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Monika Harvey, Robert McIntosh, Stephen Butler, Larissa Szymanek, Stephanie Rossit; On-line reaching to perturbed targets in visual form agnosia (patient DF). Journal of Vision 2009;9(8):1164. doi: 10.1167/9.8.1164.
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According to Milner and Goodale's model (2006) areas in the ventral visual stream mediate visual perception whereas regions in the dorsal visual stream are closely involved with the visual control of action. Indeed the demonstration of an ‘autopilot deficit’ in optic ataxia (the inability to update a movement after a target jump as a result of bilateral occipito-parietal damage) has been presumed to reflect damage to the dorsal visual pathway. So far, this has only been shown as a single dissociation, with the strong prediction that the ability to make automatic corrections should be preserved if the dorsal stream is spared, for example in the visual form agnosic patient DF.
Here we investigated whether DF, when compared to age-matched controls, could rapidly adjust or interrupt her ongoing reach in response to a target jump. We found that DF successfully corrected her reaches towards the location shifts. Moreover in the stop condition, unlike optic ataxia patients, she performed involuntary corrections towards the target shifts in spite of being instructed to interrupt her reach.
Our data thus provide evidence for the expected double dissociation, further supporting localisation of the ‘autopilot’ to the dorsal visual pathway.
Milner, A.D. and Goodale, M.A. (2006). The visual brain in action. OUP.
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