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Daisuke Hayashi, Masahiko Terao, Lin Cai, Takayuki Osugi, Ikuya Murakami; Diagonal Stretch Illusion: the distance between dots appearing longer when surrounded by circles. Journal of Vision 2015;15(12):467. doi: https://doi.org/10.1167/15.12.467.
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© ARVO (1962-2015); The Authors (2016-present)
We found a new illusion that makes the distance between two small dots appear longer. When two of the four dots comprising a square shape are surrounded by thick circles, the diagonal distance between the two dots (length of the “test” diagonal) subjectively becomes longer than the distance between the dots without surrounding circles (length of the “comparison” diagonal). We named this phenomenon ‘Diagonal Stretch Illusion’. Several important characteristics of this phenomenon are listed as follows. (1) The degree of this illusion is higher when the test diagonal is horizontal rather than vertical, opposite to the prediction from the vertical-horizontal illusion. (2) Stimulus duration for 100 ms is sufficient. (3) This illusion is observed in both foveal and peripheral vision. (4) As the surrounding circles become thinner and/or smaller, the illusion becomes weaker. In contrast, a strong illusion is obtained from dots superimposed upon large disks rather than surrounding circles. (5) The longer absolute distance between dots makes the illusion weaker. (6) The illusion is robust even when surrounding circles are contrast-defined or when circles and dots are color-defined. (7) To produce this illusion, surrounding stimuli can be circles, squares, or even illusory-contour squares. The last observation rules out accounts in terms of depth perception because dots on the illusory-contour squares should appear nearer than dots on the background, and Emmert’s law dictates that nearer objects should appear closer to each other. (8) After adaptation to a subjectively stretched shape, an isotropic shape appears to be stretched along an orthogonal axis. From these observations, we propose that the visual system possesses some distance estimation mechanism that produces a systematic bias in the presence of surrounding stimulus patterns in addition to localized points of interest, and that such a mechanism is located early enough to be adaptable following prolonged observation.
Meeting abstract presented at VSS 2015
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