The ability of inferior colliculus neurons to signal differences in interaural delay

Sound localization in humans depends largely on interaural time delay (ITD) . The ability to discriminate differences in ITD is highly accurate. ITD di scrimination (Delta ITD) thresholds, under some circumstances, are as low a s 10-20 mus. It has been assumed that thresholds this low could only be obt ained if the outputs from many neurons were combined. Here we use Receiver Operating Characteristic analysis to compute neuronal Delta ITD thresholds from 53 cells in the inferior colliculus in guinea pigs. The Delta ITD thre sholds of single neurons range from several hundreds of mus down to 20-30 m us. The lowest single-cell thresholds are comparable to human thresholds de termined with similar stimuli. This finding suggests that the highly accura te sound localization of human observers is consistent with the resolution of single cells and need not reflect the combined activity of many neurons.