What Accounts for Blindsight?

Paper Summary:

This paper looks at the problem of blindsight, defined as the ability to process visual information without conscious awareness. The paper presents two theories as to the cause and provides results of various studies on the topic.

From the Paper:

"Blindsight is defined as the residual visual ability of patients with damage to the primary visual cortex of the brain to react reliably to the emotional valence of stimuli presented to their blind visual fields and whose presence and properties they are unable to report. In short, it is the ability to process visual information without conscious awareness. Although, neuro-anatomical explanation of this phenomenon is still not fully understood."
"It has been debated that blindsight can be explained by partial sparing of primary visual cortex, with sufficient preservation of cortical processing for stimuli versus functional integrity of this subcortical visual pathway. Cortical preservation says that there are "islands" of spared cortex that accounts for the ability of the patient to still "see" despite being unconscious to the surrounding world. But, despite the explanations, cortical preservation theory has been ruled out based on behavioral and neuroimaging findings. This is because only little number of patients has sparing of the cortical tissue. But it was also found out that most of the patients with occipital cortex damage, and this includes those with preservation of cortex, have intact superior colliculi. On the other hand, visual information transmitted through the retinotectal pathway is projected to extra striate visual cortex. This is said to be sufficient enough to drive visually guided behavior without awareness."

Sample of Sources Used:

• Jacob Jolij and Victor A. F. Lamme, TMS induced affective blindsight reverts to affective blindness when stimulus visibility is increased.
• Beatrice de Gelder and Marco Tamietto, Affective Blindness. Scholarpedia, 2(10):3555, 2007.
• Tony Ro and Robert Rafal. Visual restoration in cortical blindness: Insights from natural and TMS-induced blindsight. NEUROPSYCHOLOGICAL REHABILITATION 16 (4), 377-396, 2006.
• Goodale, M. A., & Milner, A. D. Separate visual pathways for perception and action. Trends in Neurosciences, 15, 20-25, 1992.
• Blythe, I. M., Kennard, C., & Ruddock, K. H. Residual vision in patients with retrogeniculate lesions of the visual pathways. Brain, 110(Pt 4), 887-905, 1987.

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