Blindsight: the role of feedforward and feedback corticocortical connections

When human subjects suffer from a lesion to the primary visual cortex, they lose all visual percepts in the region of space that corresponds to the si te of the lesion. However, they are still capable of responding to stimuli in this region when asked to 'guess' or to execute forced-choice motor comm ands related to these stimuli. This phenomenon, termed blindsight, is still only partly understood. Here, the possible roles of Feedforward and feedba ck corticocortical connections in the visual brain in the understanding of blindsight are reviewed. What emerges is substantial evidence in favor of t he theory that unconscious visuo-motor transformations, as in blindsight, m ay be executed in an entirely feedforward processing cycle, while visual aw areness is critically dependent on feedback connections to the primary visu al cortex. (C) 2001 Elsevier Science B.V. All rights reserved.