Effect of auditory neocortex ablation on pitch perception in the cat

Cats which received one- or two-stage bilateral ablations of auditory cortex were compared to unoperated cats on a test involving the discrimination of increases (1.2 kHz) from decreases (0.8 kHZ) in the frequency of ongoing 1.0-kHz tone pulses. Whereas two-stage cats exhibited more evidence of postoperative retention for the original task than did one-stage cats, both groups relearned the discrimination in approximately the same number of trials as normal cats. Individual differences in difficulty of relearning apparently reflected the degree of undercutting of the polysensory association areas of the suprasylvian and lateral gyri. Following retraining, all cats received two discrimination transfer tests. The first test was identical to the original dis crimination problem in all respects except that different frequency values were substituted for the original set (i.e., 1.6-kHz tones alternating with either 2.0- or 1.2-kHz signals). Whereas both unoperated and two-stage cats had difficulty discriminating the new positive from negative trials, the one-stage cats exhibited a significant tendency to continue responding to changes invoving 1.2-kHz tones in the same manner as in the original discrimination task. In the second test the cats were asked to discriminate the original 1.2- and 0.8-kHz tones against a silent background. Both operated and unoperated cats performed significantly above chance on this test. These results suggest that the cats solved the original discrimination on the basis of absolute frequency cues rather than the directionality of frequency changes. The significance of these findings are discussed in relation to current concepts of the functional capacity of auditory decorticate animals.