Perceived Size of a Moving Target



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There is an extensive literature on size perception, but we know much less about the perception of motion trajectories. It is important we examine this more closely because perceiving trajectory size is not a trivial task. For example, Sinico et al. (2009) showed that people underestimate the size of a trajectory on which a dot is moving. In this study, we investigated how well people discriminate the size of a trajectory when compared to their size judgement of a stationary circle. In Experiment 1, we examined the perceived size of a trajectory of a dot moving 360° around a circular path. Experiment 2 examined how accurate people were at this task when the dot moved only a portion of the path, ranging from 90° to 355°. Experiment 3 examined accuracy when the dot moved in an arc exactly as in Experiment 2, but with the speed also randomized. Experiment 4 examined how accurately people judge the sizes of stationary circles with the same radii used to form the trajectories in the previous experiments. Results: people are less accurate at discriminating sizes across all motion conditions when compared to the stationary circle. They were even less accurate when the full trajectory was not transversed. Surprisingly, the speed of the traveling dot had little effect on participants‘ discrimination, which is interesting because one method of discrimination for this task is to use the speed of the moving dot to aid in the size judgement. This suggests that people are able to perform reasonably well on this task even without the aid of speed discrimination.

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Journal of Vision