Effects of ablations of temporal cortex upon speech sound discrimination in the monkey.

Ten monkeys were trained on two auditory discrimination problems of different levels of difficulty plus one visual pattern discrimination task. Bilateral cortical ablations were made of either the ventral portion of the superior temporal gyrus to the depth of the superior temporal sulcus in the midtemporal region, or of the primary auditory projection cortex of the supratemporal plane extending onto the insular cortex in the depths of the lateral fissure. Monkeys with bilateral ablations of inferior temporal cortex were included as controls. Post operative performance revealed a modality-specific deficit in audition for the midtemporal area, and an apparent inability to relearn a speech-sound discrimination after lesion of primary auditory cortex.