Affective blindsight in the intact brain: neural interhemispheric summation for unseen fearful expressions.

The emotional valence of facial expressions can be reliably discriminated even in the absence of conscious visual experience by patients with lesions to the primary visual cortex (affective blindsight). Prior studies in one such patient (GY) also showed that this non-conscious perception can influence conscious recognition of normally seen emotional faces. Here we report a similar online interaction across hemispheres between conscious and non-conscious perception of emotions in normal observers. Fearful and happy facial expressions were presented either unilaterally (to the left or right visual field) or simultaneously to both visual fields. In bilateral displays, conscious perception of one face in a pair was prevented by backward masking after 20 ms, while the opposite expression remained normally visible. The results showed a bidirectional influence of non-conscious fear processing over conscious recognition of happy as well as fearful expressions. Consciously perceived fearful faces were more readily recognized when they were paired with invisible emotionally congruent fearful expressions in the opposite field, as compared to the single presentation of the same unmasked faces. On the other hand, recognition of unmasked happy faces was delayed by the simultaneous presence of a masked fearful face. No such effect was reported for masked happy expressions. These findings show that non-conscious processing of fear may modulate ongoing conscious evaluation of facial expressions via neural interhemispheric summation even in the intact brain.