Lateralization of a food search task in the domestic chick.

Monocularly occluded Warren sex-linked domestic chicks (Gallus domesticus) were presented with a search test which required the differentiation of familiar food grains from unfamiliar pebbles bearing a strong resemblance to food. Male and female chicks using their left eye performed this discrimination significantly more poorly than did chicks using their right eye, both during learning and after asymptotic performance was reached. This left/right difference was superimposed upon a difference between the sexes, with females pecking fewer pebbles than males. Because of the complexity of the search test utilized, it is difficult to determine whether the left/right difference found is attributable to lateralization of visual discrimination ability or to other factors, such as lateralized differences in food search pattern or investigatory responses to novel pebbles. Nevertheless, asymmetric responses of this type provide additional evidence that lateralization of function in the brain, long thought to be a uniquely human phenomenon, is widespread among vertebrates.