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Brett Fajen, Jon Matthis, Chris Cramer; Do actors pick up information on the fly to perceive possibilities for action?. Journal of Vision 2009;9(8):1142. doi: 10.1167/9.8.1142.
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Navigating through complex, dynamic environments requires actors to choose actions in ways that take into account their ever-changing movement capabilities. For example, deciding whether to pass through a gap between a pair of converging obstacles requires one to take into account both the state of the environment and one's locomotor capabilities. To what extent does the ability to take movement capabilities into account reflect what actors know about their locomotor capabilities versus what they learn based on information that is picked up “on the fly” while moving? We ran two experiments in which subjects judged whether they could pass through a shrinking gap between a pair of converging cylinders in a virtual environment. Distance to the convergence point and cylinder speed were manipulated such that the gap was passable on some trials but not others. In Experiment 1, judgments of passability were equally accurate regardless of whether judgments were made while subjects were stationary or moving, suggesting that actors can rely on what they know about their locomotor capabilities to make accurate judgments. To further test the contribution of information picked up on the fly, we ran a second experiment in which subjects walked for 3 m before the cylinders began converging. The task was to judge within 1 s after the onset of cylinder motion whether the gap was passable. On a small percentage of catch trials, the visual gain in the virtual environment was increased such that subjects moved 150% faster than normal. Subjects were more likely to perceive the gap as passable on catch trials with increased visual gain. The findings suggest that actors can rely on what they know about their locomotor capabilities to make accurate judgments before movement is initiated, but that visual information also contributes when judgments are made on the fly.
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