Prism exposure aftereffects and direct effects for different movement and feedback times

The effects of movement time and time to visual feedback (feedback time) on prism exposure aftereffects and direct effects were studied. In Experiment 1, the participants' (N = 60) pointing limb became visible early in the movement (.2-s feedback time), and eye-head aftereffects increased with increasing movement time (.5 to 3.0 s), but larger hand-head aftereffects showed little change. Direct effects (terminal error during exposure) showed near-perfect compensation for the prismatic displacement (11.4 diopters) when movement time was short but decreasing compensation with longer movement times. In Experiment 2, participants' (N = 48) eye-head aftereffects increased and their larger hand-head aftereffects decreased with increasing movement time (2.0 and 3.0 s), especially when feedback time increased (.25 and 1.5 s). Direct effects showed increasing overcompensation for longer movement and feedback times. Those results suggest that aftereffects and direct effects measure distinct adaptive processes, namely, spatial realignment and strategic control, respectively. Differences in movement and feedback times evoke different eye-hand coordination strategies and consequent direct effects. Realignment aftereffects also depend upon the coordination strategy deployed, but not all strategies support realignment. Moreover, realignment is transparent to strategic control and, when added to strategic correction, may produce nonadaptive performance.     

A perception-action coupling type of control in long jumping

The authors' goal was to identify the control mechanisms used by long jumpers (N = 6) to precisely position their foot at the board. In addition to the intertrial method usually used in previous research, an original method based on a trial-by-trial analysis was also implemented. If the approach to the board in long jumping encompasses two distinct sequences separated by a key step that marks the initiation of visual control, then a trial-by-trial analysis should reveal those sequences, regardless of the amount of adjustment: The step number at which regulation is initiated should be the same irrespective of the amount of adjustment. If, in contrast, a perception-action coupling mechanism operates, then the step number at which regulation is initiated should be a function of the amount of adjustment: A linear relation between those 2 variables should emerge. The results of the present study are compatible with continuous control mechanisms based on a perception-action coupling.