Rats were subjected to visual-cortex damage either at 1 day of age or in adulthood and their ability to utilize pattern cues was assessed. No age effect was obtained. This was true for Ss with all or part of visual cortex removed and for Ss maintained postoperatively in visually rich, poor, or ordinary lab environments. The study did demonstrate, however, that Ss with visualcortex damage tend to use luminous flux cues while normal SB tend to use pattern cues in performing a brightness discrimination task, and further, that performance of the brightness discrimination task by Ss subjected to tissue removal can be affected by lesion size. EXPERIMENT 1The primary purpose of this study was to determine whether early visual-cortex damage is visually less incapacitating than later damage. Some suggestive evidence for this possibility can be found from work on the rat (Tsang, 1937) and on the cat (Doty, 1961; Wetzel, Thompson, Horel, & Meyer, 1965). In Experiment 1 the pattern vision of rats operated at 1 day or 3 mo. of age was assessed after equal postoperative recovery periods. These Ss as well as control Ss were first trained to perform an 8:1 light discrimination and then given transfer tests designed to determine whether the animals were using pattern or luminous flux cues in learning the discrimination. In addition, Ss were trained on a horizontal vs. vertical stripes pattern discrimination. MethodSubjects. The 14 male and 13 female Long-Evans black-hooded rats were divided into four groups; a neonatal visual-cortex ablation group (NL, n -6); a neonatal operated-control group (NC, n = 7); a 3-mo.-old visual-cortex ablation group (AL, n -7); and a 3-mo.-old normal-con-

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Unilateral subtotal collicular and, large but not small, unilateral posterior cortical lesions in rats produced ipsiversive progression tendencies in a visual task. However, no support could be given to the view that the progression tendencies following unilateral collicular lesions are in part a reflection of contralateral visuosensory-field deficits. Thus, performance of a light-dark task was equally good when vision was restricted to the eye leading to the damaged colliculus as when restricted to the eye leading to the undamaged collicullus. la addition, bilateral collicular lesions had no effect on performance of either the light-dark or a stripes discrimination task. The study indicated the need for caution in basing interpretations of the nature of vision on simple response tendencies.