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Winter, Ian M.; Palmer, Alan R.; Wiegrebe, Lutz ORCID: 0000-0002-9289-6187; Patterson, Roy D. (2003): Temporal coding of the pitch of complex sounds by presumed multipolar cells in the ventral cochlear nucleus. In: Speech Communication, Vol. 41, No. 1: pp. 135-149
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Extensive studies of the encoding of fundamental frequency (f(0)) in the auditory nerve indicate that f(0) can be represented by either the timing of the neuronal discharges or the mean discharge rate as a function of characteristic frequency. It is therefore of considerable interest to examine what happens to this information at the next level of the auditory pathway, the cochlear nucleus. Both physiologically and anatomically the cochlear nucleus is considerably more heterogenous than the auditory nerve. There are two main cell types in the ventral division of the cochlear nucleus;bushy and multipolar. Bushy cells give rise to primary-like responses whereas multipolar cells may be characterised by either onset or chopper type responses. Physiological studies have suggested that onset and chopper units may be good at representing the f(0) of complex sounds in their temporal discharge properties. However, in these studies the pitch-producing sounds were usually characterised by highly modulated envelopes and it was not possible to tell if the units were simply responding to the modulation or the temporal fine structure. In this paper we examine the ability of onset and chopper units to encode the f(0) of complex sounds when the modulation cue has been greatly reduced. These stimuli were steady-state vowels in the presence of background noise, and iterated rippled noise (IRN). The response of onset units to the vowel f(0) in the presence of background noise was varied but many still maintained a strong response. In contrast, the majority of chopper units showed a greater reduction in their response to vowel f(0) in the presence of background noise. In keeping with the vowel study, the responses of both types of unit to the delay of the IRN was reduced in comparison with their response to more highly modulated stimuli. Increasing anatomical, pharmacological and physiological evidence would seem to argue against onset units playing a direct role in pitch perception. However, some units, identified as sustained choppers, may be able to represent the pitch of complex sounds in their temporal discharges. (C) 2002 Elsevier Science B.V. All rights reserved.