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Michael McCloskey, Emma Gregory; Persistence of Visual Mislocalizations across Eye Movements in a Case of Impaired Visual Location Perception: Implications for Visual Updating and Visual Awareness. Journal of Vision 2010;10(7):561. doi: 10.1167/10.7.561.
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© ARVO (1962-2015); The Authors (2016-present)
AH, a young woman with a developmental deficit in perceiving the location of visual stimuli, makes left-right and up-down reflection errors in a variety of tasks. For example, she may reach, point, or saccade to the right for an object on her left, or verbally report that a stimulus is at the bottom of a display screen when in fact it is at the top. Extensive testing revealed that AH's impairment is a selective visual deficit, and that her errors arise not in early vision, but rather at a higher level of visual representation. Remarkably, AH's misperceptions of location often persist across eye movements. When she erroneously perceives an object to be on her left while looking straight ahead, and saccades leftward in an effort to fixate the object, she may then report that she is looking at the object, despite the fact that the eye movement shifted the target further into the visual periphery. We argue that these persisting visual mislocalization errors shed light on trans-saccadic processing of location information in the normal visual system. When the eyes move, a new high-level representation of an object's location could be constructed by updating the initial high-level representation to account for the eye movement (using corollary discharge information), and/or by computing a high-level representation de novo from post-saccadic low-level visual representations. From results of several tasks probing AH's persisting visual mislocalizations, we argue that de novo computation of new high-level representations from new low-level representations is not automatic following an eye movement; as long as low-level representations imply that the visual scene has not changed, new high-level representations may be generated by updating alone. Finally, with respect to visual awareness, we argue that AH's location misperceptions imply that awareness is mediated by high- and not low-level visual representations.
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