Conscious visual abilities in a patient with early bilateral occipital damage.
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.
Department of Ophthalmology, University of British Columbia (UBC), Vancouver, Canada. giaschi@interchange.ubc.ca
Deborah
D
Giaschi
James E
JE
Jan
Bruce
B
Bjornson
Simon Au
SA
Young
Matthew
M
Tata
Christopher J
CJ
Lyons
William V
WV
Good
Peter K H
PK
Wong
D000328:Adult; D019575:Blindness, Cortical / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology; D002544:Cerebral Infarction / Q000150:complications* / Q000209:etiology* / Q000473:pathology; D003243:Consciousness / Q000502:physiology*; D003342:Corpus Striatum / Q000002:abnormalities*; D004569:Electroencephalography; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D007744:Obstetric Labor Complications; D009778:Occipital Lobe / Q000098:blood supply* / Q000473:pathology*; D011247:Pregnancy; D012438:Saccades / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology; D014794:Visual Fields / Q000502:physiology