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.

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: Sep 26, 2014
• 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.
• Public URL: https://durham-repository.worktribe.com/output/1445115