Faculty Bibliography

A method is presented for analyzing cochlear implant stimulations and typical representations used in simulations. Filtered "white-noise" bands are modulated using sinusoids, representing differing stimulation channels. These representations, along with their corresponding envelopes, are used to generate neural activation patterns (NAPs), which represent "normal-hearing" responses in the auditory nerve to these stimuli. Additionally, NAPs are generated to represent the neural activity induced by cochlear implant stimulation strategies, assuming exponential rolloff from the electrodes. The mean squared error is measured between NAPs both directly, and after compensation for perceptual resolution. Results suggest that the noise-band approximation of the CIS implant signal actually has more in common with the original source than with the implant stimulation patterns.

Children with profound congenital or prelingual deafness encounter significant difficulties in the development of skills in an oral language such as English. Their language development, however, can be accelerated if they receive a cochlear implant-a sensory aid that facilitates language acquisition by providing important auditory information. The present study used the Reynell Developmental Language Scales (RDLS) to assess language skills pre- and postimplant in 44 pediatric cochlear implant users. All users were profoundly to totally deaf, either at birth or before the age of 3 years. They all received cochlear implants before the age of 6 and were programmed with state-of-the-art stimulation strategies (CIS or SPEAK) since the day of initial stimulation. The main finding was that postimplantation language development proceeded at a pace that was not significantly different from normal. Thus, the language gap present at implantation did not increase after children started using the device, as it would if they had not received cochlear implants. Nevertheless, it is important to conduct further studies to determine whether these conclusions apply when other language skills, such as the use of grammar, are measured

Cochlear implant (CI) users differ in their ability to perceive and recognize speech sounds. Two possible reasons for such individual differences may lie in their ability to discriminate formant frequencies or to adapt to the spectrally shifted information presented by cochlear implants, a basalward shift related to the implant's depth of insertion in the cochlea. In the present study, we examined these two alternatives using a method-of-adjustment (MOA) procedure with 330 synthetic vowel stimuli varying in F1 and F2 that were arranged in a two-dimensional grid. Subjects were asked to label the synthetic stimuli that matched ten monophthongal vowels in visually presented words. Subjects then provided goodness ratings for the stimuli they had chosen. The subjects' responses to all ten vowels were used to construct individual perceptual 'vowel spaces.' If CI users fail to adapt completely to the basalward spectral shift, then the formant frequencies of their vowel categories should be shifted lower in both F1 and F2. However, with one exception, no systematic shifts were observed in the vowel spaces of CI users. Instead, the vowel spaces differed from one another in the relative size of their vowel categories. The results suggest that differences in formant frequency discrimination may account for the individual differences in vowel perception observed in cochlear implant users

This paper considers the information transmitted in absolute judgments as encoded in a stimulus-response matrix (e.g., see Garner and Hake, 1951). When transmitted information is plotted against the number of stimulus categories in the matrix, one obtains a curve that increases monotonically toward a plateau, which is the maximum information transmittable per stimulus for the particular range of stimuli employed. We demonstrate that although the maximum information transmitted is an attribute of the stimulus continuum itself, the shape of the curve is an empirical property of the stimulus-response matrix, which is determined, in part, by maintaining a constant stimulus category width. Therefore, in principle, each curve of information transmitted vs number of stimulus categories can be determined by a single point: the rightmost point on the graph.

This study examined two possible reasons underlying longitudinal increases in vowel identification by cochlear implant users: improved labeling of vowel sounds and improved electrode discrimination. The Multidimensional Phoneme Identification (MPI) model was used to obtain ceiling estimates of vowel identification for each subject, given his/her electrode discrimination skills. Vowel identification scores were initially lower than the ceiling estimates, but they gradually approached them over the first few months post-implant. Taken together, the present results suggest that improved labeling is the main mechanism explaining post-implant increases in vowel identification