Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia

Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1-8]. Littl e is known on the possibility that unconscious vision is influenced by visu al cues that have access to consciousness [9]. Here we report a 'blind' let ter discrimination induced through a semantic interaction with conscious co lor processing in a patient who is agnosic for visual shapes, but has norma l color vision and visual imagery. In seeing the initial letters of color n ames printed in different colors, it is normally easier to name the print c olor when it is congruent with the initial letter of the color name than wh en it is not [10]. The patient could discriminate the initial letters of th e words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tes ts of letter reading. We suggest that the consciously perceived colors acti vated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious proc essing of visual inputs corresponding to the activated letter representatio ns.