Figure 2.

Test stimuli and experimental set-up. Three fish were trained to discriminate the reward colour from the other test colours. Test stimuli were designed so that they became progressively more similar to the reward. Two sets of colours were designed to test the fish in different parts of its perceptual colour space, the T series and the S series. (a) Test set-up, fish had to poke at the ‘poking’ spot below the stimulus to make a choice for a given stimulus. (b) Test colours in a Maxwell triangle showing their relative positions in colour space. (c) Close-up of colours in Maxwell triangle.