Fig. 3. Visual pattern discrimination and transfer tests in Gnathonemus petersii. Fish A–C could be successfully trained to discriminate the patterns shown in the top row. In each case, approach towards the disk was rewarded (indicated by ‘+’). To analyze the variables used by the fish to discriminate these patterns, a series of unrewarded transfer tests was conducted (Testing). In these, fish were tested with patterns that differed from the training patterns. These presentations were interspersed with rewarded presentations of the training patterns (at a ratio of approximately 1:3). For each fish, the patterns used in the transfer tests are shown below the respective training patterns, and the absolute numbers of choices are given below each pattern. The scale bar indicates 10° of visual angle.
