International Journal of Comparative Psychology

Newly-hatched chicks were reared with a coloured imprinting object on day 1 of life (primary imprinting) and then with an object of a different colour (secondary imprinting) on day 2. They were then tested on day 3 for preferences between the primary and the secondary imprinting object in binocular and in monocular conditions. The main results were that (1) left-eyed chicks usually showed clearer choice than right-eyed chicks; (2) there were colour preferences that appeared to affect choice differently in left- and right-eyed chicks; (3) eye asymmetries were in general more pronounced in males than in females. Experiments using composite stimuli (that contained simultaneously the colours of both the primary and the secondary imprinting objects) and experiments in which retention of memories for the primary and secondary imprinting objects were tested against the preference for novel objects showed that the eye asymmetries cannot be explained neither by hemispheric differences in response to novelty nor by different rates of forgetting of primary and secondary imprinting objects in the two hemispheres. It is argued that properties of single-units responses in neural structures involved in imprinting in the left and right hemisphere can account for these behavioural results.