Sensitivity to interaural temporal disparities of low- and high-frequency neurons in the superior olivary complex. II. Coincidence detection.

In the companion paper we demonstrated that neurons in the superior olivary complex that were sensitive to interaural temporal disparities (ITDs) could be divided into two broad categories: peak type and trough type. Within these broad categories, many neurons exhibited various types of irregularities in their responses. In the present paper we devise three criteria to determine whether all types of neurons act as coincidence detectors. Each criterion relies on a comparison between the synchrony of the responses to the wave-forms at either ear and the "interaural synchrony," i.e., the response to a cyclically varying ITD. First, a neuron should exhibit synchrony to both the ipsilateral and contralateral waveforms over the entire range, to which it is sensitive to ITDs. Second, the ITD that elicits maximal discharge should be equal to the delay required to bring the ipsilateral and contralateral waveforms into coincidence. Third, the strength of interaural synchrony should be predicted by the strengths of synchrony to the waveforms at either ear. We found that most neurons of all types in the superior olivary complex met these criteria. Thus coincidence detection is a basic operating principle for all forms of ITD sensitivity.