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Alessandro Moscatelli, Francesco Lacquaniti; The weight of time: implied gravitational force enhances discrimination of visual motion duration. Journal of Vision 2011;11(11):1217. doi: 10.1167/11.11.1217.
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By means of five different experiments, we studied the anisotropies in the perception of motion duration. In each experiment, a single small target accelerated over a fixed-length path in one of four different directions in a fronto-parallel plane. Observers were asked to report whether a given test duration was longer or shorter than the standard duration. In Experiments 1 and 2, the directions were downward, upward, rightward, or leftward. In Experiment 1, target motions were superimposed on a computer-graphics pictorial scene, whereas in Experiment 2 the same motions were superimposed on a quasi-uniform background. In Experiments 3 and 4, the target moved along oblique lines, rotated by 45° relative to the cardinal axes, on the non-pictorial background. Finally, in Experiment 5 we used the same pictorial background and target motions as in Experiment 1, but we tilted the monitor and the scene by 45° to assess the role of the scene reference frame. We found systematic anisotropies in the precision of the responses, the performance being better for downward motion than for upward motion in all experiments. In the absence of pictorial cues, the difference in precision between downward and upward motion was much greater when the motion direction was aligned with the physical vertical (Experiment 2) than when it was tilted by 45° (Experiments 3 and 4). In the presence of pictorial cues, instead, the down/up difference in precision was comparable when the down direction defined by pictorial cues was aligned with the physical vertical (Experiment 1) or when it was tilted by 45° (Experiment 5). Moreover, only with pictorial cues was the discrimination in the downward direction systematically superior to that in the orthogonal directions. We argue that implicit knowledge about the effects of ubiquitous gravity force is incorporated in the neural mechanisms computing elapsed time.
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