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Chris Dodds, Liana Machado, Robert Rafal, Tony Ro; A temporal /nasal asymmetry for blindsight: Evidence for extrageniculate mediation.. Journal of Vision 2002;2(7):23. doi: https://doi.org/10.1167/2.7.23.
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© ARVO (1962-2015); The Authors (2016-present)
Some patients with hemianopia due to striate cortex lesions show above chance ability in reporting visual stimuli presented in the blind visual field, a phenomenon commonly known as blindsight. Here we report a patient, MP, with a dense right hemianopia whose blindsight shows a temporal/nasal asymmetry. MP was tested in a 2-alternative forced-choice localisation task, with either the right eye or the left eye patched in separate blocks. On each trial a 2 degree black circle appeared on a light-grey background in the blind hemifield, either 10 degrees (‘near’) or 20 degrees (‘far’) from fixation (or no stimulus was presented on 12.5% of trials), and MP reported ‘near’ or ‘far’. Eye position was monitored throughout testing to ensure central fixation. When targets appeared in the contralesional temporal hemifield, MP's localisation performance was extremely accurate. In contrast, MP performed at chance with targets in the contralesional nasal hemifield. The temporal/nasal asymmetry is consistent with blindsight in MP's hemianopic field being mediated by a subcortical, extrageniculate route.
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