The influenee oflesions located generaIly within four regions of the rat's posterior neocortex upon the aequisition and retention of two-choiee visual discriminations was assessed using a Thompson-Bryant apparatus. The ability to distinguish visual patterns was tested by utilizing stimuli eomposed of 45° versus 135 0 alternating blaek and white stripes (both total and local luminanee eues were eontroIled). "Brightness" discrimination was assessed by using blaek and white eard discriminanda. Posterior parietal injuries resulted in a dysfunction on eaeh of the four tasks, but rats with this injury eventuaIly attained eriterion for eaeh ofthe habits. SmaIler, more anteromedial parietallesions failed to disturb pattern discrimination and were not studied in the other paradigms. The only defieit observed in rats with medial peristriate injuries was a slight retardation in aequisition of the pattern discrimination. Sinee the effects of lateral peristriate and striate injuries upon pattern vision have been weIl described previously, the effects of these lesions on the retention and aequisition of the blaek-white discrimination were studied. Lateral peristriate lesions, but not striate lesions, were associated with a retention loBS of the brightness problem. This loss was detected even with a recovery interval of 60 days. Both striate and lateral peristriate lesions retarded blaek-white discrimination aequisition. Discussion foeuses on the probable natures of the visual dysfunctions associated with these injuries.Ablation of the rat's posterior neocortex has been reported to produce an abolition of form vision (e.g.,
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