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Stuart Anstis; Perceptual grouping of ambiguous motion. Journal of Vision 2010;10(7):848. doi: 10.1167/10.7.848.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction. What are the rules of common fate? How are spots that move in different directions grouped perceptually? Method. A pair of spots, separated by 2°, rotate about their common centre at 1 rps. Four such pairs spin in synchrony at the corners of an imaginary square of side 8°. Results. On first viewing, observers report four spinning pairs (Local motion), but after 5–20s the percept suddenly changes to two overlapping 8° squares circling around (Global motion). Thereafter, global motion tends to predominate. Factors that increase local motion include: Gazing straight at a spinner. Proximity – putting the two spots in a spinner closer together. Orientation – replacing the spots within a spinner by two radial or tangential dashes (as if painted on an invisible disk). Luminance – making each spot-pair a different grey. Increasing the number of spots in each spinner from 2 up to 3 or 4. Factors that increase global motion include: Viewing spinners in peripheral vision. Moving the two spots in a spinner further apart. Orientation – replacing the spots with two floating lines that remain horizontal (or vertical) as they spin. Luminance polarity – on a grey surround, four spots defining an 8° square (one spot from each pair) are black, the remaining spots are white. Increasing the number of spinners from 4 to 8. Conclusions. It is a more parsimonious perceptual hypothesis to group the data from the motion array into only two objects (squares) moving globally, rather than into four objects (spinners) moving locally.
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