Blindsight - Research

Research

Lawrence Weiskrantz and colleagues showed in the early 1970s that if forced to guess about whether a stimulus is present in their blind field, some observers do better than chance. This ability to detect stimuli that the observer is not conscious of can extend to discrimination of the type of stimulus (for example, whether an 'X' or 'O' has been presented in the blind field).

Electrophysiological evidence from the late 1970s (de Monasterio, 1978; Marrocco & Li, 1977; Schiller & Malpeli, 1977) has shown that there no direct retinal input from S-cones to the superior colliculus, implying that the perception of color information should be impaired. However, recent evidence point to a pathway from S-cones to the superior colliculus, opposing de Monasterio’s previous research and supporting the idea that some chromatic processing mechanisms are intact in blindsight.

Marco Tamietto & Beatrice de Gelder performed experiments linking emotion detection and blindsight. Patients shown images on their blind side of people expressing emotions correctly guessed the emotion most of the time. The movement of facial muscles used in smiling and frowning were measured and reacted in ways that matched the kind of emotion in the unseen image. Therefore, the emotions were recognized without involving conscious sight.

A recent study found that a young woman with a unilateral lesions of area V1 could scale her grasping movement as she reached out to pick up objects of different sizes placed in her blind field, even though she could not report the sizes of the objects. Similarly, another patient with unilateral lesion of area V1 could avoid obstacles placed in his blind field when he reached toward a target that was visible in his intact visual field. Even though he avoided the obstacles, he never reported seeing them.