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Patient DF's visual brain in action : visual feedforward control in patient with visual form agnosia

Whitwell, R.L.; Milner, A.D.; Cavina-Pratesi, C.; Barat, M.; Goodale, M.A.

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Authors

R.L. Whitwell

A.D. Milner

C. Cavina-Pratesi

M. Barat

M.A. Goodale



Abstract

Patient DF, who developed visual form agnosia following ventral-stream damage, is unable to discriminate the width of objects, performing at chance, for example, when asked to open her thumb and forefinger a matching amount. Remarkably, however, DF adjusts her hand aperture to accommodate the width of objects when reaching out to pick them up (grip scaling). While this spared ability to grasp objects is presumed to be mediated by visuomotor modules in her relatively intact dorsal stream, it is possible that it may rely abnormally on online visual or haptic feedback. We report here that DF’s grip scaling remained intact when her vision was completely suppressed during grasp movements, and it still dissociated sharply from her poor perceptual estimates of target size. We then tested whether providing trial-by-trial haptic feedback after making such perceptual estimates might improve DF’s performance, but found that they remained significantly impaired. In a final experiment, we re-examined whether DF’s grip scaling depends on receiving veridical haptic feedback during grasping. In one condition, the haptic feedback was identical to the visual targets, while in a second, the feedback was of a constant intermediate width while the visual target varied trial by trial. Despite such false feedback, DF still scaled her grip aperture to the visual widths of the target blocks, showing only normal adaptation to the false haptically-experienced width. Taken together, these results strengthen the view that DF’s spared grasping relies on a normal mode of dorsal-stream functioning, based chiefly on visual feedforward processing.

Citation

Whitwell, R., Milner, A., Cavina-Pratesi, C., Barat, M., & Goodale, M. (2015). Patient DF's visual brain in action : visual feedforward control in patient with visual form agnosia. Vision Research, 110(Part B), 265-276. https://doi.org/10.1016/j.visres.2014.08.016

Journal Article Type Article
Acceptance Date Aug 21, 2014
Online Publication Date Sep 6, 2014
Publication Date May 1, 2015
Deposit Date Sep 24, 2014
Publicly Available Date Mar 28, 2024
Journal Vision Research
Print ISSN 0042-6989
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 110
Issue Part B
Pages 265-276
DOI https://doi.org/10.1016/j.visres.2014.08.016
Keywords Two visual systems hypothesis, Visual form agnosia, Patient DF, Grasping, Feedforward vs. feedback visuomotor control, Perception–action dissociation, Visual feedback, Haptic feedback, Tactile feedback, Motor adaptation.

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Copyright Statement
NOTICE: this is the author’s version of a work that was accepted for publication in Vision Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Vision Research, 110, Part B, May 2015, 10.1016/j.visres.2014.08.016.





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