On perceptual biases in virtual object manipulation: Signal reliability and action relevance matter

This study examined the role of visual reliability and action relevance in mutual visual-proprioceptive attraction in a virtual grasping task. Participants initially enclosed either the width or the height of a visual rectangular object with two cursors controlled by the movements of the index finger and thumb. Then, either the height or the width of this object or the distance between the fingers was judged. The judgments of object's size were attracted by the felt finger distance, and, vice versa, the judged finger distance was attracted by the size of the grasped object. The impact of the proprioceptive information on object judgments increased, whereas the impact of visual object information on finger judgments decreased when the reliability of the visual stimulus was reduced. Moreover, the proprioceptive bias decreased for the action-relevant stimulus dimension as compared with the action-irrelevant stimulus dimension. These results indicate sensory integration of spatially separated sensory signals in the absence of any direct spatial or kinematic relation between them. We therefore suggest that the basic principles of sensory integration apply to the broad research field on perceptual-motor interactions as well as to many virtual interactions with external objects.