Responses of single cells in cat inferior colliculus to binaural click stimuli: Combinations of intensity levels, time differences and intensity differences

Abstract

Click stimuli were used to study the responses of single units in the inferior colliculus to interaural time and intensity differences, using values for these differences that approximate those estimated to be produced by positioning of an actual source of sound. Effects of sound intensity level on interaural time and intensity responses were studied, as well as effects of binaural intensity difference on interaural time responses. Spike counts were plotted as a function of variation in interaural time or intensity. Four populations of neurons were described on the basis of these spike count functions; units sensitive to (1) interaural intensity differences, (2) interaural time differences, (3) neither interaural time nor intensity, or (4) both interaural time and intensity. With manipulation of intensity a unit may alter its properties so as to appear to shift from one of these populations to another. Four general types of interaural time sensitive functions and three general types of interaural intensity functions were described. It was proposed that complex types of unit interaural time codings suggest a convergence of lower order units, with simple codings, onto higher order complex units. Time-intensity trading was demonstrated by shifts of interaural time sensitivity functions along the time axis with binaural intensity manipulation. Other effects of both binaural intensity difference and intensity level were demonstrated. These results suggest dynamic and differential unit properties concerned with the representation of auditory space in the central nervous system.