Dynamic effects of the Ebbinghaus illusion in grasping: support for a planning/control model of action.

A distinction between planning and control can be used to explain the effects of context-induced illusions on actions. The present study tested the effects of the Ebbinghaus illusion on the planning and control of the grip aperture in grasping a disk. In two experiments, the illusion had an effect on grip aperture that decreased as the hand approached the target, whether or not visual feedback was available. These results are taken as evidence in favor of a planning/control model, in which planning is susceptible to context-induced illusions, whereas control is not. It is argued that many dissociations between perception and action may better be explained as dissociations between perception and on-line control.