Grasping in wonderland: altering the visual size of the body recalibrates the body schema

Abstract

Can viewing our own body modified in size reshape the bodily representation employed for interacting with the environment? This question was addressed here by exposing participants to either an enlarged, a shrunken, or an unmodified view of their own hand in a reach-to-grasp task toward a target of fixed dimensions. When presented with a visually larger hand, participants modified the kinematics of their grasping movement by reducing maximum grip aperture. This adjustment was carried over even when the hand was rendered invisible in subsequent trials, suggesting a stable modification of the bodily representation employed for the action. The effect was specific for the size of the grip aperture, leaving the other features of the reach-to-grasp movement unaffected. Reducing the visual size of the hand did not induce the opposite effect, although individual differences were found, which possibly depended on the degree of subject's reliance on visual input. A control experiment suggested that the effect exerted by the vision of the enlarged hand could not be merely explained by simple global visual rescaling. Overall, our results suggest that visual information pertaining to the size of the body is accessed by the body schema and is prioritized over the proprioceptive input for motor control.

Changing the size of a mirror-reflected hand moderates the experience of embodiment but not proprioceptive drift: a repeated measures study on healthy human participants

“…Thus, recalibration of the representation of the hand was not a necessary requirement when judging the location of the hand (i.e. proprioceptive drift) (Bernardi et al 2013; de Vignemont 2011; Linkenauger et al 2013). …”

Short Term Motor-Skill Acquisition Improves with Size of Self-Controlled Virtual Hands

“…Performance gains increased with the size of the virtual hands but only in the context of visual feedback, when the subjects actively controlled the virtual hand and not in the context of visual input (as in training by observation). Previous studies in motor control showed that participants changed their hand kinematics following changes in hand-size visual feedback [26, 27]. To the best of our knowledge, the current study is the first to demonstrate that rescaling the visual feedback during training can boost the motor performance in humans.…”

“…The size of visual feedback from the body has been previously examined in various domains including pain perception [17, 18, 20], tactile discrimination [13], sense of embodiment [14, 15], and reaching/grasping tasks [26, 31] but not with respect to short term motor skill learning. Here we used VR devices to manipulate the size of virtual hands controlled by the subject, embedded in the real environment as captured by a camera.…”

“…Finally, it has been demonstrated that humans use continuous visual feedback to correct their concurrent finger movements towards a sequence of visually cued targets [23, 24], and that manipulating the size of visual hand feedback induces changes in mean grip aperture in reaching and grasping tasks [25–27]. Taken together, there is ample evidence supporting the view that the size of visual feedback from the body plays a significant role in various domains including action production.…”

A New Neurocognitive Interpretation of Shoulder Position Sense during Reaching: Unexpected Competence in the Measurement of Extracorporeal Space

“…Visual information on the size of the body is accessed by the body schema and is prioritized over proprioceptive inputs for motor control [13]. Articular proprioception, defined as a specialized sensory function that includes the sensation of movement and joint position, must integrate with visual afferents for correct static and dynamic joint activity [14, 15].…”