ASA 124th Meeting New Orleans 1992 October

4pPPa3. Neuronal processing in cochlear nucleus of vowel combinations: Effect of intensity and intervowel time.

Pitchaiah Mandava

Allen L. Rupert

George Moushegian

Callier Center-UTD, 1966 Inwood Rd., Dallas, TX 75235

This study presents evidence on how three cochlear nucleus (CN) neuronal types, primary, chopper, and pauser/buildup, process complex sounds. The stimuli were vowels, /i/, /a/, and /u/, from three corners of the F1--F2 vowel space. Having first gathered neuronal data to vowels presented separately, pairs of these vowels were then delivered with intervowel time intervals from 0 to 100 ms in 20-ms steps. The intensities of both vowels were systematically varied. Vowel sound combinations almost invariably provoked changes in neuronal responsiveness, e.g., discharge rates and interval distributions. In some instances, a given vowel sound altered the discharge pattern to a succeeding one, even after time intervals extending to 60--100 ms. In others, the effect was maximal when the vowels had no time separation, and did not persist beyond 20 ms. Finally, various combinations in vowel intensities and intervowel times modified the temporal response characteristics of each neuronal type; but in particular the choppers, for which alterations were considerable.