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Abstract
Ball catching involves predicting the time and place of arrival of a mobile object. Visual cues of various kinds may help a ball catcher to perform this task successfully. The aims of the present study were (a) to assess the role of the environment in the spatiotemporal planning of ball-catching movements and (b) to determine what specific cues are actually used for this purpose. In the first experiment described here, subjects' catching performances were compared under four different environmental conditions, namely, normal lighting, ultraviolet light with no background, ultraviolet light with a densely structured background, and ultraviolet light with a sparsely structured background. Our results showed that the sight of the mobile object alone does not provide enough information for a subject to achieve his maximum performance level. Accurately assessing the point of arrival of the ball requires the use of relative visual cues. The environment is also a source of visual cues used to assess the time of arrival of the ball. A second experiment was carried out with a view to determining the exact nature of the visual cues used. Here, the orientation (frontal vs. oblique plane) and the apparent visual angle (6° vs. 42°) of the background were made to vary. The results of this experiment showed that the orientation of the background affected the percentage of spatial errors produced by the subjects, whereas the apparent visual angle affected the percentage of temporal errors. The relative velocity cue generated by the masking of successive structures in the environment by the oncoming ball seems to have been taken into account in estimating the time of arrival of the ball. This cue seems to be of crucial importance during the 200 ms prior to the time of contact between the ball and the subject's hand. This finding supports the idea that the method used to assess the time to contact may involve velocity information.
