Semantics affect the planning but not control of grasping.

The semantic meaning of a word label printed on an object can have significant effects on the kinematics of reaching and grasping movements directed towards that object. Here, we examined how the semantics of word labels might differentially affect the planning and control stages of grasping. Subjects were presented with objects on which were printed either the word "LARGE" or "SMALL." When the grip aperture in the two conditions was compared, an effect of the words was found early in the reach, but this effect declined continuously as the hand approached the target. This continuously decreasing effect is consistent with a planning/control model of action, in which cognitive and perceptual variables affect how actions are planned but not how they are monitored and controlled on-line. The functional and neurological bases of semantic effects on planning and control are discussed.