Neural mechanisms in visual guidance of limb movement.

Limb movements may be coordinated and executed entirely in the absence of vision. Normally, however, visual impressions play an important role in directing motor response. Sometimes visual direction appears merely as a superimposition upon already established patterns of activity. In progression, obstacles or irregularities seen in the path may condition final placement of the limbs. At other times visual direction appears to enter more intimately to define the particulars of movements from their inception. Reaching out to grasp a glass of water or to seize a fleeting object requires a close correlation of vision with patterning of action. Little is known of the neural organizations through which visual information may impinge upon motor mechanisms. In the absence of definite knowledge brain schemata have been proposed to suggest possible pathways and centers through which visuomotor coordination might occur. Most schemata have implied a transmission of visual information from the visual receptive