ABSTRACT
Neurons in the cochlear nerve and ventral cochlear nucleus encode within their temporal firing patterns the periodicity of low-frequency (< 4 kHz) complex tones. Cochlear nerve fibers synchronize their discharge activity to a cochlear-filtered, half-wave-rectified (CFHWR) version of the signal’s temporal-fine-structure. As a consequence, information relevant to the signal’s low pitch is manifest in the autocorrelation of the unit’s timing pattern when synchronized to a CFHWR reflecting the interaction of two or more contiguous spectral components. At the level of the ventral cochlear nucleus there occurs a diversification of cellular response patterns with respect to encoding waveform periodicity. Three physiological response classes may be distinguished: (1) “Primary-like” units (concentrated in the anteroventral cochlear nucleus) respond in a manner analogous to cochlear nerve fibers of comparable characteristic frequency and spontaneous rate. (2) “Chopper” units generally synchronize to the envelope of the CFHWR waveform, provided the signal’s modulation frequency lies within the temporal bandpass characteristic of the neuron. (3) “Onset” neurons, under appropriate signal conditions, synchronize to the input signal’s pitch period. Thus, at this relatively peripheral level of the auditory pathway, there occurs a functional diversification of physiological response patterns of potential relevance for encoding three distinct features of signal periodicity.
