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Residual vision in a scotoma: implications for blindsight
R Fendrich1, C M Wessinger, M S Gazzaniga
1Center for Neuroscience, University of California, Davis 95616.
Science (New York, N.Y.)
|November 27, 1992
Summary
Blindsight may result from residual function in the primary visual pathway, not just secondary pathways. Researchers found a small island of vision in a hemianopic patient
Area of Science:
- Neuroscience
- Visual Perception
- Neuro-ophthalmology
Background:
- Blindsight, the ability to perceive visual stimuli without conscious awareness, is typically attributed to the secondary (retinotectal) visual pathway.
- An alternative hypothesis suggests blindsight may arise from residual function within the primary (geniculostriate) visual pathway.
Observation:
- Using an image stabilizer for precise stimulus presentation, researchers conducted detailed visual field mapping on a patient with hemianopia.
- Conventional perimetry failed to detect a small, isolated area of residual vision within the patient's visual field defect (scotoma).
Findings:
- This previously undetected 1-degree island of vision allowed the patient to detect and discriminate stimuli.
- Despite successful detection, the patient reported no conscious visual experience, a hallmark of blindsight.
Implications:
- The existence of this visual island suggests a corresponding localized area of functioning cortical tissue within the patient's brain lesion.
- This finding supports the role of residual primary visual pathway function in blindsight and suggests similar cortical islands may mediate other cases.