Lateral asymmetries during responses to novel-coloured objects in the domestic chick: A developmental study

Chicks were trained to peck on a small coloured (red or green) box for food reinforcement. They were then presented with one box identical to that used during training (familiar) and one of a different colour (unfamiliar). Food reinforcement was delivered for pecking either box, and the right-left position of the two boxes was alternated at random between trials. The number of times chicks pecked at the novel box when it was located on their right or on their left side was recorded. Chicks showed a general tendency to peck more frequently at the novel box when it was located on their right side. The lateral asymmetry was, however, age-dependent. Maximum lateral bias with both red and green novel boxes was observed at around day 4 and day 11 in both sexes, and minimum at around days 7/8 in males and days 8/9 in females. It is suggested that these lateral asymmetries can be accounted for in terms of a head-and-body turning bias associated to preferential use of the lateral field of vision of the left eye, which arises from specializations of the contralateral brain structures (i.e. right hemisphere involvement in response to novelty). The observed changes in lateral asymmetries during development appear, in fact, to fit very well with Independent behavioural and pharmacological evidence for biases to left eye use on day 11, and right eye use on day 8.