Auditory-visual associations, hemispheric specialization and temporal-frontal interaction in the rhesus monkey.

Monkeys (Macaca mulatta) learned preoperatively to associate each of 6 auditory stimuli with 1 of 6 visual stimuli. Ablation of the left prefrontal cortex in a group of 3 monkeys produced a substantial impairment in performance of the task, though performance was still above chance. Ablation of the right prefrontal cortex in a second group of 3 monkeys was without effect. Subsequently the superior temporal gyrus (auditory cortex) was removed in each animal unilaterally in the hemisphere contralateral to the existing prefrontal ablation. Ablation of the left auditory cortex produced a severe impairment, but ablation of the right auditory cortex was without effect. Finally, forebrain commissurotomy in the animals with left prefrontal and right temporal ablation reduced their performance virtually to chance level. These results are consistent with previous findings indicating a left hemisphere specialization for audition in the monkey, and they give strong support to the idea, derived from previous experiments on difficult associative learning in the monkey, that auditory-visual association depends on a convergence of auditory and visual information in the prefrontal cortex.