title: The Pointing Errors in Optic Ataxia Reveal the Role of "Peripheral Magnification" of the PPC.
abstract: Interaction with visual objects in the environment requires an accurate correspondence between visual space and its internal representation within the brain. Many clinical conditions involve some impairment in visuo-motor control and the errors created by the lesion of a specific brain region are neither random nor uninformative. Modern approaches to studying the neuropsychology of action require powerful data-driven analyses and error modeling in order to understand the function of the lesioned areas. In the present paper we carried out mixed-effect analyses of the pointing errors of seven optic ataxia patients and seven control subjects. We found that a small parameter set is sufficient to explain the pointing errors produced by unilateral optic ataxia patients. In particular, the extremely stereotypical errors made when pointing toward the contralesional visual field can be fitted by mathematical models similar to those used to model central magnification in cortical or sub-cortical structure(s). Our interpretation is that visual areas that contain this footprint of central magnification guide pointing movements when the posterior parietal cortex (PPC) is damaged and that the functional role of the PPC is to actively compensate for the under-representation of peripheral vision that accompanies central magnification. Optic ataxia misreaching reveals what would be hand movement accuracy and precision if the human motor system did not include elaborated corrective processes for reaching and grasping to non-foveated targets.
authors: ImpAct Team, Lyon Neuroscience Research Center CRNL, INSERM U1028, CNRS UMR5292 and University Claude Bernard Lyon I Villeurbanne, France.
authors: Philippe
authors: P
authors: Vindras
authors: Department of Experimental Psychology, University of Oxford Oxford, UK.
authors: Annabelle
authors: A
authors: Blangero
authors: Department of Occupational Therapy, School of Health Sciences, Sapporo Medical University Sapporo, Japan.
authors: Hisaaki
authors: H
authors: Ota
authors: ImpAct Team, Lyon Neuroscience Research Center CRNL, INSERM U1028, CNRS UMR5292 and University Claude Bernard Lyon I Villeurbanne, France.
authors: Karen T
authors: KT
authors: Reilly
authors: ImpAct Team, Lyon Neuroscience Research Center CRNL, INSERM U1028, CNRS UMR5292 and University Claude Bernard Lyon I Villeurbanne, France.
authors: Yves
authors: Y
authors: Rossetti
authors: ImpAct Team, Lyon Neuroscience Research Center CRNL, INSERM U1028, CNRS UMR5292 and University Claude Bernard Lyon I Villeurbanne, France.
authors: Laure
authors: L
authors: Pisella
keywords: mathematical modeling; models; optic ataxia; peripheral vision; posterior parietal cortex; theoretical; visual central magnification; visuo-motor control