We noted in Chapter II that the investigations of Hubel and Wiesel of the visual mechanisms in some animals demonstrated the special sensitivity of certain cortical cells to movement. It seems probable that human beings also from infancy upwards rapidly become aware of any movement in their surroundings, before they identify the object in movement. Also there is an immediate response to movement perception, of turning the head and eyes and directing them towards the moving object, fixating it and viewing it attentively in order to discover what it is and what is its direction of movement. Though perception of form in peripheral vision is blurred, any movement is quickly perceived there. However, Cohen (1965) found that peripheral perception of moving objects rapidly habituated; a continuous sequence of dots moving vertically appeared to slow down and stop within fifteen to a hundred seconds. Larger objects continued to appear in movement for a longer period, and horizontal bands, though they slowed down, did not stop altogether. The further out in the periphery the moving objects were presented, the sooner the movement ceased to be perceived. On the other hand, there was no such cessation of movement perception in foveal vision. Cohen hypothesized that in the periphery there was an immediate sensory response such as that discovered by Hubel and Wiesel, which rapidly habituated. But in the fovea there was additionally a clear per-

ception of forms changing position in relation to the spatial framework, which persisted indefinitely. Therefore in normal circumstances the immediate response to movement as such is extended and modified by the perception of particular objects moving in various ways; and it is this latter form of perception which is often affected by relation to the environmental setting, and indeed in some cases to the nature of the objects in movement.