Adam R. Kaiser

Modeling closed‐set phoneme and open‐set word recognition by multi‐channel cochlear implant users

There has been phenomenal growth in research on speech perception by cochlear implant (CI) users since the printing of the ‘‘Bilger Report’’ [Bilger et al., Ann. Otol. Rhinol. Laryngol. 86 (S38), 1–176 (1977)]. Undoubtedly, average speech perception performance with these devices has improved dramatically. However, despite advances in implant technology, CI users continue to demonstrate a wide range in the ability to perceive speech. Little progress has also been made in understanding how CI users actually perceive speech. Although many correlational analyses have been carried out, little research has focused on mechanisms of speech perception, and many clinical decisions are made on a trial‐and‐error basis. Using a new approach, we have developed a quantitative, psychophysically based model (Multidimensional Phoneme Identification, MPI) of phoneme perception by CI users [M. A. Svirsky and T. A. Meyer, J. Acoust. Soc. Am. 103, 2977 (1998)]. The MPI model generates phoneme confusion matrices from performan...

Comparing perception and production vowel spaces of cochlear implant users

This study investigates the relationship between speech production and auditory feedback by comparing vowel production and perception in normal hearing and cochlear implant (CI) using populations. CI users vary greatly in their improvement in speech production after implantation, indicating varying benefit from the CI device. This study examines the degree to which distortions in CI users’ speech can be attributed to perceptual distortions. Three predictions are tested in this study: (1) perceptual distortions will correlate with distortions in speech, (2) there will be a tendency to collapse towards the middle of the vowel space, (3) there will be hyperarticulation of vowels analogous to the Lombard effect. Three measures were used in relation to gender and dialect matched normal hearing subjects: (1) overlap between vowel categories, (2) the distortions of the vowel space centers, (3) vowel space compression. Results indicate that there is little correlation between individual CI users’ spoken vowel spa...

The vowel spaces of normal‐hearing listeners and patients with cochlear implants

Cochlear implant (CI) users show substantial individual differences in their ability to understand speech in general, and vowels in particular. These differences may result from widely different abilities in identifying formant frequencies or in adapting to the more basal than normal spectral information presented by the implant. In this study, we administered a vowel perception test, using a method‐of‐adjustment (MOA) paradigm, to 8 CI users and 43 normal‐hearing listeners. The MOA vowel test consisted of 330 steady‐state synthetic vowel stimuli, varying in F1 and F2, arranged in a visual two‐dimensional grid. Subjects were asked to label and rate on a 7‐point scale those stimuli that matched the vowels contained in ten visually‐presented words, ‘‘heed,’’ ‘‘hid,’’ ‘‘aid,’’ ‘‘head,’’ ‘‘had,’’ ‘‘hut,’’ ‘‘odd,’’ ‘‘whod,’’ ‘‘hood,’’ ‘‘owed,’’ and ‘‘odd.’’ Plots of subjects’ responses for all ten words constituted the vowel spaces of the subjects. With one exception, no systematic shift was observed across all vowel categories of CI users, suggesting that these subjects were able to adapt completely to the spectral shift introduced by the implant. However, the CI users’ spaces differed substantially from normal vowel spaces in terms of the relative size of the vowel categories and their location in perceptual space.

Modeling phoneme and word recognition by adult cochlear implant users: Preliminary report

Conclusions: Bilirubin toxicity produces molecular changes in the expression of CaBPs that relate to impaired calcium homeostasis of specific populations of brain stem auditory neurons. Although the hair ceils in the cochlea are spared from the effects of bilirubin toxicity, their neural innervation is compromised by myelin disruption in the auditory nerve. Clinical Significance: Neonatal hyperbilirubinemia is associated with hearing loss and auditory processing disturbances. The findings in this and previous studies correlate well with the electrophysiological deficits in the auditory brain stem responses and the retrocochlear sensorineural hearing loss that characterize bilirubin toxicity. The findings in this study further implicate bilirubin toxicity as one potential factor in the etiology of auditory neuropathy.

Psychophysical and cognitive limitations to speech perception by cochlear implant users

Deaf listeners with cochlear implants (CIs) achieve significant levels of speech recognition, but their performance range remains wide. Unfortunately, our understanding of the speech perception mechanisms employed by CI users is still incomplete. In particular, we do not know the exact combination of acoustic cues that are employed by CI users to understand speech, nor do we understand how sensory information is represented and combined, and how that information is used to perform speech identification. We have attempted to address this issue by developing mathematical models (Multidimensional Phoneme Identification or MPI models) that aim to predict phoneme identification for individual cochlear implant users based on their discrimination along specified acoustic dimensions. Mathematically, the MPI model is a multidimensional extension of the Durlach–Braida model of loudness perception. The MPI model can explain most of the vowel pairs or consonant pairs that should be more frequently confused by groups ...