Conscious visual perceptual awareness vs. non-conscious visual spatial localisation examined with normal subjects using possible analogues of blindsight and neglect

Localisation of unseen stimuli was produced with short-duration pattern-masked tachistoscopically presented targets in each of three studies with normal subjects (P<0.001). Conscious spatial attention did not influence sensitivity for this “blindsight” effect but did affect the criterion, according to a signal detection theory analysis. Unawareness of stimuli in an unattended visual field was also produced in each study (P<0.001). Conscious spatial attention decreased awareness sensitivity and increased criterion for unattended targets, leading to this “neglect” effect. As with clinical patients, greater left than right side neglect was found. This neglect asymmetry resulted from lower awareness sensitivity on the left. The blindsight and neglect effects were negatively correlated, consistent with the view that both effects reflect the function of the same visual localisation system. This system may operate without awareness, be largely unaffected by conscious attention, provide blindsight localisation when intact, and lead to neglect when damaged.