Author(s): KUSAFUKA, A., WU, D., KUDO, K., SHIBATA, K., WATANABE, K., SHIMOJO S., Institution: THE UNIVERSITY OF TOKYO, Country: JAPAN, Abstract-ID: 1673

INTRODUCTION:
An urgent situation or pressured environment often makes people perform beyond or below their ordinary performance. These examples suggest that people implicitly set limits on their own performance depending on context. In the field of motor control, people tend to adjust their performance in response to feedback obtained during a motor task. The current study demonstrated that the personal limit can be changed by unwittingly manipulated feedback on one's performance during a pinching force exertion and throwing.
METHODS:
In the pinching task, participants applied their force on a pinching device with the thumb and index fingers for 5 seconds while a time-series of the applied force was displayed on a screen in real time. Each participant exerted the maximum force and 50% of their maximum force on a subjective scale in 3 trials each. Each trial was assigned unwittingly to one of the three feedback types: control (no manipulation), upwards (gradually increased in the second half), or downwards (gradually decreased in the second half). In the throwing task, participants threw a ball toward a net while the ball speed was displayed on a screen. Each participant performed two sets of 10 balls with their maximum effort. Each set was assigned unwittingly to one of the two feedback types: upwards (gradually increased in the second half), or downwards (gradually decreased in the second half). The average of the applied force/ball speed was compared across the period (the first vs. second half of the trials/sets) by a paired t-test.
RESULTS:
In the pinching task, the average force in the last 1sec was significantly larger with the downwards feedback (average increase of 7.9% in maximum force) and smaller with the upwards feedback (average decrease of 7.0% in maximum force) compared to that in the first 1sec of each trial (p<.05). In the throwing task, the average ball speed in the second 5 balls was significantly larger with the downwards feedback (average increase of 1.2km/h) and smaller with the upwards feedback (average decrease of 2.2km/h) compared to that in the first 5 balls of each set (p<.05). These results suggest that the participants under- or over-estimated their own performance due to the unwittingly manipulated feedback, which in turn increased or decreased the applied force.
CONCLUSION:
Our findings suggest that the limit of people’s motor performance can be changed due to changes in the perception of their performance based on the covert manipulation of feedback. With the appropriate use, such feedback manipulation may contribute to the improvement of motor performance and promotion of learning and skill acquisition in various sports fields. On the other hand, it has theoretical implications on how the brain controls its own limit in performance.