Contribution of auditory cortex to sound locahzation in the monkey ( iMaccicu mulntrn

THE ANALYSIS OF the two chief binaural cues for the direction of the source of a brief sound (A t and Aj) probably takes place in the superior olivary complex (cf. ref 2,6-8, 10, 12,2 1,22,24). Nevertheless, ablation of auditory cortex results in a dramatic and permanent disruption in the ability to localize sounds (15, 16, 20, 25). Since it is also known that auditory cortex ablation does not, in itself, abolish the ability to dis-criminate either At or A $ (1 l), thequestion arises: What is the basis of the cortical deficit? The idea that the cortical deficit may not be sensory in nature can be derived from Thompson and Welker (27), Beitel and Kaas ( l), and Ravizza and Masterton ( 19): either cats or opossums can indicate the di-rection of a sound source by a reflexive re-sponse even after bilateral ablation of au-ditory cortex. These results, when com-bined with the previous ones, show that au-ditory cortex ablation does not disrupt all of the responses to a localizable sound source but, instead, only some. Therefore, the stricly sensory capacity for sound localiza-tion itself may not depend on auditory cor-tex. The present report is the first in a series based on experiments exploring the be-havioral contributions of auditory cortex in the rhesus monkey (Macaca mulatta). In this report we present evidence that monkeys with lesions that include primary auditory cortex bilaterally can indicate the direction of the source of a click with a learned (i.e., nonreflexive) response, but they cannot lo-cate (i.e., move to) the source. This dissocia-tion of abilities shows that the deficit in sound localization that results from audi-Received for publication March 24, 1975. 1340 tory cortex ablation depends not on the sen-sory requirements of the task, but on the motor requirements; and therefore, it suggests that the role of auditory cortex in sound localization is probably not sensory nor perceptual but, rather, auditomotor or associative