Cochlear Nerve and Cochlear Nucleus Responses to the Fundamental Frequency of Voiced Speech Sounds and Harmonic Complex Tones

The responses of many types of unit in the cochlear nucleus to complex sounds such as speech are strongly modulated at the period of the fundamental frequency (F0) of the sound. We have investigated the “pitch period following response” of cochlear-nucleus onset units using harmonic series and speech sounds. Responses to harmonic complex tones with components all with cosine starting phase were modulated at the F0, whereas alternating phase harmonic series resulted in modulation at twice the F0. These results suggested that the onset units were simply amplifying the modulation present in the discharge of auditory nerve fibres. Background noise severely degrades the modulation present in auditory nerve fibres of high characteristic frequency (CF). However, many onset units with similar CF showed strong F0 modulation under these conditions. Thus a simple following of modulation in cochlear nerve fibres at the same CF is insufficient to explain onset cell responses.