Rats prepared with serial visual-cortical ablations can relearn the horizontal-vertical stripes discrimination problem if given interoperative training. However, they fail to discriminate between obliquely oriented stripes. The findings are discussed in relation to the concept that pattern perception is completely dependent upon the integrity of cortically related systems. Furthermore, the criteria for constructing pattern discriminanda are outlined, and reasons are presented for abandoning some of the classical stimuli used to test form perception in striate-extra-striate preparations.It is thoroughly established that if rats are given training on a black-white discrimination problem and then subjected to bilateral ablations of the posterior cortex, they show no postoperative retention of performance of the problem but can nonetheless relearn it. Lashley (1935) believed that relearning of the problem was a function of subcortical systems, and his concept has since been supported by Horel, Bettinger, Royce, and Meyer (1966) and Meyer, Yutzey, Dalby, and Meyer (1968). The latter studies have shown that the problem is relearnable by rats with complete neocortical ablations, regardless of whether the ablations are performed with one-stage or two-stage procedures.More recent research has been directed toward assessments of the variables which govern the rate at which the problem is relearned by rats with posterior ablations . One of the approaches has involved the use of procedures in which the animals are trained on the problem, subjected to unilateral posterior cortical ablations, then given inter operative retraining on the problem, SUbjected to second-stage ablations of the contralateral cortex, and then re-retrained on the problem. When this serial unilateral method is employed, the problem is finally relearned at a rate that is faster than the rate at which the problem is relearned by one-stage bilateral posterior preparations, or by subjects with two-stage posterior ablations which receive no interoperative practice

It has been established that if rats are prepared with perinatal injuries to the visual neocortex, are trained as adults on the black-white discrimination, and are then prepared with second-stage ablations of the rest of the neocortex, the effects of the second-stage injuries upon performance of the task are much more severe than those that are produced by extravisual injuries if the first-stage injuries to the visual neocortex are also inflicted in adulthood. This investigation presents a symmetrical result, that is, an enhancement of the deficits produced by injuries to the visual neocortex in adulthood by preexisting perinatal injuries to the extravisual cortex.Horel, Bettinger, Royce, and Meyer (1966) compared the effects of bilateral ablations of the anterior cortex upon the performances of rats that had learned a black-white discrimination problem while their brains were intact with those of rats that had learned the same problem after having been prepared with first-stage bilateral ablations of the posterior cortex. The findings were that even though the latter animals were tested for retention after second-stage injuries that completed the destruction of the cortex, the two groups of subjects relearned the problem at the same rate. Hence, it appeared that, insofar as performance of a simple visual habit is concerned, the cost of an injury to the extravisual cortex is completely independent of whether or not the visual neocortex is intact. Howarth, Meyer, and Meyer (1979) have recently confirmed the foregoing set of observations. But Howarth et al. also studied the effects of perinatal injuries to the posterior cortex upon the consequences for performance of the problem of anterior injuries in adulthood. They found that, for those conditions, second-stage bilateral ablations of the anterior cortex severely attenuate the rate at which the problem is relearned. Indeed, their best estimate was that the latter subjects required as many trials to relearn the problem as would have been expected if the rats had been prepared with one-stage bilateral ablations of the entire neocortex.In this investigation, we have asked the converse question, namely, whether perinatal anterior injuries will bring about a comparable enhancement of the This research was supported by Grant MH062 I I from the National Institute of Mental Health, and was conducted while the second, third, and fourth authors were Fellow in Developmental Psychobiology with support from Training Grant MH15677 from the National Institute of Mental Health.Copyright 1980 Psychonomic Society, Inc. 9role of systems related to the posterior cortex in performance of the black-white problem. It is thoroughly established that posterior subjects have greater impairments of performance of the problem than animals with anterior injuries, and also that the rate at which they relearn the problem is the same as the rate at which the problem is learned by naive posterior preparations (cf. Meyer & Meyer, 1977, for review). Moreover, Horel et al. (1966) have observed that...

Rats were first prepared with unilateral injuries to the posterior cerebral cortex. Then they were trained on the black-white discrimination problem. and afterwards were tested for performance of the problem after having been prepared with contralateral posterior injuries. The animals exhibited complete forgetting of the habit. The finding indicates that the protection of retention that is commonly observed in subjects that are trained between two successive posterior ablations is a function of their having a preoperative memory to recall. It also contradicts predictions from the theory of cortical suppression and the theory of state-dependency.It is thoroughly established that if normal rats are trained on a black-white discrimination problem, and are tested for postoperative performance of the problem after having been prepared with one-stage bilateral ablations of the visual neocortex, they exhibit an essentially complete forgetting of the problem but can nonetheless relearn it