditory frequency-discrimination task in human listeners when practice on that target task was combined with additional stimulation. Learning was enhanced regardless of whether the periods of additional stimulation were interleaved with or provided exclusively before or after target-task performance, and even though that stimulation occurred during the performance of an irrelevant (auditory or written) task. The additional exposures were only beneficial when they shared the same frequency with, though they did not need to be identical to, those used during target-task performance. Their effectiveness also was diminished when they were presented 15 min after practice on the target task and was eliminated when that separation was increased to 4 h. These data show that exposure to an acoustic stimulus can facilitate learning when encountered outside of the time of practice on a perceptual task. By properly using additional stimulation one may markedly improve the efficiency of perceptual training regimens.

    View details for DOI 10.1523/JNEUROSCI.0487-10.2010

    View details for Web of Science ID 000282097600030

    View details for PubMedID 20861390

  • Reimplantation of hybrid cochlear implant users with a full-length electrode after loss of residual hearing OTOLOGY & NEUROTOLOGY Fitzgerald, M. B., Sagi, E., Jackson, M., Shapiro, W. H., Roland, J. T., Waltzman, S. B., Svirsky, M. A. 2008; 29 (2): 168-173

    Abstract

    To assess word recognition and pitch-scaling abilities of cochlear implant users first implanted with a Nucleus 10-mm Hybrid electrode array and then reimplanted with a full length Nucleus Freedom array after loss of residual hearing.Although electroacoustic stimulation is a promising treatment for patients with residual low-frequency hearing,a small subset of them lose that residual hearing. It is not clear whether these patients would be better served by leaving in the 10-mm array and providing electric stimulation through it, or by replacing it with a standard full-length array.Word recognition and pitch-scaling abilities were measured in 2 users of hybrid cochlear implants who lost their residual hearing in the implanted ear after a few months. Tests were repeated over several months, first with a 10-mm array, and after, these patients were reimplanted with a full array. The word recognition task consisted of 2 50-word consonant nucleus consonant (CNC) lists. In the pitch-scaling task, 6 electrodes were stimulated in pseudorandom order, and patients assigned a pitch value to the sensation elicited by each electrode.Shortly after reimplantation with the full electrode array, speech understanding was much better than with the 10-mm array. Patients improved their ability to perform the pitch-scaling task over time with the full array, although their performance on that task was variable, and the improvements were often small.1) Short electrode arrays may help preserve residual hearing but may also provide less benefit than traditional cochlear implants for some patients. 2) Pitch percepts in response to electric stimulation may be modified by experience.

    View details for Web of Science ID 000252840700012

    View details for PubMedID 18165793

  • What matched comparisons can and cannot tell us: The case of cochlear implants EAR AND HEARING Sagi, E., Fitzgerald, M. B., Svirsky, M. A. 2007; 28 (4): 571-579

    Abstract

    To examine the conclusions and possible misinterpretations that may or may not be drawn from the "outcome-matching method," a study design recently used in the cochlear implant literature. In this method, subject groups are matched not only on potentially confounding variables but also on an outcome measure that is closely related to the outcome measure under analysis. For example, subjects may be matched according to their speech perception scores in quiet, and their speech perception in noise is compared.The present study includes two components, a simulation study and a questionnaire. In the simulation study, the outcome-matching method was applied to pseudo-randomly generated data. Simulated speech perception scores in quiet and in noise were generated for two comparison groups, in two imaginary worlds. In both worlds, comparison group A performed only slightly worse in noise than in quiet, whereas comparison group B performed significantly worse in noise than in quiet. In Imaginary World 1, comparison group A had better speech perception scores than comparison group B. In Imaginary World 2, comparison group B had better speech perception scores than comparison group A. The outcome-matching method was applied to these data twice in each imaginary world: 1) matching scores in quiet and comparing in noise, and 2) matching scores in noise and comparing in quiet. This procedure was repeated 10,000 times. The second part of the study was conducted to address the level of misinterpretation that could arise from the outcome-matching method. A questionnaire was administered to 54 students in a senior level course on speech and hearing to assess their opinions about speech perception with two different models of cochlear implant devices. The students were instructed to fill out the questionnaire before and after reading a paper that used the outcome-matching method to examine speech perception in noise and in quiet with those two cochlear implant devices.When pseudorandom scores were matched in quiet, comparison group A's scores in noise were significantly better than comparison group B's scores. Results were different when scores were matched in noise: in this case, comparison group B's scores in quiet were significantly better than comparison group A's scores. Thus, the choice of outcome measure used for matching determined the result of the comparison. Additionally, results of the comparisons were identical regardless of whether they were conducted using data from Imaginary World 1 (where comparison group A is better) or from Imaginary World 2 (where comparison group B is better). After reading the paper that used the outcome-matching method, students' opinions about the two cochlear implants underwent a significant change even though, according to the simulation study, this opinion change was not warranted by the data.The outcome-matching method can provide important information about differences within a comparison group, but it cannot be used to determine whether a given device or clinical intervention is better than another one. Care must be used when interpreting the results of a study using the outcome-matching method.

    View details for Web of Science ID 000247829000012

    View details for PubMedID 17609617

  • The effect of perimodiolar placement on speech perception and frequency discrimination by cochlear implant users ACTA OTO-LARYNGOLOGICA Fitzgerald, M. B., Shapiro, W. H., McDonald, P. D., Neuburger, H. S., Ashburn-Reed, S., Immerman, S., Jethanamest, D., Roland, J. T., Svirsky, M. A. 2007; 127 (4): 378-383

    Abstract

    Neither speech understanding nor frequency discrimination ability was better in Nucleus Contour users than in Nucleus 24 straight electrode users. Furthermore, perimodiolar electrode placement does not result in better frequency discrimination.We addressed three questions related to perimodiolar electrode placement. First, do patients implanted with the Contour electrode understand speech better than with an otherwise identical device that has a straight electrode? Second, do these groups have different frequency discrimination abilities? Third, is the distance of the electrode from the modiolus related to frequency discrimination ability?Contour and straight electrode users were matched on four important variables. We then tested these listeners on CNC word and HINT sentence identification tasks, and on a formant frequency discrimination task. We also examined X-rays and measured the distance of the electrodes from the modiolus to determine whether there is a relationship between this factor and frequency discrimination ability.Both speech understanding and frequency discrimination abilities were similar for listeners implanted with the Contour vs a straight electrode. Furthermore, there was no linear relationship between electrode-modiolus distance and frequency discrimination ability. However, we did note a second-order relationship between these variables, suggesting that frequency discrimination is worse when the electrodes are either too close or too far away from the modiolus.

    View details for DOI 10.1080/00016480701258671

    View details for Web of Science ID 000246298700007

    View details for PubMedID 17453457

  • Perceptual-learning evidence for separate processing of asynchrony and order tasks JOURNAL OF NEUROSCIENCE Mossbridge, J. A., Fitzgerald, M. B., O'Connor, E. S., Wright, B. A. 2006; 26 (49): 12708-12716

    Abstract

    Normal perception depends, in part, on accurate judgments of the temporal relationships between sensory events. Two such relative-timing skills are the ability to detect stimulus asynchrony and to discriminate stimulus order. Here we investigated the neural processes contributing to the performance of auditory asynchrony and order tasks in humans, using a perceptual-learning paradigm. In each of two parallel experiments, we tested listeners on a pretest and a posttest consisting of auditory relative-timing conditions. Between these two tests, we trained a subset of listeners approximately 1 h/d for 6-8 d on a single relative-timing condition. The trained listeners practiced asynchrony detection in one experiment and order discrimination in the other. Both groups were trained at sound onset with tones at 0.25 and 4.0 kHz. The remaining listeners in each experiment, who served as controls, did not receive multihour training during the 8-10 d between the pretest and posttest. These controls improved even without intervening training, adding to evidence that a single session of exposure to perceptual tasks can yield learning. Most importantly, each of the two groups of trained listeners learned more on their respective trained conditions than controls, but this learning occurred only on the two trained conditions. Neither group of trained listeners generalized their learning to the other task (order or asynchrony), an untrained temporal position (sound offset), or untrained frequency pairs. Thus, it appears that multihour training on relative-timing skills affects task-specific neural circuits that are tuned to a given temporal position and combination of stimulus components.

    View details for DOI 10.1523/JNEUROSCI.2254-06.2006

    View details for Web of Science ID 000242626100011

    View details for PubMedID 17151274

  • Customized selection of frequency maps in an acoustic simulation of a cochlear implant. Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference Fitzgerald, M. B., Morbiwala, T. A., Svirsky, M. A. 2006; 1: 3596-3599

    Abstract

    Cochlear implants can restore hearing to deaf individuals by electrically stimulating the auditory nerve. They do so by assigning different frequencies to different stimulating electrodes via a frequency map. We have developed a device that enables us to change the frequency map in real time. Here, in normal-hearing adults listening to an acoustic simulation of a cochlear implant, we investigate what frequency maps are initially preferred, and how the ability to understand speech with that preferred map compares with two other maps. We show that naive listeners prefer a map that balances the need for low-frequency information with the desire for a naturally-sounding stimulus, and that initial performance with this listener-selected map is better than that with a map that distorts the signal to provide low-frequency information.

    View details for PubMedID 17946188

  • A perceptual learning investigation of the pitch elicited by amplitude-modulated noise JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA Fitzgerald, M. B., Wright, B. A. 2005; 118 (6): 3794-3803

    Abstract

    Noise that is amplitude modulated at rates ranging from 40 to 850 Hz can elicit a sensation of pitch. Here, the processing of this temporally based pitch was investigated using a perceptual-learning paradigm. Nine listeners were trained (1 hour per day for 6-8 days) to discriminate a standard rate of sinusoidal amplitude modulation (SAM) from a faster rate in a single condition (150 Hz SAM rate, 5 kHz low-pass carrier). All trained listeners improved significantly on that condition. These trained listeners subsequently showed no more improvement than nine untrained controls on pure-tone and rippled-noise discrimination with the same pitch, and on SAM-rate discrimination with a 30 Hz rate, although they did show some improvement with a 300 Hz rate. In addition, most trained, but not control, listeners were worse at detecting SAM at 150 Hz after, compared to before training. These results indicate that listeners can learn to improve their ability to discriminate SAM rate with multiple-hour training and that the mechanism that is modified by learning encodes (1) the pitch of SAM noise but not that of pure tones and rippled noise, (2) different SAM rates separately, and (3) differences in SAM rate more effectively than cues for SAM detection.

    View details for DOI 10.1121/1.2074687

    View details for Web of Science ID 000234101000042

    View details for PubMedID 16419824

  • The time course of attention in a simple auditory detection task PERCEPTION & PSYCHOPHYSICS Wright, B. A., Fitzgerald, M. B. 2004; 66 (3): 508-516

    Abstract

    What is the time course of human attention in a simple auditory detection task? To investigate this question, we determined the detectability of a 20-msec, 1000-Hz tone presented at expected and unexpected times. Twelve listeners who expected the tone to occur at a specific time after a 300-msec narrowband noise rarely detected signals presented 150-375 msec before or 100-200 msec after that expected time. The shape of this temporal-attention window depended on the expected presentation time of the tone and the temporal markers available in the trials. Further, though expecting the signal to occur in silence, listeners often detected signals presented at unexpected times during the noise. Combined with previous data, these results further clarify the listening strategy humans use when trying to detect an expected sound: Humans seem to listen specifically for that sound, while ignoring the background in which it is presented, around the time when the sound is expected to occur.

    View details for Web of Science ID 000222163300013

    View details for PubMedID 15283074

  • Different patterns of human discrimination learning for two interaural cues to sound-source location PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Wright, B. A., Fitzgerald, M. B. 2001; 98 (21): 12307-12312

    Abstract

    Two of the primary cues used to localize the sources of sounds are interaural level differences (ILDs) and interaural time differences (ITDs). We conducted two experiments to explore how practice affects the human discrimination of values of ILDs and ongoing ITDs presented over headphones. We measured discrimination thresholds of 13 to 32 naive listeners in a variety of conditions during a pretest and again, 2 weeks later, during a posttest. Between those two tests, we trained a subset of listeners 1 h per day for 9 days on a single ILD or ITD condition. Listeners improved on both ILD and ITD discrimination. Improvement was initially rapid for both cue types and appeared to generalize broadly across conditions, indicating conceptual or procedural learning. A subsequent slower-improvement stage, which occurred solely for the ILD cue, only affected conditions with the trained stimulus frequency, suggesting that stimulus processing had fundamentally changed. These different learning patterns indicate that practice affects the attention to, or low-level encoding of, ILDs and ITDs at sites at which the two cue types are processed separately. Thus, these data reveal differences in the effect of practice on ILD and ITD discrimination, and provide insight into the encoding of these two cues to sound-source location in humans.

    View details for Web of Science ID 000171558900087

    View details for PubMedID 11593048