Dissociations between perception and awareness in hemianopia

Issue title: Special Section: Low Vision: Rescue, Regeneration, Restoration and Rehabilitation

Guest editors: Andrea Antal and Bernhard Sabel

Article type: Research Article

Authors: Chokron, Sylvie^{b; *} | Dubourg, Lucas^{a; b} | Garric, Clémentine^c | Martinelli, Fiora^b | Perez, Céline^{a; b}

Affiliations: [a] Institut de Neuropsychologie, Neurovision, NeuroCognition, Fondation Ophtalmologique Adolphe de Rothschild, Paris, France | [b] Integrative Neuroscience and Cognition Center, CNRS, UMR 8242 et Université Paris-Descartes, Paris, France | [c] Laboratoire de Sciences Cognitives et Affectives, SCALab, CNRS UMR, Faculté de Médecine, Pôle Recherche et Université de Lille, Lille, France

Correspondence: [*] Corresponding author: Sylvie Chokron, Institut de Neuropsychologie, Neurovision, Neurocognition, Fondation Ophtalmologique Rothschild, 3 rue André Dubois, 75019 Paris, France. Tel.: +33 1 48036672; Fax: +33 1 48036551; E-mail: sylvie.chokron@gmail.com.

Abstract: The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby patients are blind to the contralesional visual field of each eye. Homonymous hemianopia has been studied in terms of its deleterious consequences on perceptual, cognitive and motor tasks as well as because it represents an interesting model of vision loss after a unilateral lesion of the occipital lobe. From a behavioral perspective, in addition to exhibiting a severe deficit in their contralesional visual field, HH patients can also exhibit dissociations between perception and awareness. Firstly, HH patients suffering from anosognosia may be unaware of their visual field defect. Secondly, HH patients can present with unconscious visual abilities in the blind hemifield, a phenomenon referred to as blindsight. Thirdly, recent reports demonstrate that HH patients can suffer from a subtle deficit in their ipsilesional visual field that they are unaware of, a condition called sightblindness (i.e. the reverse case of ‘blindsight’). Finally, HH patients may also exhibit visual hallucinations in their blind field; however, such patients are not systematically aware that their perceptions are unreal. In this review, we provide an overview of the visual-field losses in HH patients after a left or right unilateral occipital lesion. Furthermore, we explore the implications of these four phenomena for models of visual processing and rehabilitation of visual field defects in HH patients. Finally, in contrast to the traditional view that HH is solely a visual-field defect, we discuss why this deficit is an interesting model for studying the dissociation between perception and awareness.

Keywords: Homonymous hemianopia, blindsight, anosognosia, hallucinations, awareness, occipital lobe

DOI: 10.3233/RNN-190951

Journal: Restorative Neurology and Neuroscience, vol. 38, no. 3, pp. 189-201, 2020