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Kenchi Hosokawa, Yutaka Nakajima, Takao Sato; Perceptual elasticity in stereokinetic effect. Journal of Vision 2007;7(9):841. doi: 10.1167/7.9.841.
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© ARVO (1962-2015); The Authors (2016-present)
In the stereokinetic effect, rotated nested figures yield cone- or pyramid-like 3D impressions. We found that similar displays consisted of pseudo-concentric squares (squares with slightly shifted centers) induced elastic 3D object impression. This elastic impression systematically changes as the displacements between centers of squares are varied. In this study, we examined the relationship between the elasticity and the amount of shift between centers to explore the source of the elasticity. The stimuli were pseudo-concentric 15 squares of different sizes (edge size = 1 to 15 deg, in 1 deg steps). The center of each square was placed along a small circle according the size order with a fixed angular shift. They were moved simultaneously at a fixed angular velocity while keeping centers on the circle and the orientation upright. The shift size was varied between 0 to 64 degs and subjects were asked whether they perceived rigid or elastic 3D object, or no 3D impression at all. The solid 3D impression was perceived when the angular shift was less than 4 degs, but elasticity emerged for larger shifts up to 40 degs. Beyond this limit, 3D impression was completely lost. The shape of the lines connecting vertices is straight with zero shift, but it became sinusoidal when a shift was added. The sinusoid moves as a traveling wave and its spatial frequency increases as the angular shift was increased. This sinusoidal motion is a measure of display's violation from rigidity and is the source of elasticity observed in the present display. This suggests that 3D recovery and elasticity perception are independent. However, the disappearance of 3D impression when the frequency of the sinusoid increased beyond certain limit suggests some interaction between the two systems.
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