Trevor M. Shackleton
Dept. of Exp. Psychol., Univ. of Sussex, Brighton, E. Sussex BN1 9QG, UK
Binaural processing of interaural time differences (ITDs) is widely believed to be performed by a cross-correlation mechanism. Cells have been found in the medial-superior olive (MSO) and inferior colliculus which respond most strongly when presented with stimuli with a characteristic ITD (EE cells). These cells are believed to form the basis for such a mechanism. In this study we compare the performance of cells based on simple cross-correlation, coincidence detector cells based on a novel deterministic method, and coincidence detectors based on Monte-Carlo simulation. The deterministic model is based upon the requirement that the probability of a given number of inputs from the auditory nerves of either ear must exceed a threshold amount within a finite time (coincidence window) before the modeled cell can fire. We examine the firing rate and vector strength as a function of ITD, overall level, and interaural level difference (ILD) and compare our results with the data from cells in the MSO. We find that a simple cross-correlation cell is inadequate to describe the data. However, the deterministic cell and Monte-Carlo simulation, both with a coincidence window width of 0.2 ms, describe the data very well. [Work supported by The Wellcome Trust, UK.]