Representation of vowel stimuli in the ventral cochlear nucleus of the chinchilla.

Responses of neurons in the ventral cochlear nucleus (VCN) of anesthetized chinchillas to six synthetic vowel sounds (/a/, /e/, /epsilon/, /i/, /o/ and /u/) were recorded at several intensity levels. Stimuli were synthesized with a fundamental frequency of 100 Hz or 181.6 Hz and had formant values at integer multiples of 100 Hz. Responses came from most neuron types in the VCN (with the exception of onset cells with an I-shaped pattern). Population studies, performed only on primary-like (PL) and chopper neurons, showed that PL neurons provide a better temporal representation than do chopper neurons. At the lowest level of stimulation, all neuron types provide an accurate rate-place representation of vowel spectra. With an increase in stimulus level, the rate-place representation of PL neurons becomes inferior to that of chopper neurons, either sustained choppers or transient choppers.