Lateralization in chicks and hens: new evidence for control of response by the right eye system.

Domestic chicks show marked lateralization of visually evoked behaviour: left eye use is associated with, and has advantage for, the detection of novelty; right eye use is associated with the use of selected cues to determine what response should be given. Experiments undertaken to see how far such lateralization might be a transient feature of development showed similar patterns in both adults and chicks: (i) use of the right, but not the left, frontal field allowed the inhibition of pecks at a familiar social partner; (ii) in distant viewing, there was spontaneous preference for more use of the left eye when the social partner was familiar rather than unfamiliar. The chick data, in particular, support the hypothesis that the visual system fed by the right eye is especially competent in the control of response. This is shown by the ability of birds that are using the right eye to inhibit approach to an entirely novel potential social partner, and inhibit pecks at a familiar partner. The resemblances between chick and hen are sufficient to show that the basic adult pattern is already present in the young chick: the various developmental changes in features of lateralization, such as days of bias to control by one or other hemisphere, thus do not cause the appearance of the adult pattern.