Intercepting moving targets: does memory from practice in a specific condition of target displacement affect movement timing?

Continuously updating one’s predictions underlies successful interception

This paper reviews our understanding of the interception of moving objects. Interception is a demanding task that requires both spatial and temporal precision. The required precision must be achieved on the basis of imprecise and sometimes biased sensory information. We argue that people make precise interceptive movements by continuously adjusting their movements. Initial estimates of how the movement should progress can be quite inaccurate. As the movement evolves, the estimate of how the rest of the movement should progress gradually becomes more reliable as prediction is replaced by sensory information about the progress of the movement. The improvement is particularly important when things do not progress as anticipated. Constantly adjusting one’s estimate of how the movement should progress combines the opportunity to move in a way that one anticipates will best meet the task demands with correcting for any errors in such anticipation. The fact that the ongoing movement might have to be adjusted can be considered when determining how to move, and any systematic anticipation errors can be corrected on the basis of the outcome of earlier actions.

How the required precision influences the way we intercept a moving object

Do people perform a given motor task differently if it is easy than if it is difficult? To find out, we asked subjects to intercept moving virtual targets by tapping on them with their fingers. We examined how their behaviour depended on the required precision. Everything about the task was the same on all trials except the extent to which the fingertip and target had to overlap for the target to be considered hit. The target disappeared with a sound if it was hit and deflected away from the fingertip if it was missed. In separate sessions, the required precision was varied from being quite lenient about the required overlap to being very demanding. Requiring a higher precision obviously decreased the number of targets that were hit, but it did not reduce the variability in where the subjects tapped with respect to the target. Requiring a higher precision reduced the systematic deviations from landing at the target centre and the lag-one autocorrelation in such deviations, presumably because subjects received information about smaller deviations from hitting the target centre. We found no evidence for lasting effects of training with a certain required precision. All the results can be reproduced with a model in which the precision of individual movements is independent of the required precision, and in which feedback associated with missing the target is used to reduce systematic errors. We conclude that people do not approach this motor task differently when it is easy than when it is difficult.

Fast-ball sports experts depend on an inhibitory strategy to reprogram their movement timing

The purpose of our study was to clarify whether an inhibitory strategy is used for reprogramming of movement timing by experts in fast-ball sports when they correct their movement timing due to unexpected environmental changes. We evaluated the influence of disruption of inhibitory function of the right inferior frontal gyrus (rIFG) on reprogramming of movement timing of experts and non-experts in fast-ball sports. The task was to manually press a button to coincide with the arrival of a moving target. The target moved at a constant velocity, and its velocity was suddenly either increased or decreased in some trials. The task was performed either with or without transcranial magnetic stimulation (TMS), which was delivered to the region of the rIFG. Under velocity change conditions without TMS, the experts showed significantly smaller timing errors and a higher rate of reprogramming of movement timing than the non-experts. Moreover, TMS application during the task significantly diminished the expert group's performance, but not the control group, particularly in the condition where the target velocity decreases. These results suggest that experts use an inhibitory strategy for reprogramming of movement timing. In addition, the rIFG inhibitory function contributes to the superior movement correction of experts in fast-ball sports.

Influence of practice with within-trials and inter-trials changes of target velocity in improving movement correction

In the present study, the influences of two practice methods on movement correction during interceptive action was examined. Fourteen men practiced intercepting a moving virtual target. One group practiced on a target that changed velocity from 4 to 8 m/sec. during the trial (within-trials change group). The other group practiced under Slow and Fast conditions, in which the initial velocity (4 or 8 m/sec.) remained constant (inter-trials change group). After the practice, both groups showed similar decreases in temporal errors in interception of an acceleration target. However, the within-trials change group showed non-corrected movements, whereas the inter-trials change group showed corrective movements. Thus, the practice methods for within-trials and inter-trials change resulted in different corrective strategies to acceleration target.

Experts in fast-ball sports reduce anticipation timing cost by developing inhibitory control

The present study was conducted to examine the relationship between expertise in movement correction and rate of movement reprogramming within limited time periods, and to clarify the specific cognitive processes regarding superior reprogramming ability in experts. Event-related potentials (ERPs) were recorded in baseball experts (n=7) and novices (n=7) while they completed a predictive task. The task was to manually press a button to coincide with the arrival of a moving target. The target moved at a constant velocity, and its velocity was suddenly decreased in some trials. Under changed velocity conditions, the baseball experts showed significantly smaller timing errors and a higher rate of timing reprogramming than the novices. Moreover, ERPs in baseball experts revealed faster central negative deflection and augmented frontal positive deflection at 200ms (N200) and 300ms (Pd300) after target deceleration, respectively. Following this, peak latency of the next positive component in the central region (P300b) was delayed. The negative deflection at 200ms, augmented frontal positive deflection, and late positive deflection at 300ms have been interpreted as reflecting stimulus detection, motor inhibition, and stimulus-response translation processes. Taken together, these findings suggest that the experts have developed movement reprogramming to avoid anticipation cost, and this is characterized by quick detection of target velocity change, stronger inhibition of the planned, incorrect response, and update of the stimulus-response relationship in the changed environment.