Responses of the cat's collicular auditory neuron to human speech.

Collicular auditory neurons in cats were exposed to human speech sounds, and responses to the vowel /a/ in isolation and in connected speech were compared. The fundamental frequency coded was found to be independent of CF, response type ("on" type or slowly adapting), and directional sensitivity to frequency change. This suggests that the coding of speech sounds depends on the periodicity of the neural-response pattern. Responsiveness was generally greater to segmented vowels; it seems probable that a neuron's response adapts to and is suppressed by preceeding speech stimuli. The context in which a message is embedded may be very important for the processing of speech sounds.