Visual contrast and color in rapid learning of novel patterns by chicks

Abstract

Biological communication signals often combine bright and dark colors, such as yellow and black, but it is unclear why such patterns are effective. The literature on aposematism suggests that high contrast patterns may be easily learnt or innately avoided, whereas studies of sexual signaling refer to their attractiveness or to their cost. Here, in experiments with poultry chicks trained to find food in patterned containers, we confirm that elevated contrast dramatically increases the rate of initial attack on novel stimuli, but this response is labile. The chicks pecked once at a novel unrewarded stimulus and then ignored it for at least 24 h. Such single trial learning has not previously been reported for birds without a positively aversive unconditioned stimulus such as quinine. We then tested and rejected two hypotheses about the function of high contrast patterns: first that the preferential responses are due to novelty, and second that elevated contrast enhances learning about a novel color. More generally, the observations are consistent with the idea that elevated contrast attracts attention, thereby enhancing both initial responses - whether positive or negative - and the rate of learning.