WEBER'S LAW DURING GRASPING
Visual control of action constitutes a fundamental ability of people when interacting with their visual environment. Visual perception, however, is necessary for recognizing and memorizing different aspects of this environment. Neuroanatomical and neuropsychological evidence supports the notion that different systems mediate visual control of action and visual perception. Here, we will describe a behavioral paradigm to study possible differences in visual sensitivity for object size between visuomotor control and perception. This paradigm is based on applying the measure of Just Noticeable Difference (JND) to the action domain. In a series of experiments, participants were asked to either grasp or make perceptual estimations of objects varying in size. The basic finding throughout all experiments was that Weber's law, a fundamental law governing perception, was violated for visually-guided action throughout the entire movement trajectory. Combining this paradigm with other paradigms used in the literature allows new insights of potential dissociations between the processes underlying perception and action.