ASA 125th Meeting Ottawa 1993 May

2aPP4. Neurophysiological correlates of the pitch of complex tones.

Bertrand Delgutte

Eaton--Peabody Lab., Mass. Eye & Ear Infirm., Boston, MA 02114

, Res. Lab. of Electron., MIT

, and Harvard--MIT Div. of Health Sci. & Technol.

Peter A. Cariani

Mass. Eye & Ear Infirm., Boston, MA

, and Harvard--MIT Div. of Health Sci. & Technol.

Mark J. Tramo

Mass. Eye & Ear Infirm., Boston, MA

, and Harvard Med. School

The pitch of complex tones plays an important role not only in speech and music, but also for perceptual segregation of sound sources. In order to study physiological correlates of these phenomena, autocorrelation histograms were recorded and computed from auditory-nerve fibers in anesthetized cats to estimate the aggregate interspike interval distribution for the entire auditory nerve. Results for many types of complex stimuli (including those used in classical pitch shift and pitch dominance experiments) suggest that the perceived pitch corresponds to the most frequent interspike interval in the auditory nerve. Also investigated was how interspike interval information might be used to separate simultaneously presented vowels. Psychophysical experiments show that both constituents in a pair of concurrent vowels are better identified when they have slight different pitches. These results show that concurrent vowels can usually be segregated from the information in the aggregate interspike interval distribution, and that peformance improves when the vowels have different pitches even though the method used does not rely on explicit pitch identification. [Work supported by NIH Grant Nos. DC00119 and DC00038.]