The development of visual lateralization in the domestic chick

In the domestic chick the visual systems fed by right and left eye differ already on day 2 in the way in which they analyse stimuli. The right eye system (RES) tends to use conspicuous cues to assign stimuli to categories whilst the LES is interested in all properties of stimuli including position in space. As early as testing is possible, the LES shows advantage in the use of topographical cues, and the RES in distinguishing food from other targets. Sharp changes in the ability of RES or LES to take charge of behaviour follow: on day 8 RES controls response even in tasks where the LES usually has advantage. Rapid change then follows: by day 10 the LES is able to control behaviour under appropriate conditions. In natural broods the sudden appearance of exploration away from the mother on day 10 may result from this change. Such periods of control by one eye system may allow intensive appropriate learning. The timing of the transition is the same in both sexes, even though females behave in almost all tasks as though the LES were less specialized (or more under the control of RES).