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Serena J. Butcher, Patrick Cavanagh; Within-field advantage for detecting matched motion paths. Journal of Vision 2005;5(8):964. doi: https://doi.org/10.1167/5.8.964.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Butcher & Cavanagh (VSS 04) demonstrated that subjects were faster and more accurate in detecting a pair of repeated letters, colors, or sizes when presented unilaterally (both elements in the same hemifield, left or right) than when presented bilaterally (one element in each hemifield). We now find that the within-field advantage also holds for detecting matched motion paths. Methods: Each trial began with 4 static white 1.5 deg. diameter disks on a gray background, placed at the vertices of an invisible 6 × 6 deg. square around fixation. After a short interval, the disks began to move at a speed of 3.25deg/sec. The display was present for 14 video frames on a 1024 × 768 monitor at 75hz. Each disk could move in one of the four cardinal directions, and maintained its direction of motion for the duration of the display. On target present trials, 2 of the 4 disks had the same motion direction. On target absent trials each of the 4 disks moved in different directions. Subjects reported the presence or absence of matched motions with a keypress. Results: Subjects were 72 ms faster detecting matched motions when the match occurred unilaterally versus bilaterally (t(1,6) = 8.02) p <0.001). There was no evidence of a speed accuracy trade-off (mean misses: unilateral = 4%; bilateral = 8%). Conclusion: The results show that matched motion is more efficiently detected within hemifields than across fields. This suggests that the grouping process underlying the detection of the match operates in early retinotopic areas where the left and right hemifields are divided. This early grouping holds for these transient motion features as well as for the shape and color features reported previously.
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