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Ceri T. Trevethan, Arash Sahraie, Lawrence Weiskrantz; When does a boy look like a gate? Form discrimination in blindsight?. Journal of Vision 2005;5(8):287. doi: https://doi.org/10.1167/5.8.287.
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© ARVO (1962-2015); The Authors (2016-present)
Background: DB, the first blindsight case to be tested extensively, has demonstrated the ability to detect and discriminate certain stimuli presented within his perimetrically blind field defect. Recent testing has revealed an improvement in DB's residual visual abilities. He is able to detect and discriminate visual stimuli that are considerably ‘less detectable’ than the optimal stimulus parameters often required to elicit blindsight (Sahraie et al 2003), and is now able to discriminate between certain shapes and make a ‘same/different’ judgement within his field defect (Trevethan et al, VSS 2004). Purpose: To investigate DB's ability to identify simple outline shapes, low-contrast line drawings and complex images (digital photographs) within his cortically blind field defect. Methods: Using a forced response paradigm, we investigated DB's ability to identify outline shapes (circle, oval, square, rectangle). DB was then tested on his ability to identify low-contrast (2%) line drawings of animals and modes of transport. Finally, DB was tested on his ability to spontaneously identify complex images (digital photographs) presented within his field defect. Results: In his field defect, DB demonstrated the ability to identify some simple outline shapes (choice of four shapes). DB was also able to identify some line drawings of animals and modes of transport (DB was told the category of stimuli before testing). Finally, DB demonstrated the ability to successfully identify some complex images within his field defect (given no indication of category). Conclusions: The ability to identify simple shapes and complex images within a cortically blind area of visual field has been demonstrated in DB. Analysis of DB's errors suggests that his performance cannot be explained on the basis of degraded normal vision. Results will be discussed in relation to the potential neuronal mediation of these abilities.
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