Reversal set formation in the visually decorticate rat.

Abstract

Rats given large visual cortex lesions demonstrated a simultaneous task reversal deficit previously reported to follow more extensive cortical ablation. However, no deficit appeared in an operant discrimination that deemphasized visuospatial cues, and the simultaneous task deficit vanished when translucent eye occluders were applied to eliminate spatial, but not intensity, cue use. Because the lesion subjects showed an impairment only when visuospatial cues were available and relevant to correct reversal performance, they seemed hindered by their incompetent processing of visuospatial information. The results are interpreted as support for spatial rather than learning approaches to visual cortex function.

Effect of posterior cortical lesion on two versions of the brightness-discrimination task

“…Results of the present investigation failed to extend the generality of the Birch et al (1978) contention that the postoperative behavioral deficits of striate-Iesioned rats are based on an inability to integrate spatial and luminous flux cues. That view has suggested that so long as only luminous flux and not spatial cues are present, lesioned animals show little or no discrimination deficit.…”

“…Despite the apparent lack of support for the view that reduced spatial task components yield reduced impairment on a brightness discrimination, the results of Experiment 1 seemed open to the criticism that the present test technique (acquisition/retention) was different from the one in which Birch et al (1978) found spatial-cue reduction to be effective in improving performance (successive discrimination reversal, SDR). Experiment 2 attempted to evaluate potential differences associated with these two methods of measuring brightness discrimination.…”

“…However, the present provision of an open-field task designed to reduce the spatial characteristics relative to the usual twoalternative directional maze still yielded impairments at least the equivalent of those seen in a Y -maze with matched discriminative properties. Because the Birch et al (1978) result had been demonstrated in a test situation in which successive reversals of a brightness task served as the dependent measure, this test procedure was applied in Experiment 2 of the present investigation. Here, too, spatial-cue reduction of the type provided by the open field did not yield any reduction in severity of the lesionbased behavioral deficit, and contrasting outcomes did not seem attributable to inherent differences between successive reversal and simple acquisition measures.…”

“…In contrast to memorial interpretations of the lesionbased deficit, Cooper and his co-workers have suggested that an inability to combine visual and spatial components of the criterion task underlies the behavioral deficit associated with posterior decortication. Empirical support for this hypothesis has been provided by Birch, Ferrier, and Cooper (1978), who compared the normal rat's improvement over the course of successive reversals with that of operated animals and noted a significant lesionbased deficit. However, when operated subjects wore translucent, light-diffusing occluders over their eyes, the typical impairment was ameliorated and improvement over successive reversals was observed.…”

Posterior cortical lesion influences on successive discrimination reversal performance by rats

“…Because the damaged areas in this study were more extensive than .the usual "visual" lesion and were inflicted at early ages, the basis of the impairment was not entirely clear. Accordingly, Birch, Ferrier, and Cooper (1978) undertook a replication of this study; they used adult animals and restricted removals to areas 17, 18, and 18a. Their results showed that failure to improve on successive reversals of a simultaneous brightness discrimination was a characteristic associated with the typical posterior-visual lesion so long as the task involved spatial properties, that is, so long as the rat was required to go to different locations to make choices of discriminanda.…”