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Cats were trained to discriminate either between a horizontal and vertical rectangle or between two oblique rectangles, one at 45 degrees , the other at 135 degrees to horizontal. All animals were first trained with both shapes (one in each orientation) presented together, and then retrained with only one shape shown at a time. Throughout the experiment the animals being trained with oblique rectangles performed as well as those being trained with horizontal and vertical rectangles. This finding is in marked contrast with results obtained from other species. The results suggest that the ability of a species to discriminate between rectangles in different orientations may depend upon the relative numbers of cells in the visual system having receptive fields in each orientation.

1. Rats were maintained on a diet deficient in fat and on a normal diet of rat cubes. 2. Rats were trained to discriminate between vertical and horizontal striations. The minimal stripe width that could be used for discrimination was determined. 3. In bright illumination (0.7 or 4.5 ft.lamberts) both deficient and normal rats had the same ability to discriminate between black and white stripes. 4. With an illuminance of 0.002 ft.lambert, supplemented rats could discriminate as efficiently as at 0.7 ft.lambert, but deficient animals were unable to discriminate at 0.002 ft.lambert. 5. Control rats had 14% of docosahexaenoic acid in their retinal fats but the deficient rats had only 1%. 6. Deficient animals had no vitamin A stores in the liver whereas the control animals had about 190 i.u./g. 7. The visual acuity of the rats used was about 45' of arc.