Congenital or acquired damage to the visual processing areas of the brain is often associated with a loss of vision. Despite sustaining damage to these brain areas, some people retain an unconscious ability to respond to visual stimuli — and ability termed blindsight. Although these people are not consciously aware of visual stimuli, they are in many instances able to direct their eyes towards target items and to discriminate the orientation and direction of movement presented in their area of blindness.
Studies examining blindsight have found that those who acquire damage early in life retain more visual ability than those who acquire brain damage in adolescence or adulthood. The authors of the current article, published in the journal Cortex, investigated the visual ability and neural responses of children who had acquired damage to the optic radiation — a collection of axons which carry visual information to the visual cortex — neonatally or in adolescence.
The children completed a cross-hemispheric alignment task and a task testing for sensitivity to motion and orientation. In the cross-hemispheric alignment task, the children were shown two gratings, one of which was purposefully placed within the child’s scotoma (i.e., area of visual blindness). The children were asked to indicate which grating was placed higher on the visual display.
In the motion and orientation task, children were shown a single grating displayed within their intact visual field or within their scotoma. The grating either moved from left to right, or was placed at an inclined angle, and the children had to indicate the direction of the motion or the orientation of the grating. Two of the children who had congenital brain damage also underwent functional Magnetic Resonance Imaging (fMRI) to determine neurological function during the processing of visual stimuli.
All of the children with congenital brain damage displayed unconscious visual perception on all three of the visual tasks (alignment, motion, and orientation), while children who had acquired brain damage in adolescence did not. fMRI revealed that the intact hemisphere of the brain responded to visual stimuli presented in the blind hemifield of children with congenital brain damage.
These findings suggest that residual vision in people with blindsight may be due to massive reorganization of their visual system. The brains of very young children are highly plastic allowing those who acquire brain damage early in life a better chance of compensating for the damaged structures and regaining lost functioning.
Tinelli F, Cicchini GM, Arrighi R, Tosetti M, Cioni G, & Morrone MC (2013). Blindsight in children with congenital and acquired cerebral lesions. Cortex; a journal devoted to the study of the nervous system and behavior, 49 (6), 1636-47 PMID: 22939919