Overcoming the ceiling effects of experts' motor expertise through active haptic training

Abstract

One of the most challenging issues among experts is how to improve motor skills that have already been highly trained. Recent studies have proposed importance of both genetic predisposition and accumulated amount of practice for standing at the top of fields of sports and performing arts. In contrast to the two factors, what is unexplored is how one practices impacts on experts' expertise. Here, we show that training of active somatosensory function (active haptic training) enhances precise force control in the keystrokes and somatosensory functions specifically of expert pianists, but not of untrained individuals. By contrast, training that merely repeats the task with provision of error feedback, which is a typical training method, failed to improve the force control in the experts, but not in the untrained. These findings provide evidence that the limit of highly trained motor skills could be overcome by optimizing training methods.

Fig. 1. Overview of the haptic system and results of experiment 1.

(A) A three-dimensional model of the haptic system used in the present study. The haptic device was attached to a piano key and pulled the key during the key depression. (B) A representative data of how and when the haptic device loads the key during a keystroke. The black and red lines represent the vertical key motion of the piano key and the external load added to the piano key by the haptic device, respectively. The haptic device loaded the key during descending the key. (C) Group means of the point of subjective equality (PSE) at each of the three sessions are plotted for the three groups (black, training; red, rest; blue, control group). **Inter-session comparisons in the training group, P < 0.01. †Training versus rest group, P < 0.01. #Training versus control group, P < 0.01. (D to F) The probabilities of answering “feels heavier than the unloaded key” are plotted as a function of each external load added by the haptic device. Black, red, and blue lines represent the data obtained at the pre-, post0, and post30 sessions, respectively. The shaded areas show the range calculated by the mean ± SEM. (G) Time courses of the tapping rate during the tapping task in the three groups (black, training; red, rest; blue, control group). $$Multiple comparisons for the main effect of the session factor, P < 0.01. (H and I) Time courses of the error index for the force production task in the three groups when the target was 30% (H) and 70% of the MVK (I). The small and large values indicate accurate and inaccurate performance, respectively. **Inter-session comparisons in the training group, P < 0.01.

Fig. 2. Results of the sensory and motor tests in experiment 2.

(A and B) The PTs assessed by the weight discrimination task (A) and the error index assessed by the low-force production task (B) in the three groups (black, FB; red, no-FB; blue, NM groups). The left and right panels show the results for the index finger and the ring finger, respectively. “B” and “A” displayed on the axis of abscissa indicate “before training” and “after the training,” respectively. Each thin line represents individual data, and each bold line indicates group mean data. **Inter-session comparisons in the training group, P < 0.01. † and ‡ indicate results of the main effect of the group factor, # indicates results of the multiple comparison in the post-session, and * indicates results of the inter-session comparison in the FB group. P < 0.05. ‡‡No-FB versus NM groups for the main effect of the group factor, P < 0.05, P < 0.01. (C) A scatter plot between the PT and error index of the low-force production task at the pre-session in the pianist. The black dashed line indicates a regression line, and the gray dashed lines represent the 95% CI of the regression.

Fig. 3. The error index assessed by the low-force production task before and after motor training in experiment 3.

Each colored line represents the groups (black, pianists; blue, nonmusicians), and the left and right panels show the results for the index finger and the ring finger, respectively. *,**Inter-session comparisons in the nonmusicians group, P < 0.05, P < 0.01.