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Y Chen, N Matthews, N Qian; Attention Affects Motion Repulsion . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3870.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Motion repulsion refers to the phenomenon that when two different motion directions are presented simultaneously, observers tend to misjudge each direction as further away from the other. Recent studies have shown that attention can increase neurons' sensitivity and enhance observers' ability to perceive properties of the attended objects. We therefore investigated whether attention could reduce the directional misjudgment in motion repulsion. Methods: Three stimulus conditions were employed: an attentional condition plus two control conditions. In the attentional condition, two sets of moving dots with different directions (+/- 22.5 deg from horizontal), but the same speed (2 deg/sec), were presented. At a random time from 400 to 800 ms and in randomly mixed trials, the upper motion either slowed down to 1 deg/sec, had no change, or sped up to 3 deg/sec, for 200 ms, and then returned to the initial speed for 300 ms. The speed of the lower motion was constant. Subjects pressed a key to terminate the stimulus as soon as they detected a speed change, or waited for the stimulus to disappear if no speed change was detected. Subjects had to respond within the time window of 200 to 500 ms after the actual speed change. A trial was aborted if subjects responded outside this time window, or responded when there was no actual speed change. Audio feedbacks were provided for the aborted trials. For the correct trials, after a 1-sec ISI, a single set of moving dots was shown. Subjects were then required to adjust the motion direction online to match the perceived direction of the upper motion in the first stimulus of that trial. The first control condition measured the normal motion repulsion; the stimuli were identical to those for the attentional condition but subjects were instructed to ignore any speed change (two-motion control). In the second control condition, the lower motion in the first stimulus of each trial was not shown at all (single-motion control). The stimulus duration of the control conditions matched the mean duration of the attentional condition. All other aspects of the two control conditions were identical to those of the attentional condition. Results: The mean repulsion values of four observers were 1.8 deg, 6.5 deg and -0.4 deg for the attentional, two-motion control and single-motion control conditions, respectively. Repulsion was significantly greater in the two-motion control condition than in either the attentional condition or the single-motion control condition (p<0.005), which were not significantly different from each other (p=0.08). Conclusion: Attention significantly reduces motion repulsion.
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