The fast contribution of visual-proprioceptive discrepancy to reach aftereffects and proprioceptive recalibration

Adapting reaches to altered visual feedback not only leads to motor changes, but also to shifts in perceived hand location; “proprioceptive recalibration”. These changes are robust to many task variations and can occur quite rapidly. For instance, our previous study found both motor and sensory shifts arise in as few as 6 rotated-cursor training trials. The aim of this study is to investigate one of the training signals that contribute to these rapid sensory and motor changes. We do this by removing the visuomotor error signals associated with classic visuomotor rotation training; and provide only experience with a visual-proprioceptive discrepancy for training. While a force channel constrains reach direction 30o away from the target, the cursor representing the hand unerringly moves straight to the target. The resulting visual-proprioceptive discrepancy drives significant and rapid changes in no-cursor reaches and felt hand position, again within only 6 training trials. The extent of the sensory change is unexpectedly larger following the visual-proprioceptive discrepancy training. Not surprisingly the size of the reach aftereffects is substantially smaller than following classic visuomotor rotation training. However, the time course by which both changes emerge is similar in the two training types. These results suggest that even the mere exposure to a discrepancy between felt and seen hand location is a sufficient training signal to drive robust motor and sensory plasticity.York University Librarie

The fast contribution of visual-proprioceptive discrepancy to reach aftereffects and proprioceptive recalibration - Fig 3

<p>Reach aftereffects (solid lines) and proprioceptive localizations (dashed lines) plotted as a function of all blocks (A) and for the first and last block (B) during the rotated condition. No-cursor reaches and proprioceptive localization for the final block of the aligned condition are also shown in at the far left of panel <b>A</b>, the rotated condition results have these baseline data subtracted out to normalize the results. The shaded areas for the curves in <b>A</b> represent a 95% confidence interval. The asterisk in <b>B</b> indicates significant differences between blocks; one star is significant to .01, two stars are significant to .001. Error bars are +/- 1 standard error.</p

Experimental setup and design.

<p><b>A:</b> Side view of the experimental set-up. The top layer is the monitor, middle layer is the reflective screen, and the bottom layer is the touchscreen. The robot is depicted beneath with the participants’ right hand grasping it. <b>B-D:</b> Top views of task specific set-ups. <b>B</b>: <b>Training task.</b> The home position is represented by a green circle with a 1 cm diameter; located approximately 20 cm in front of the subject and not visible during the trial. Targets are represented by yellow circles with a 1 cm diameter located 12 cm radially from the home position at 60°, 90° and 120°. The target was visible for 250 ms, after which it disappeared and participants moved their right hand along the constrained force channel (shown in red) to its remembered location. During rotated exposure training the constrained hand path was rotated 30° CCW from target with respect to the start location: <b>C No-cursor reach task.</b> The same target locations were used as during training. The participant would freely reach, without the force channel that was present during exposure training trials and without the cursor or any other visual feedback of the hand. <b>D: Localization task.</b> In the proprioceptive localization task, the robot passively moved the unseen, right trained hand to one of the three target locations. The participants then used the index finger of their left untrained, visible, hand to indicate the felt location of the right hand, specifically the thumb.</p

Change in proprioceptive localizations across training types.

<p>Mean change in hand proprioception relative to baseline for all blocks (A) and just the first and final block (B) of the classic (green) and exposure (purple) rotated conditions. As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200621#pone.0200621.g003" target="_blank">Fig 3</a>, the final block of the aligned condition is also shown in the far left on panel A and the rotated conditions have the aligned baseline subtracted. <b>A:</b> The dashed lines within the coloured curves represent the block means while the coloured areas represent a 95% confidence interval. In <b>B,</b> the asterisk indicates significant differences between blocks; one star is significant to .01, two stars to .001. The error bars are +/- 1 standard error.</p

Testing session breakdown.

<p>Participants completed three tasks under two separate conditions that include exposure training with an aligned cursor and with a cursor rotated 30° CW. As shown by the four boxes, each block consisted of 18 trials including two sets of 6 exposure training trials, alternatingly followed by 3 no-cursor or 3 localization trials. This amounted to a total of 270 (18 trials X 15 iterations) trials during the <b>aligned condition</b> and 540 (18 trials X 30 iterations) trials during the <b>CW rotation condition</b>. All participants completed the same tasks throughout training, but the order in which the tasks were completed was counterbalanced across participants with two versions of task order <b>(version 1 and version 2)</b>.</p

Reach aftereffects across training types.

<p>Mean change in no-cursor reaches relative to baseline for all blocks (A) and just the first and final block (B) of the classic (green) and exposure (purple) rotated conditions. As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200621#pone.0200621.g003" target="_blank">Fig 3</a>, the final block of the aligned condition is also shown in the far left on panel A and the rotated conditions have the aligned baseline subtracted. <b>A:</b> The solid lines within the coloured curves represent the block means while the coloured areas represent a 95% confidence interval. In <b>B,</b> the asterisk indicates significant differences between blocks; one star is significant to .01, two stars to .001. The error bars are +/- 1 standard error.</p

Time Course of Reach Adaptation and Proprioceptive Recalibration during Visuomotor Learning - Fig 4

<p>Mean changes in hand location at peak velocity and at reach endpoint for each respective task as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163695#pone.0163695.g003" target="_blank">Fig 3</a>, for the first and final block of training in Day 1 <i>(A)</i> and in Day 2 <i>(B)</i>, relative to aligned-training baseline. Error bars represent +/- 1 standard deviation from the average. The line at zero represents baseline performance.</p

Breakdown of experimental set up.

<p><i>Day 1 and Day 2</i> illustrate what conditions participants experienced on which testing day. All participants started with aligned cursor training on Day one then learned one of the two rotations (CCW or CW). All participants then returned one week later for <i>Day two</i> and completed the <i>retention</i> condition (which is described in further detail to the right) and learned the other rotation direction(CW or CCW). All participants completed the same tasks throughout training, but there were two tasks orders, counterbalanced across participants <i>(version 1 and version 2)</i>. Participants completed a total of 270 trials during the aligned-cursor condition and 540 trials during the rotated cursor condition.</p