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Andrew Dunn, Peter Thompson; Different illusory effects of the Judd illusion for perception and action after a temporal delay. Journal of Vision 2002;2(7):55. doi: 10.1167/2.7.55.
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Milner & Goodale (1995) have provided a useful, if controversial model for investigating the contribution of visual information in motor action. We have explored the effects of the Judd Illusion upon perception (position matching) and motor action (pointing), in relation to this model. In the motor task participants made ballistic pointing responses towards the end point (left/right) or mid point (marked/unmarked) of a Judd illusion where as in the perceptual task participants made judgements about the location of a line relative to these positions. When these tasks were carried out immediately after brief presentation of the stimulus, illusory effects were observed for both pointing and matching at the endpoints and unmarked midpoints. This at first appears to contradict the Milner & Goodale (1995) two streams hypothesis, however when a temporal delay was introduced between stimulus presentation and response a different pattern of effects emerged. For pointing, error increased at the end points but went in a direction opposite to the illusion for the marked mid point. For perceptual matching the error increase in size at both the marked and unmarked midpoint but not at the end point. We interpret these results as evidence for comparison process using separate visual motor and separate visual perceptual representations, in line with the Milner & Goodale's (1995) model.
MilnerA. D.GoodaleM. A.(1995). The visual brain in action. Oxford University Press: Oxford.
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