Evidence that endpoint feedback facilitates intermanual transfer of visuomotor force learning by a cognitive strategy

Abstract

Humans continuously adapt their movement to a novel environment by recalibrating their sensorimotor system. Recent evidence, however, shows that explicit planning to compensate for external changes, i.e., a cognitive strategy, can also aid performance. If such a strategy is planned in external space, it should improve performance in an effector-independent manner. We tested this hypothesis by examining whether promoting a cognitive strategy during a visual-force adaptation task performed in one hand can facilitate learning for the opposite hand. Participants rapidly adjusted the height of visual bar on screen to a target level by isometrically exerting force on a handle using their right hand. Visuomotor gain increased during the task and participants learned the increased gain. Visual feedback was continuously provided for one group, whereas for another group only the endpoint of the force trajectory was presented. The latter has been reported to promote cognitive strategy use. We found that endpoint feedback produced stronger intermanual transfer of learning and slower response times than continuous feedback. In a separate experiment, we found evidence that aftereffects are reduced when only endpoint feedback is provided, a finding that has been consistently observed when cognitive strategies are used. The results suggest that intermanual transfer can be facilitated by a cognitive strategy. This indicates that the behavioral observation of intermanual transfer can be achieved either by forming an effector-independent motor representation or by sharing an effector-independent cognitive strategy between the hands.NEW & NOTEWORTHY The causes and consequences of cognitive strategy use are poorly understood. We tested whether a visuomotor task learned in a manner that may promote cognitive strategy use causes greater generalization across effectors. Visual feedback was manipulated to promote cognitive strategy use. Learning consistent with cognitive strategy use for one hand transferred to the unlearned hand. Our result suggests that intermanual transfer can result from a common cognitive strategy used to control both hands.

Keywords: cognitive strategy; intermanual transfer; visual feedback; visuomotor adaptation; visuomotor gain.

Graphical abstract

Figure 1.

Task structure and single-trial results. A: visual feedback (VF) trials in continuous visual feedback (CVF) groups, where isometric wrist force was continuously shown on screen as the height of a black bar. B: for endpoint feedback (EPF) groups, during visual feedback trials force was displayed as a static black bar, which appeared once the wrist extension was completed. C: “No visual feedback trials” (noVF) were identical for all groups and involved participants making wrist extensions of appropriate strength in the absence of any visual feedback. D: the experiment had a baseline, learning, and test phase, each with 3 blocks of 48 trials. In the baseline phase, participants alternated between sets of 9 “visual feedback trials” and 3 “no visual feedback trials,” using either the right or left hand (pseudorandomized). During the learning phase, visuomotor gain increased from 1 to 3, either abruptly (abrupt gain change groups), or via linear increments across visual feedback trials (gradual gain change groups). Left hand visual feedback (LVF) trials were absent during the learning and test phase, meaning that the gain change was only experienced directly when using the right hand. E: a single representative right hand trial from a participant in one of the CVF groups, showing force increase toward the visual target in response to the go signal. F: a representative right hand trial from an EPF group participant, showing force increase toward the visual target in response to the go signal. LnoVF and RnoVF, no visual feedback trials with the left and right hand, respectively; RVF, right hand visual feedback.

Figure 2.

Experiment 1. Transfer, learning, and reaction time results. A: percentage transfer between RnoVF and LnoVF in each group across the entire experiment. In the endpoint feedback (EPF) groups the amount of transfer returned to around 85% during the learning phase, but in the continuous visual feedback (CVF) groups remained around 30% through to the end of the test phase. Inset box plots show that mean transfer percentage at baseline did not differ across groups but was significantly higher in the EPF groups than the CVF groups during the test phase (n.s., not significant, ***P < 0.001, n = 56). B: percentage learning of gain change relative to baseline performance on right hand feedback (RVF) trials in each group across the entire experiment. Inset box plot shows that learning rates did not significantly differ across groups during the test phase (n.s., not significant, n = 56). C: percentage learning of gain change relative to baseline performance on RnoVF trials in each group across the entire experiment. Inset box plot shows that the mean performance at test did not differ across groups (n.s., not significant, n = 56). D: response times on RVF trials for all groups across the entire experiment. RT was slower in EPF compared with CVF groups at baseline and test (*P < 0.05, n = 56). Abr., abrupt; Grad., gradual., LnoVF, left hand no feedback; RnoVF, right hand no feedback.

Figure 3.

Design and results of experiment 2. A: design of experiment 2 showing how visuomotor gain changed across blocks (B1–B10). On the 10th trial of B9, there was sudden gain change that returned the gain to the baseline level. During this aftereffect phase, trials alternated between two visual feedback (VF) trials followed by one no visual feedback (noVF) trial. B: signed error ratio after subtracting baseline values for noVF trials in the aftereffect phase, showing larger overshooting for continuous visual feedback (CVF) than endpoint feedback (EPF) groups, consistent with larger aftereffects. Box plot shows that the degree of overshoot was significantly higher for the CVF group relative to the EPF group, indicative of a greater aftereffect (**P < 0.01, n = 29). C: signed error ratio after subtracting baseline values for visual feedback (VF) trials in the aftereffect phase for CVF and EPF groups. Inset shows that there was no significant difference between the two groups (n.s., not significant, n = 29). D: right hand feedback (RVF) learning percentage across entire experiment for CVF and EPF groups. Note that both groups were able to maintain performance accuracy close to 100% from the baseline to the test phase. Inset shows that learning percentage at test was significantly higher in the CVF group compared with the EPF group (*P < 0.05, n = 29). E: mean reaction time (RT) across entire experiment for CVF and EPF groups. Left box plot shows that overall RT was significantly slower in the EPF group compared with the CVF group. Right box plot shows that the CVF group increased their RT on VF trials from the test phase to the aftereffect phase to a greater extent than the EPF group (*P < 0.05, ***P < 0.001, n = 29).