Role of brainstem auditory structures in sound localization. I. Trapezoid body, superior olive, and lateral lemniscus.

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Abstract
Cats were trained to perform 2 discriminations of lateralized sound images. In the 1st of the 2 tasks the cats were trained to respond when a train of clicks to the left ear was replaced by a train of clicks to the right ear. In the other task a train of click pairs, one click of a pair to each ear, was substituted for the single clicks. The task required the discrimination of click pairs in the order left-right from pairs in the order right-left. Testing on this task was continued while the threshold interaural time difference was estimated. In cats with intact auditory systems both tasks are quickly learned, training on one task transfers to the 2nd and the interaural time threshold averages less than 50 Msec. After complete trapezoid body section the threshold is elevated to 500 Msec which is a total loss of capacity to discriminate time disparities in the range that occurs in natural sound localization. With only partial section of the trapezoid body, elevations in threshold are related to the extent of the lesion. Cats with lesions in the lateral lemniscus have no difficulty in learning the discriminations and show no clear change in time disparity threshold; but they fail to transfer training on the first discrimination to the second discrimination.