Faculty Bibliography

The Laboratory of Translational Auditory Research (LTAR/NYUSM) is part of the Department of Otolaryngology at the New York University School of Medicine and has close ties to the New York University Cochlear Implant Center. LTAR investigators have expertise in multiple related disciplines including speech and hearing science, audiology, engineering, and physiology. The lines of research in the laboratory deal mostly with speech perception by hearing impaired listeners, and particularly those who use cochlear implants (CIs) or hearing aids (HAs). Although the laboratory's research interests are diverse, there are common threads that permeate and tie all of its work. In particular, a strong interest in translational research underlies even the most basic studies carried out in the laboratory. Another important element is the development of engineering and computational tools, which range from mathematical models of speech perception to software and hardware that bypass clinical speech processors and stimulate cochlear implants directly, to novel ways of analyzing clinical outcomes data. If the appropriate tool to conduct an important experiment does not exist, we may work to develop it, either in house or in collaboration with academic or industrial partners. Another notable characteristic of the laboratory is its interdisciplinary nature where, for example, an audiologist and an engineer might work closely to develop an approach that would not have been feasible if each had worked singly on the project. Similarly, investigators with expertise in hearing aids and cochlear implants might join forces to study how human listeners integrate information provided by a CI and a HA. The following pages provide a flavor of the diversity and the commonalities of our research interests.

This study investigated which acoustic cues within the speech signal are responsible for bimodal speech perception benefit. Seven cochlear implant (CI) users with usable residual hearing at low frequencies in the non-implanted ear participated. Sentence tests were performed in near-quiet (some noise on the CI side to reduce scores from ceiling) and in a modulated noise background, with the implant alone and with the addition, in the hearing ear, of one of four types of acoustic signals derived from the same sentences: (1) a complex tone modulated by the fundamental frequency (F0) and amplitude envelope contours; (2) a pure tone modulated by the F0 and amplitude contours; (3) a noise-vocoded signal; (4) unprocessed speech. The modulated tones provided F0 information without spectral shape information, whilst the vocoded signal presented spectral shape information without F0 information. For the group as a whole, only the unprocessed speech condition provided significant benefit over implant-alone scores, in both near-quiet and noise. This suggests that, on average, F0 or spectral cues in isolation provided limited benefit for these subjects in the tested listening conditions, and that the significant benefit observed in the full-signal condition was derived from implantees' use of a combination of these cues.

This study examines behavioral and physiological measures of pitch matching in cochlear implant (CI) users who have residual hearing in the contralateral ear. Subjects adjusted the frequency of an acoustic tone to match the pitch percept elicited by electrical stimulation in the other ear, when stimulation was alternating across two ears. In general, the selected acoustic frequencies did not line up perfectly with the center frequencies of the analysis bands corresponding to each stimulation electrode. Similar alternating electro-acoustic stimuli were used to record Auditory Evoked Potentials on 8 NH subjects and 3 CI patients. NH subjects were presented with a fixed tone in one ear, while tones in the other ear varied within a few octaves from the fixed tone. CI patients were stimulated with six different audible tones including their pitch-matched tones, while receiving electrical stimulation in the electrode. N1 latency for NH subjects was minimized when the same frequency was presented to both ears. Similarly, N1 latency for CI patients who are able to pitch match was minimized when the tone was at the pitch matched frequency of the stimulated electrode. These results suggest that N1 latency can be a possible objective measure of pitch matching. (Work supported by NIH/NIDCD 1K25DC010834-01;PI:Tan, PSC-CUNY;PI:Martin, and NIH/NIDCD R01-DC03937;PI:Svirsky.).

A novel psychophysical method was developed for assessing spatial resolution in cochlear implants. Spectrally flat and spectrally peaked pulse train stimuli were generated by interleaving pulses on 11 electrodes. Spectrally flat stimuli used loudness-balanced currents and the spectrally peaked stimuli had a single spatial ripple with the current of the middle electrode raised to create a peak while the currents on two electrodes equally spaced at variable distance from the peak electrode were reduced to create valleys. The currents on peak and valley electrodes were adjusted to balance the overall loudness with the spectrally flat stimulus, while keeping the currents on flanking electrodes fixed. The psychometric functions obtained from percent correct discrimination of peaked and flat stimuli versus the distance between peak and valley electrodes were used to quantify spatial resolution for each of the eight subjects. The ability to resolve the spatial ripple correlated strongly with current level difference limens measured on the peak electrode. The results were consistent with a hypothesis that a factor other than spread of excitation (such as neural response variance) might underlie much of the variability in spatial resolution. Resolution ability was not correlated with phoneme recognition in quiet or sentence recognition in quiet and background noise, consistent with a hypothesis that implantees rely on cues other than fine spectral detail to identify speech, perhaps because this detail is poorly accessible or unreliable.

The multidimensional phoneme identification model is applied to consonant confusion matrices obtained from 28 postlingually deafened cochlear implant users. This model predicts consonant matrices based on these subjects' ability to discriminate a set of postulated spectral, temporal, and amplitude speech cues as presented to them by their device. The model produced confusion matrices that matched many aspects of individual subjects' consonant matrices, including information transfer for the voicing, manner, and place features, despite individual differences in age at implantation, implant experience, device and stimulation strategy used, as well as overall consonant identification level. The model was able to match the general pattern of errors between consonants, but not the full complexity of all consonant errors made by each individual. The present study represents an important first step in developing a model that can be used to test specific hypotheses about the mechanisms cochlear implant users employ to understand speech

A portable real-time speech processor that implements an acoustic simulation model of a cochlear implant (CI) has been developed on the Apple iPhone / iPod Touch to permit testing and experimentation under extended exposure in real-world environments. This simulator allows for both a variable number of noise band channels and electrode insertion depth. Utilizing this portable CI simulator, we tested perceptual learning in normal hearing listeners by measuring word and sentence comprehension behaviorally before and after 2 weeks of exposure. To evaluate changes in neural activation related to adaptation to transformed speech, fMRI was also conducted. Differences in brain activation after training occurred in the inferior frontal gyrus and areas related to language processing. A 15-20% improvement in word and sentence comprehension of cochlear implant simulated speech was also observed. These results demonstrate the effectiveness of a portable CI simulator as a research tool and provide new information about the physiological changes that accompany perceptual learning of degraded auditory input.

HYPOTHESIS: 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. BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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

OBJECTIVE: To investigate whether children implanted in the first year of life show higher levels of speech perception than later-implanted children, when compared at the same ages and to investigate the time course of sensitive periods for developing speech perception skills. More specifically, to determine whether faster gains in speech perception are made by children implanted before 1 year old relative to those implanted at 2 or 3 years. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary academic referral center. PATIENTS: 117 children with congenital profound bilateral sensorineural hearing loss, with no additional identified disabilities. INTERVENTION: Cochlear implantation in the first, second, or third year of life. MAIN OUTCOME MEASURE: Development curves showing Lexical Neighborhood Test (LNT) word identification scores as a function of age. RESULTS: Children implanted within the first year of life have a mean advantage of 8.2% LNT-easy word scores over those implanted in the second year (p < 0.001) and a 16.8% advantage in LNT-easy word scores over those implanted in the third year of life (p < 0.001). These advantages remained statistically significant after accounting for sex, residual hearing, and bilateral cochlear implant use. When speech perception scores were expressed as a function of 'hearing age' rather than chronological age, however, there were no significant differences among the 3 groups. CONCLUSION: There is a clear speech perception advantage for earlier-implanted children over later-implanted children when compared at the same age but not when compared at the same time after implantation. Thus, the sensitive period for developing word identification seems to extend at least until age 3 years