Visual lateralisation, form preferences, and secondary imprinting in the domestic chick

Newly hatched chicks (Exp. 1) were exposed to an imprinting object of a certain shape (sphere/cylinder) on Day 1 (primary imprinting) and then to a different-shaped object (cylinder/sphere) on Day 2 (secondary imprinting). They were tested on Day 3 for preferences between primary and secondary imprinting objects in binocular and monocular conditions. Right-eyed males, but not females, showed relatively stronger preferences for the primary imprinting object than left-eyed males; however, the asymmetry was modulated by a spontaneous preference for the sphere. In Experiment 2, a more traditional imprinting paradigm was used: chicks were exposed to the same object for the first 2 days, and on Day 3 underwent a free-choice test between the imprinting object (sphere/cylinder) and a novel one (cylinder/sphere). Results showed that no asymmetries in the use of eyes were apparent, only a general preference for the sphere. In Experiment 3 chicks were exposed, as in Experiment 1, to a primary (Day 1) and a secondary (Day 2) imprinting object; on Day 3 they were exposed to both objects simultaneously; they were also tested for preferences for the two stimuli on Day 4. Left- and right-eyed chicks showed different choice, with the latter preferring the cylinder, thus showing that the eye-asymmetry was in some way peculiar to the secondary imprinting procedure.