Conscious and veridical motion perception in a human hemianope
Following lesions to the primary visual cortex, some patients maintain visual capacities within areas of the visual field in which they are defined as clinically blind by static field perimetry. Blindsight describes the ability to discriminate visual stimuli in the absence of awareness of the stimuli in such patients. Some patients exhibit blindsight, but others are aware of the stimuli with which they are presented, a response mode that has been referred to as residual vision. The two response modes are of great interest as they are capable of providing us with information concerning the conscious and unconscious processing of visual signals in humans. However, determining consciousness in these patients is a difficult task and relies on the patient assessing and then reporting on his awareness. In this paper, an experiment is described which is capable of demonstrating conscious visual processing of motion under conditions where the observer is not required to assess his level of awareness. In applying this technique to a human hemianope, GY, it is demonstrated that GY has veridical and conscious perception of visual motion presented to his blind hemifield. Although previously reported, this result can be derived without any reference to GY's commentary on his blind field perception.
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Document Type: Research Article
Affiliations: Physics Department (Biophysics), Blackett Laboratory, Imperial College, London SW7 2BZ, U.K.
Publication date: May 1, 1999