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Alex Holcombe, Daniel Linares, Maryam Vaziri-Pashkam; Inability to perceive the spatial relationship of objects revolving too quickly to attentively track. Journal of Vision 2010;10(7):316. doi: 10.1167/10.7.316.
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© ARVO (1962-2015); The Authors (2016-present)
What is perception missing when one cannot attentively track? To find out, we exploit the finding that an object revolving about fixation faster than 1.5 revolutions per second (rps) cannot be tracked (Verstraten, Cavanagh, Labianca 2000). METHODS. Six Gaussian blobs were evenly spaced along a circular orbit (radius 2 deg). Three colors were used in two identically-ordered triplets, e.g. red-green-cyan-red-green-cyan. The triplet of colors was chosen pseudorandomly on each trial. The blobs moved for three seconds. Observers fixated the center of the rotating ring and subsequently attempted to report the colors' relative order. In a second experiment, an outer (radius 4 deg) ring of blobs with three new colors, e.g. yellow-blue-fuchsia-yellow-blue-fuchsia, was added. Each blob in the inner ring was aligned with another in the outer ring and observers judged, for any color they chose of the inner ring, which color was aligned with it in the outer ring. In an identification control experiment, observers reported which colors were presented. To confirm the tracking limit, with all blobs set to the same color observers were cued to track one blob and at the end are tested on which blob it was. RESULTS. Observers could identify the colors (>90% correct) at rates over 2.5 rps. The limit on attentive tracking was much lower with average 75% threshold <1.5 rps. For the two experiments eliciting judgments of spatial relationships, 75% threshold rates were again 1.5 rps or lower and participants were near chance at rates for which the colors could easily be identified. Indeed, when viewing the display rotating at 2 rps, most observers are struck by their inability to grasp the relative location of any two colors, despite clear perception of the colors' identity. CONCLUSIONS. Coordinated individuation by attention may be necessary to extract most spatial relationships.
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