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Brett Fajen, Gabriel Diaz, Christopher Cramer; Reconsidering the role of action in perceiving the catchability of fly balls. Journal of Vision 2008;8(6):621. doi: 10.1167/8.6.621.
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Many visuomotor tasks require actors to make rapid decisions about different categories of action. For example, pedestrians must decide whether to cross the street in front of an approaching vehicle or wait until it passes; fielders must decide whether to catch a ball on a fly or let it bounce. In both cases, the actor's locomotor capabilities partly determine which actions are possible, and therefore must be taken into account. Previous studies suggest that people only know their locomotor capabilities when they are actually moving, and that stationary observers cannot reliably discriminate between actions that are within and beyond their limits. In one study, subjects made more accurate judgments of the “catchability” of fly balls when they were allowed to move for 1 s compared to when they were stationary. However, there were other differences between the Move and Stand conditions in this experiment that may explain why subjects were more accurate when moving. When we controlled for these differences in the present study, we found that stationary and moving subjects made equally accurate judgments. Fourteen subjects participated in the experiment, which was conducted in a large area virtual environment. Virtual balls were projected to one of four landing locations, crossed with four flight times. On judgment trials, the ball disappeared after 1 s and subjects indicated whether they could have caught the ball. On catch trials, the ball remained visible and subjects attempted to catch the ball. In separate blocks of trials, subjects made judgments while stationary or while moving. Judgments were equally accurate regardless of whether subjects were stationary or moving, suggesting that people do know their locomotor capabilities even when standing still. Judgments also became more accurate as remaining flight time decreased, suggesting that the ability to perceive possibilities for action improves as the task unfolds.
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