Fig. 6. Attempts to falsify the template-matching hypothesis. Fish B and C were both trained to discriminate a disk (rewarded figure, ‘+’) from an upright triangle (‘Training’). After unrewarded tests with the training patterns revealed that both fish had learned the task (‘Testing’; absolute numbers of choices by fish B are given below the respective patterns with the absolute numbers of choices by fish C in parentheses), transfer tests were conducted in which size-reduced versions of the disk and the triangle were shown that should be indistinguishable to a template-matching system. In these tests, both fish chose randomly (numbers of choices given below figures). To analyze whether the loss of preference for the disk was because the size-reduced test patterns were too small to be discriminated, both fish were subsequently trained to discriminate the test patterns, and both successfully learned this discrimination. The sizes of the respective patterns (diameter of disk and side length of triangle) are indicated.