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Abstract:
We investigated whether velocity information is used to predict the target’s position when hitting moving targets. Subjects hit spiders which ran from the left to the right at three different velocities. The spiders disappeared from view after 150, 250 or 350 ms. The distance that subjects hit ahead of the disappearing point depended on the spider’s velocity. This was even so for the shortest presentation time. Thus, target velocity is used. However, spiders that disappeared at different times but moved at the same speed were hit at different positions. This means that the differences in target velocity are only partly accounted for. Two models seem to be able to explain the present data reasonably well. The first assumes that velocity is not really used to predict the target’s position, but that the position at which the target disappeared is misperceived in the direction of ocular pursuit. The second proposes that target velocity is used to predict the position at which to hit, but that such information gradually becomes available during the target presentation. To discriminate between these models, we conducted a second experiment in which the presentation time and time between disappearance and hit were varied independently. According to the first model, spiders that are presented for different times but are hit equally long after disappearance, will be hit at the same position. The second model predicts that long presentation times will result in small hitting errors, independent of the time between disappearance and hit. The results were inconsistent with both models.
