J. M. Warren

Selective sparing after lesions of visual cortex in newborn kittens

Previous findings are discordant regarding the effects of perinatal lesions of Cortical Areas 17 and 18 on visual discrimination learning in cats. Three potential determinants of such sparing were investigated: age at lesion (4 or 181 days), age at testing (3 or 9 months), and stimulus complexity. Age at testing was not significant, but performance varied with stimulus complexity and cortical damage, and there was an interaction between stimulus complexity and age at lesion. Both operated groups were transiently impaired in discriminating objects and subsequently learned to discriminate simple 2-dimensional patterns as well as done by controls, but the lesion groups were permanently impaired in discriminating similar patterns circumscribed by irrelevant lines. The age-at-lesion groups differed, however, in discriminating patterns masked by superimposed lines. The group lesioned at 181 days was severely impaired at both acquisition and subsequent intercurrent performance; the group lesioned at 4 days was impaired only at intercurrent performance. This study suggests that sparing after early postnatal damage of Areas 17 and 18 occurs only under limited circumstances.

Delayed response learning by cage-reared normal and prefrontal cats

Twelve intact cats and eight with lesions in the prefrontal cortex were trained on two-choice locomotor delayed response with auditory cues. The groups did not differ significantly on predelay, 0-, and 5-sec delays; eight controls, but no frontals, met criterion on 15-sec delays (p =.01). Prefrontal lesions impair the learning of delayed response but not as severely as is the case with adult rhesus monkeys. The cage-reared normal cats learned delayed response more slowly than Divac’s (1968) trapped alley cats tested under almost identical conditions, confirming previous observations that cage-rearing interferes with some spatial learning capacities in cats.

Delayed response performance by rhesus monkeys with midprincipalis lesions

Four rhesus monkeys were trained on delayed response in the WGTA and subjected to lesions of the middle third of sulcus principalis. Two monkeys were very severely impaired in postoperative retention tests; two Ss manifested milder deficits in postoperative performance. It was concluded that the middle third of sulcus principalis is important for the mediation of delayed response as well as delayed alternation and that the two tasks probably are equivalent measures of the same supramodal learning process.

Perimeter, complexity and generalization of a form discrimination by cats

Sixteen cats learned a successive discrimination between circles and 1-shaped figures and were then tested for generalization with seven new stimulus figures. Seven cats maintained responsiveness to visual cues on the generalization tests, and the results from these Ss indicated that cats classify visual figures as open or closed in terms of both complexity (number of sides) and perimeter. The other nine cats continued to respond correctly to the training figures but manifested strong position preferences on the nondifferentially rewarded test trials. The results are compatible with the argument that stimulus generalization reflects a failure of discrimination.

Spatial probability learning by cats

Groups of six cats were trained, with noncorrection or with guidance, for 1200 trials on each of four ratios of reinforcement: 70:30, 60:40, 40:60 and 30:70, in a spatial probability learning experiment. Both groups eventually learned to choose the more frequently rewarded stimulus on almost every trial, the noncorrection Ss learning to do so much sooner than the guidance Ss. The results of this experiment with cats tend to agree with previous observations that rats and monkeys maximize on spatial probability problems. The available evidence, however, indicates that cats tested with guidance on spatial probability problems learn to maximize considerably more slowly than rhesus monkeys and that monkeys are, in turn, inferior to rats.

Performance of immature and adult cats on the Hamilton search test

Nine groups of cats differing in age, breed, past experience on learning tasks, and neurological status were tested on Hamilton’s multiple choice test. No significant intergroup differences were obtained, suggesting that the Hamilton search test is of little or no value for investigating either the ontogeny or phylogeny of learning. The finding that normal cats and cats with lesions in the frontal association cortex do not differ in the efficiency of their searching behavior confirms results previously obtained from monkeys.

Overtraining, extinction, and reversal learning by kittens

Two groups of kittens received 0 or 112 overtraining trials after learning a brightness discrimination. Both groups underwent extinction of differential choice responses and then learned the reversed brightness discrimination. The overtrained and nonovertrained animals did not differ significantly in rate of reversal learning, and both groups showed a significant preference for the old positive stimulus when differential reinforcement was reinstated in reversal training. According to Sutherland and Mackintosh, these results show that kittens lack stable attention and should be inept in dealing with reversal and probability problems. This is not the case, raising doubts about the adequacy of their account of interspecies differences in learning by vertebrates.

Generalization of responses to intermediate size by cats and monkeys

After learning to choose the middle sized of three squares, 16 cats and 14 rhesus monkeys manifested much less generalization of response on 10 equivalence tests than 16 control cats trained to select the smallest or the largest of three stimuli. These results are more compatible with Spence’s theory of transposition than with relational theories of transposition.

Irrelevant cues and shape discrimination learning by cats

Experimentally naive eats learned to discriminate a pair of objects (circle and triangle) that differed in external contour, with no irrelevant cues (N = 30), with irrelevant brightness cues (N = 26), and with irrelevant size and brightness cues (N = 26). In a second experiment, naive cats were trained to discriminate bidimensional patterns (circle and triangle) with no irrelevant visual cues (N = 24) or with irrelevant size and brightness cues (N = 26). Irrelevant cues did not significantly affect the rate of shape discrimination learning in either experiment. The findings disagree with the results of several similar experiments with rats.

Pretraining and discrimination reversal learning by rhesus monkeys

Groups of five to seven macaques were trained on repeated reversals of a visual (or spatial) discrimination habit after no pretraining, extended discrimination training, or repeated reversal training on spatial (or visual) cues. Neither sort of pretraining had a significant effect on reversal learning on the second cue. These results indicate that monkeys’ capacity to develop generalized “win-stay, lose-shift” hypotheses may have been exaggerated in previous experiments.