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P. Thompson, A. Dunn; Pointing at the Judd Illusion. Journal of Vision 2001;1(3):255. doi: https://doi.org/10.1167/1.3.255.
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An investigation was carried out examining the susceptibility of open-loop pointing to the Judd illusion.. 14 Ss were required to reach and touch left/right and mid points (marked or unmarked) of a left /right facing Judd illusion and a control figure. Stimuli were presented centrally, on a touch screen monitor, with stimuli replaced by a pattern mask as soon as a pointing movement was initiated. Analysis of the data revealed no effect when reaching towards either the marked centre of a Judd illusion or anywhere on the marked or unmarked control. A significant effect of the illusion was found when pointing to the end points and the unmarked centre of the Judd figure. These results raise interesting questions about the effects of visual illusions upon object oriented action, since they appear to contrast with previous experiments by Post and Welch (1996) who found illusory effects only when striking (open loop) the unmarked centre of a Judd figure, not its end points). The implications of these results for Milner and Goodale's (1995) claim that the motor system should remain unaffected by visual illusions due to egocentric processing in the dorsal stream will be discussed.
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