Reduced plantar sole sensitivity facilitates early adaptation to a visual rotation pointing task when standing upright

Abstract

Humans are capable of pointing to a target with accuracy. However, when vision is distorted through a visual rotation or mirror-reversed vision, the performance is initially degraded and thereafter improves with practice. There are suggestions this gradual improvement results from a sensorimotor recalibration involving initial gating of the somatosensory information from the pointing hand. In the present experiment, we examined if this process interfered with balance control by asking participants to point to targets with a visual rotation from a standing posture. This duality in processing sensory information (i.e., gating sensory signals from the hand while processing those arising from the control of balance) could generate initial interference leading to a degraded pointing performance. We hypothesized that if this is the case, the attenuation of plantar sole somatosensory information through cooling could reduce the sensorimotor interference, and facilitate the early adaptation (i.e. improvement in the pointing task). Results supported this hypothesis. These observations suggest that processing sensory information for balance control interferes with the sensorimotor recalibration process imposed by a pointing task when vision is rotated.

Keywords: Linearization; proprioception; sensorimotor conflict; sensorimotor recalibration; visuomotor adaptation.

Figure 1

Representative trajectory and velocity-time curves from one participant. A) A movement to the -30° target with normal vision is presented. The shaded circles are presented for illustrative purposes only as for each pointing only the target (open circle) and a “+” cursor indicating the real-time position of the index finger (without any feedback about the trajectory) were seen by the participant. B) A movement to the -30° target with a 60° visual rotation within the first block of trials is illustrated. The target seen by the participant is illustrated by the open circle. The solid curve illustrates the trajectory seen by the participant (from the displacement of the cursor on the screen). To reach the target, however, the participants had to move 60° clockwise; the trajectory produced by the participant is illustrated by the dotted line. The difference observed in the starting position arises from an initial position distant from the center of the external referential. C) A movement to the -30° target with a 60° visual rotation within the last block of trials is illustrated. D) Velocity-time curves for the three trials are presented. All trials are synchronized on the movement onset.

Figure 2

Movement time (mean ± SE; ms) for the UPRIGHT and UPRIGHT-COLD groups for the baseline, adaptation and post adaptation conditions. All five targets were presented within each block.

Figure 3

Movement time (mean ± SE; ms), distance error (mean ± SE; % in excess of the shortest distance), and accuracy (mean ± SE; %) for the UPRIGHT and UPRIGHT-COLD groups for the baseline, early adaptation (first two blocks), late adaptation (last two blocks), and post adaptation conditions. All five targets were presented within each block.

Figure 4

Angular error (mean ± SE; deg) for the UPRIGHT and UPRIGHT-COLD groups for the baseline, early adaptation (first two blocks), late adaptation (last two blocks), and post adaptation conditions. All five targets were presented within each block