Footedness in binocular and monocular chicks.

The first foot used during bouts of ground scratching in 16-day-old chicks searching for food in the floor of an arena covered with sawdust was recorded in animals with normal binocular vision and in animals with an eye temporarily occluded by an eye-patch. Binocular chicks showed a significant right foot bias, whereas monocular chicks tended to use the foot contralateral to the eye in use. Data for monocular chicks thus suggest that the activated hemisphere (contralateral to the eye in use) is the one that takes control of posture, leaving to the other hemisphere reflex-like responses associated with ground scratching or body wiping. It is argued that footedness in chicks might have arisen from the limb that is used to maintain postural and positional control, rather than from the limb that is used during motor activities.