Fig. 8. Discrimination of figures that contain more than one element. (A) Fish A could be trained to discriminate a pattern card with only one centrally placed black disk (rewarded, ‘+’) from a card with two equally sized disks (unrewarded, ‘–’). The numbers of choices of the two pattern cards in 100 unrewarded tests are given below the patterns. In transfer tests in which the single disk was larger in size or placed off-centre, the fish still preferred the card with a single disk. (B) The results of these transfer tests conform with a template-matching mechanism in which the fish (i) treated the double figure as one figure that is laid on the template such that the centres coincide and (ii) quantified the match by the relative overlap L/(L+T+M). The values of L, T and M, to assess the quality of the match (see Fig. 4), are given for both test pairs. Disk diameters are indicated. For definitions of L, M and T, see Fig. 4. A, area of stored template.
