Minini L, Wattam-Bell J, 2005, "Contour interpolation in the dorsal visual system: Accurate grasping with Kanizsa squares" Perception 34 ECVP Abstract Supplement
Contour interpolation in the dorsal visual system: Accurate grasping with Kanizsa squares
L Minini, J Wattam-Bell
In agreement with the two-visual-systems hypothesis (Goodale and Milner, 1992 Trends in Neurosciences 15 20 - 25), several investigators have found that a number of visual illusions do affect perception to a greater extent than action. These findings are in agreement with the proposal that the ventral and dorsal visual systems independently mediate visual processing for perception and object-directed action, respectively, and that the latter processes the absolute, retinally specified, metrics of the target. More recently Dyde and Milner (2002 Experimental Brain Research 144 518 - 527) proposed that visual illusions that are largely processed in areas that precede the anatomical chiasm between the two systems should affect both perception and action. We tested this claim by measuring whether the scaling of grip aperture in grasps with Kanizsa illusory contours, a phenomenon thought to be modulated by early visual cortex (Peterhans and von der Heydt, 1989 Journal of Neuroscience 9 1749 - 1763), is accurate. A comparison of the maximum grip apertures from grasps with 3-D, 2-D-luminance-defined, 2-D-Kanizsa, and 2-D-control stimuli revealed significantly larger apertures for the 3-D condition, but, crucially, no differences between any of the other conditions. Differences between grasps with the 3-D and 2-D stimuli could be accounted for by the additional haptic feedback available from 3-D targets. More notably, however, grasps with the Kanizsa or control stimuli were as accurate as with the luminance-defined stimuli, clearly suggesting that information about the interpolated contours was available to the dorsal pathway. These results are in agreement with the claim that the dorsal visual system does not process only the retinally specified properties of the target, but that it can use other signals when these are generated in early visual cortex.
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