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B. Pinna, M. Boi; The rotating circle illusion. Journal of Vision 2006;6(6):552. doi: 10.1167/6.6.552.
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A novel motion illusion is shown consisting of a white circle moving across or behind black parallel lines on a grey background. When the gaze is kept on the centre of the circle, the circle appears to rotate even if it is, in fact, translating. The apparent motion can only be perceived in peripheral vision.
Phenomenology of the illusion: (i) the rotation persists when then circle and/or the background are composed of textured patterns (e.g. irregularly scattered dot) or by making the circle more and more similar to a square or an ellipse; (ii) the effect is increased when the circle is in front of the background, transparent, illusory or has the same contrast as the background elements whereas it is reduced when the circle is filled or by moving the textured background while keeping the circle stationary; (iii) attentive focusing on the bottom or on the top part of the circle induces a rotation respectively synergistic or opposite to the translational movement; (iv) the rotation is perceived in the entire circle even though the background intersects only a portion of it.
The illusion is related to the one reported by Cormack, Blake and Hiris (1992) but, unlike this one, here the shape influences the very type of perceived motion depending on: the motion of the intersections between circle and background elements, a figural integration of the motion vectors along the moving shape, a long range filling in process of the induced rotation spreading across regions where no intersections occur.
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