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Conscious visual abilities in a patient with early bilateral occipital damage

Published online by Cambridge University Press:  16 October 2003

Deborah Giaschi
Affiliation:
Department of Ophthalmology, University of British Columbia (UBC), Vancouver, British Columbia, Canada.
James E Jan
Affiliation:
Department of Pediatrics, UBC, Canada.
Bruce Bjornson
Affiliation:
Department of Pediatrics, UBC, Canada.
Simon Au Young
Affiliation:
Department of Pediatrics, British Columbia's Children's Hospital, Canada.
Matthew Tata
Affiliation:
Department of Psychology, UBC , Canada.
Christopher J Lyons
Affiliation:
Department of Ophthalmology, University of British Columbia (UBC), Vancouver, British Columbia, Canada.
William V Good
Affiliation:
Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA.
Peter KH Wong
Affiliation:
Department of Pediatrics, UBC, Canada.
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Abstract

A 21-year-old male presented with occipital lobes that were extensively damaged by bilateral infarcts present at birth. The absence of the striate cortex was confirmed with anatomic and functional MRI and high-resolution EEG. His cortical visual impairment was severe, but he retained a remarkable ability to see fast-moving stimuli. Horizontal optokinetic nystagmus could be elicited from either eye. Resolution acuity was close to normal providing the patient was allowed to move his head and eyes. The direction of motion in random-dot patterns could be discriminated with perfect accuracy at speeds above 2 deg/s, and the patient reported that he could ‘see’ the motion at fast but not at slow speeds. This conscious residual vision for motion is known as Riddoch's phenomenon, but it has never been reported in the complete absence of the striate cortex. Functional neuroimaging revealed activation that was outside the motion-responsive regions of the extrastriate cortex. This case demonstrates remarkable plasticity in the human visual system and may have implications for understanding the functional organization of the motion pathways.

Type
Case Report
Copyright
© 2003 Mac Keith Press

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