Mentally Simulated Reaches for Visual Objects: Effects of Stimulus Orientation and Biomechanical Constraints

Abstract

Recent evidence suggests that mentally simulating an action involves many of the same neuropsychological mechanisms as overt performance. A series of experiments were conducted to evaluate whether representations involved in mentally simulated reaches are constrained by the same biomechanical factors that limit actual movements. Subjects were asked to use either the right or the left hand to acquire a dowel presented visually in one of 24 different orientations within the picture plane. In reaching studies, subjects responded by grasping the target using either an overhand or underhand grip; in the mentally simulated studies, subjects responded by vocally indicating whether they would prefer an overhand or underhand grip if they were to actually grasp the object. Results indicate substantial correspondence between actual and mentally simulated reaching. Grip preferences in both situations are highly correlated, and reflect biomechanical constraints on rotation of the forearm. In both actual and mentally simulated tasks, subjects show clear preferences for grips that minimise perceived awkwardness. In contrast to related work, the time required to perform mentally simulated reaches for visual objects was found not to increase linearly with distance from the resting posture of the response hand. Findings are discussed with respect to the hypothesis that actual and mentally simulated actions involve the same internal representations.