Large adjustments in visually guided reaching do not depend on vision of the hand or perception of target displacement

Abstract

When we reach towards an object that suddenly appears in our peripheral visual field, not only does our arm extend towards the object, but our eyes, head and body also move in such a way that the image of the object falls on the fovea. Popular models of how reaching movements are programmed have argued that while the first part of the limb movement is ballistic, subsequent corrections to the trajectory are made on the basis of dynamic feedback about the relative positions of the hand and the target provided by central vision. These models have assumed that the adjustments are dependent on seeing the hand moving with respect to the target. Here we present evidence that a change in the position of a visual target during a reaching movement can modify the trajectory even when vision of the hand is prevented. Moreover, these dynamic corrections to the trajectory of the moving limb occur without the subject perceiving the change in target location. These findings demonstrate that visual feedback about the relative position of the hand and target is not necessary for visually driven corrections in reaching to occur, and the mechanisms that maintain the apparent stability of a target in space are dissociable from those that mediate the visuomotor output directed at that target.

Sources of variability in interceptive movements

“…We realize that planning is often considered to end at the moment the arm begins to move (although it is not at all evident that the way that movements are controlled changes fundamentally at that moment) while corrections to the arm movements are often attributed to feedback about the movement itself rather than to changes in the plan (although updates of the target position can be just as effective at guiding the hand; Brenner and Smeets 2003;Goodale et al 1986). However, since we anyway have no way to tell how long in advance differences at the time of impact were planned, or whether they emerged from corrections to earlier errors, we will simply refer to both as being 'planned'.…”

Looking for the agent: an investigation into consciousness of action and self-consciousness in schizophrenic patients

“…Subjects may correct visuomotor errors toward targets that they have not perceived (e.g. Bridgeman et al, 1981;Goodale et al, 1986). They may also make perceptual judgements on visual objects, that are in contradiction with their movements directed towards the same objects (e.g.…”

Frames of Reference for Perception and Action in the Human Visual System

“…The dissociation between motor adjustment and perceptual report has also been demonstrated in experiments in which the position of a target is moved unpredictably during a saccadic eye movement (7,8,28,32). In these experiments, subjects typically fail to report the change in the position of the target even though a later correction saccade and even a manual aiming movement directed at the target will accurately accommodate the shift in position.…”

“…Support for this idea came from an experiment by Goodale et al (28) in which the position of a target was changed unpredictably during the execution of the movement. Subjects were asked to move their finger from a central target to a new target (a small light) that appeared suddenly in their peripheral visual field.…”

“…The visuomotor systems computing the saccadic eye movements (or the aiming movements) directed at the target simply ignored the movement of the frame and computed the actual position of the target in retinocentric (and perhaps also in head and/or shoulder-centered) coordinates. In the experiments by Goodale et al (28), in which the position of the target was changed unpredictably during a saccade, the subjects' failure to perceive the displacement of the target was probably a reflection of the broad tuning of perceptual constancy mechanisms: mechanisms which preserve the identity of a target as its position is shifted on the retina during an eye movement. When no other reference points are available in the field of view, the perceptual system assumes that the position of the target (which was stable at the beginning of the saccade) has not changed.…”