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Paul Dassonville, Tim Sanders, Brad Capp; The rod-and-frame and simultaneous tilt illusions: Perception, action and the two-wrongs hypothesis. Journal of Vision 2009;9(8):845. doi: 10.1167/9.8.845.
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Several studies have demonstrated a dissociation of the effects of illusion on perception and action, with perception generally reported to be susceptible to illusions, while actions seem immune. These findings have been interpreted as supporting Milner & Goodale's hypothesis for the existence of separate visual processing streams for perception and action. However, work from our lab (Dassonville & Bala, PLoS Biol 2004) and that of Matin (Li & Matin, Vis Res 2005) has suggested that this type of behavioral dissociation will occur for any illusion that is caused by a distortion of the observer's egocentric reference frame, without providing evidence for the existence of separate visual representations for perception and action. According to this Two-wrongs hypothesis, movements aimed at illusory targets will be accurate if they are guided within the same distorted reference frame used for target encoding, since the error of motor guidance will cancel with the error of encoding (hence, for actions, “two wrongs do make a right”). Here, we further test the Two-wrongs hypothesis, by examining two illusions for which the hypothesis makes very different predictions: the rod-and-frame illusion (which affects perception but not actions, Dyde & Milner, Exp Brain Res 2002) and the simultaneous tilt illusion (which affects perception and actions equally, Dyde & Milner 2002). As predicted, the mechanism that drives the rod-and-frame effect is a distortion of the observer's egocentric reference frame, while the simultaneous tilt illusion is caused by local interactions between stimulus elements within an undistorted reference frame. These results provide evidence for a class of illusions that lead to dissociations of perception and action through distortions of the observer's spatial reference frame, rather than through the actions of separate visual processing streams.
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