AbstractIn a previous experiment on the visual discrimination of open and closed shapes by rats (Sutherland, Carr, and Mackintosh, 1962) it was found that (1) at the beginning of training the animals exhibited a strong preference for the more open shape; (2) shapes differing in their horizontal projections only were more discriminable than shapes differing in their vertical projections only. The present experiment is a replication of the earlier one using different shapes and different apparatus. The first result was fully confirmed and some confirmation was obtained for the second, although late in training the differences between groups trained with shapes differing on opposite projections were not statistically significant.