Categorical color coding in goldfish

Goldfish, trained in the shuttlebox apparatus to avoid shock, acquired a color discrimination between two colors (red/green) and were tested in transfer with a new set of colors (yellow/blue). Transfer color shock-pairing was either consistent with (red=yellow, blue=green) or opposite to (red≠ yellow, green≠blue) categorical color coding seen in pigeons. Groups with transfer shock-pairing consistent with categorical color coding showed positive transfer, and groups with transfer shock-pairing opposite to categorical color coding showed negative transfer, similar to an attenuated reversal learning effect. These results indicate that goldfish, like pigeons, code different colors as behavioral equivalents even though they can easily learn to discriminate between them. As with pigeons, the finding of the categorical color coding phenomenon changes the conclusions drawn from earlier goldfish conditional-discrimination transfer studies using only signal color changes between acquisition and transfer testing, from evidence of concept learning to evidence for categorical color coding, on the grounds of parsimony. It is important to note that this finding affects only the explanation of conditional-discrimination transfer effects, and the fact remains that both pigeons and goldfish can learn to conditionally discriminate—pigeons for positive reinforcement, and goldfish to avoid shock.