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Matthew Davidson, Navindra Persaud, Brian Maniscalco, Dean Mobbs, Richard Passingham, Alan Cowey, Hakwan Lau; Awareness-related activity in prefrontal and parietal cortices reflects more than superior performance capacity: A blindsight case study. Journal of Vision 2010;10(7):897. doi: 10.1167/10.7.897.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Brain imaging studies on visual awareness have often reported activity in prefrontal and parietal cortices. One interpretation could be that such activity reflects the capacity to perform visual tasks, which is usually high when one is aware of the stimulus, and at near-chance-level when one is unaware. The opportunity to study a blindsight patient allowed us to test this interpretation, by creating performance-matched conditions with dramatic differences in subjectively reported levels of awareness. Patient GY has a damaged primary visual cortex in the left hemisphere (“blind”), with the right side being relatively intact (“normal). It is well-documented that he can perform forced-choice tasks better than chance in his “blind” visual field. Methods: We presented gratings of strong contrast to his “blind” field, and weak contrast to his “normal” field, such that performance in a spatial 2AFC task was matched between the two. We assessed the level of awareness by standard subjective report (“Seeing” vs “Guessing”), confidence rating, and post-decision wagering. All of these measures supported the conclusion that the level of awareness differed dramatically, even though performance capacity was matched between the “blind” field and “normal” field stimulations. Results: 1. Comparing “normal” field vs. “blind” field stimulations, we found robust activations in the prefrontal and parietal cortices. 2. Whereas accuracy in the “normal” field (correct vs. incorrect trials) was driven by activity in the occipital and temporal cortices (sometimes bilaterally), accuracy in the “blind” field was driven mainly by subcortical activity, with a clear lack of activation in the occipital cortex. Conclusions: 1. Activity in prefrontal and parietal cortices is likely to reflect the ability to monitor and report perceptual certainty appropriately, rather than just superior visual performance capacity. 2. Blindsight is supported by subcortical mechanisms, as previously suggested.
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