Vertical gaze angle as a distance cue for programming reaching: insights from visual form agnosia II (of III) |
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Authors: | Mon-Williams M McIntosh R D Milner A D |
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Institution: | (1) School of Psychology, University of St Andrews, St Andrews, Fife KY16 9JU, UK,;(2) Department of Psychology, University of Durham, Science Laboratories, South Road, Durham DH1 3LE, UK, |
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Abstract: | It has been shown that a patient with visual form agnosia (DF) relies predominantly on vergence information when gauging
target distance in an open-loop pointing task. This finding suggested that the programming of prehension might be severely
disrupted if DF viewed target objects through ophthalmic prisms. An initial experiment showed that this prediction was not
upheld; DF was able to programme reasonably accurate movements to objects located on a tabletop despite large changes in vergence
angle. A second experiment, however, showed that placing the target objects at eye height whilst manipulating vergence angle
caused gross disruption to prehension, with DF mis-programming the reach component in a predictable manner. Notably, the evidence
for DF's reliance on vergence distance information was obtained in a task where the targets were viewed at eye height. These
experiments indicate that DF uses vertical gaze angle to gauge target distance in normal prehension and suggest that this
extra-retinal cue may be a useful source of distance information for the human nervous system, especially where pictorial
cues are impoverished.
Electronic Publication |
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Keywords: | Prehension Binocular Vergence Distance perception Human |
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