Vowel discrimination using different frequency-to-electrode maps in cochlear implant users

• Published in: The Journal of the Acoustical Society of America Vol. 82; no. S1; p. S71
• Main Authors: Svirsky, Mario A., Cullen, John K., Ragland, Howard P., Walker, Cedric F.
• Format: Journal Article
• Language: English
• Published: 01-11-1987
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.2024953

The Nucleus WSP-III is a speech processor for cochlear implants that stimulates two electrodes per fundamental period. The electrodes stimulated are chosen based on the first two formant frequencies: lower frequency formants excite electrodes that are more apical. This gives users a cue to discriminate vowels with different formants. But, if two particular vowels had second formants close enough to fall within the frequency band of some electrode, the user would miss that cue—those two vowels would “behave” as if they had exactly the same second formant. Cochlear implant users were tested under three frequency-to-electrode maps: the standard map (used by most Nucleus implant patients), the modified standard map (proposed by P. Blamey, private communication, 1987) and a new map designed to maximize contrast between different vowels. A discrimination test was used where subjects were not asked to identify the sounds they heard, but only to indicate whether the different word in a set of three was in the initial or final position. This tends to minimize learning effects due to prior experience with a given map. Also, if cochlear implant users can discriminate different phonemes, they could conceivably be trained to identify them correctly, whereas lack of discrimination makes identification impossible. [Work supported by Cochlear Corp. and Sigma Xi.]