Abstract
Blindsight denotes unconscious residual visual capacities in the context of an inability to consciously recollect or identify visual information. It has been described for color and shape discrimination, movement or facial emotion recognition. The present study investigates a patient suffering from cortical blindness whilst maintaining select residual abilities in face detection. Our patient presented the capacity to distinguish between jumbled/normal faces, known/unknown faces or famous people’s categories although he failed to explicitly recognize or describe them. Conversely, performance was at chance level when asked to categorize non-facial stimuli. Our results provide clinical evidence for the notion that some aspects of facial processing can occur without perceptual awareness, possibly using direct tracts from the thalamus to associative visual cortex, bypassing the primary visual cortex.
Highlights
Patients with damage to the geniculocalcarine visual pathways may present cortical blindness
Patient A.M. suffered from lesions of the left primary visual cortex and the right optic tract leading to cortical blindness, except for a strong light source in the left hemifield
He failed to discriminate shapes and objects, showing no evidence of blindsight as it has been traditionally described (Cowey, 2010). He maintained some remarkable capacities for facial processing (Figure 3)
Summary
Patients with damage to the geniculocalcarine visual pathways may present cortical blindness. Some of them demonstrate the capacity to correctly ‘‘guess’’ visual characteristics during forced choice task, reflecting unconscious visual perception This residual visual ability without perceptual awareness is termed ‘‘blindsight’’ (Sanders et al, 1974; Weiskrantz et al, 1974; Stoerig and Cowey, 2007; Cowey, 2010) Visual pathways flowing directly from the retina to the superior colliculus (by passing the lateral geniculate nucleus (LGN)) or projections from the LGN to areas beyond striate cortex have been suggested to mediate blindsight behavior (Lamme, 2006; Stoerig and Cowey, 1997; Goebel et al, 2001; Tong, 2003; Stoerig and Cowey, 2007). These patients have maintained the ability to discriminate between different facial emotions (de Gelder et al, 1999; Hamm et al, 2003)
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