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Johannes Zanker, Stefano Targher, Szonya Durant; A new Barbers Pole configuration to study the integration of local motion information. Journal of Vision 2007;7(9):979. doi: 10.1167/7.9.979.
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The Barbers Pole illusion is an instructive demonstration of the mechanisms in the visual system that integrate local motion information. Long-range interactions between ambiguous and unambiguous motion components have been investigated in a cross shaped arrangement of two elongated apertures (Castet et al., Spatial Vision 12, 1999). Here we present experiments using a lattice configuration of several horizontally and vertically extended apertures (‘slits’) behind which a diagonal grating is moving at constant speed. As expected from the Barbers Pole illusion, observers perceive horizontal motion in the horizontal slits and vertical motion in the vertical slits. At the intersections between the perpendicular slits the ambiguous information is resolved as a bistable motion percept — observers report an alternation between horizontal and vertical motion, which interestingly appears to happen in synchrony for all intersections. We used small occluders to extend either the horizontal or vertical aperture outlines across one of the intersections, and asked participants to report the dominating motion direction at this intersection, or at neighbouring intersections which had no occluders. These experiments show that bistable percepts disappear not only in the intersection that has been disambiguated but also in neighbouring ones, for a wide range of stimulus parameters. This bias towards the disambiguated motion direction drops off with increasing distance from the occluded intersection, allowing us to assess the relative strength of long-range interactions between local motion signals that play a crucial role in the Barbers Pole illusion.
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