The Influence of Visual Feedback and Prior Knowledge About Feedback on Vertical Aiming Strategies

ABSTRACT

Two experiments were conducted to examine time and energy optimization strategies for movements made with and against gravity. In Experiment 1, the authors manipulated concurrent visual feedback, and knowledge about feedback. When vision was eliminated upon movement initiation, participants exhibited greater undershooting, both with their primary submovement and their final endpoint, than when vision was available. When aiming downward, participants were more likely to terminate their aiming following the primary submovement or complete a lower amplitude corrective submovement. This strategy reduced the frequency of energy-consuming corrections against gravity. In Experiment 2, the authors eliminated vision of the hand and the target at the end of the movement. This procedure was expected to have its greatest impact under no-vision conditions where no visual feedback was available for subsequent planning. As anticipated, direction and concurrent visual feedback had a profound impact on endpoint bias. Participants exhibited pronounced undershooting when aiming downward and without vision. Differences in undershooting between vision and no vision were greater under blocked feedback conditions. When performers were uncertain about the impending feedback, they planned their movements for the worst-case scenario. Thus movement planning considers the variability in execution, and avoids outcomes that require time and energy to correct.

Keywords:

• aiming
• vision
• speed-accuracy
• gravity
• energy optimization
• movement planning

ACKNOWLEDGMENTS

The authors thank Dan Garcia for technical help with the experimental setup.

Notes

1. For corrections associated with target undershoots, the limb still has a positive velocity in the direction of the target. When correcting overshoots however, the limb must overcome the inertia of a zero velocity situation at the point of the reversal. Moreover the neuromuscular demands of a reversal are greater than a second acceleration because the roles of the agonist and antagonist muscles groups are changed (Elliott et al., 2010).

2. Both terminal feedback and online feedback can also be used to refine the expected sensory consequences associated the internal model of the aiming movement. These expected consequences can then be compared to online feedback on subsequent trials for impulse control.

3. Although slight compared to no-vision conditions, the difference between the full vision constant error in Experiment 1 (–1.1 mm) and the full vision constant error in Experiment 2 (–5.8 mm) was significant, t(20) = 3.61, p < .01. This difference may be due to the more limited time that participants had to process feedback in Experiment 2. Alternatively, there may be some sort of advantage associated with seeing the hand return to the home position (i.e., Experiment 1).

4. Ferraz de Oliveira, Huys, Oudejans, van de Langenberg, and Beek (2007) and Ferraz de Oliveira, Oudejans, and Beek (2006) found that even skilled basketball players undershoot foul and jump shots to a greater extent when vision of the last portion of the shot is reduced or degraded. Because of the backboard, undershooting is completely maladaptive in this context, but occurs nonetheless.

Additional information

Funding

This research was supported by the Natural Sciences and Engineering Research Council of Canada.