Shigeya Yaginuma

Acquisition of discrimination learning of patterns identical in configuration in macaques (Macaca mulatta and M. fuscata).

The acquisition of discrimination of five pairs of pattern cues in a Wisconsin General Testing Apparatus by 223 naive macaque monkeys was compared. The pairs of discriminanda were identical in configuration but varied slightly in either the size of the cue or the size of the background plaque; thus, the degree of separation of the cue from the fringe of the plaque, the response site, was slightly different for each pair of discriminanda. These small differences in cue-response separation had marked effects on the rate of acquisition of the discriminations. Even an increment of separation as small as 0.5 cm resulted in a remarkable retardation of the acquisition. This retardation was due entirely to prolonged performance at the chance level, and not to a slow rate of improvement from the chance to a criterion level. The finding indicates that the difficulty in the acquisition learning on pattern tasks depends largely on the difficulty of attending to the pattern cues at small cue-response separations.

Further evidence on elevated discrimination limens for reduced patterns in monkeys with inferotemporal lesions

An attempt was made to elucidate the nature and neural basis of the elevated discrimination limen for visual stimuli of reduced sizes that had been discovered earlier in monkeys with inferotemporal lesions. Although anterior inferotemporal damage was found to have only negligible effect, both total inferotemporal and posterior inferotemporal lesions yielded markedly elevated limens for reduced pattern stimuli but not for reduced colour stimuli. The impaired animals could be trained to discriminate reduced patterns that were below their original discrimination limen, but this required many more trials than were needed for postoperative relearning of the initial pair; normal animals, by contrast, showed perfect transfer from the standard to the smallest pair. The findings suggest that the increased threshold for reduced patterns in monkeys with inferotemporal lesion is attributable not to a visual acuity disorder but to an impairment of pattern perception resulting mainly from damage to posterior inferotemporal cortex.

Effect of small cue-response separation on pattern discrimination in macaques (Macaca fuscata and M. mulatta).

In order to elucidate the nature of the effect of small cue-response separations on pattern discriminations by monkeys, three studies were performed. When training on a pattern discrimination with a cue-response separation was discontinued during performance at the chance level, there was no saving on the rate of learning a second task (with identical cues but a different cue-response separation) relative to the performance of naive control animals. By contrast, when training was discontinued at a performance level a little better than chance, there was significant saving on learning a second task. After learning the second task, a third task with new pattern cues was learned, with marked saving on the duration of performance at the chance level. The results indicate that during the initial stage of performance at the chance level, monkeys do not attend to cues if there is even a small separation between the cue and the response site.

2218 Effects of subdivisional inferotemporal lesions on visual habit formation and pattern perception in monkeys

Shigeya Yaginuma, Yasutaka Osawa, Kiyoko Yamaguchi Monkeys with lesions of the anterior and posterior halves of area TE (the TEa and TEp lesions, N=4 and 3, respectively) and area TEO (the TEO lesion, N=4) were tested on a discrimination limen task for patterns of reduced sizes, which has been thought to be a test of pattern perception. Another three monkeys served as the normal controls. The TEO group showed marked elevation of discrimination limen, whereas the TEa and TEp groups showed no or only slight elevation of discrimination limen. All animals had previously been tested on pattern discrimination learning tasks, which have been thought to be tests of visual habit formation as well as of pattern perception. On these tasks, the TEp and TEO groups showed the same degree of deficits, whereas the TEa group performed as well as normal controls. These patterns of impairment suggest that areas TEp and TEO are more closely involved in visual habit formation and pattern perception, respectively.