Intact verbal description of letters with diminished awareness of their forms

Visual processing and its conscious awareness can be dissociated. To examin e the extent of dissociation between ability to read characters or words an d to be consciously aware of their forms, reading ability and conscious awa reness for characters were examined using a tachistoscope in an alexic pati ent. A right handed woman with 14 years of education presented with incompl ete right hemianopia, alexia with kanji (ideogram) agraphia, anemia, and am nesia. Brain MRI disclosed cerebral infarction limited to the left lower ba nk of the calcarine fissure, lingual and parahippocampal gyri, and an old i nfarction in the right medial frontal lobe. Tachistoscopic examination disc losed that she could read characters aloud in the right lower hemifield whe n she was not clearly aware of their forms and only noted their presence va guely Although her performance in reading kanji was better in the left than the right held, she could read kana (phonogram) characters and Arabic nume rals equally well in both fields. By contrast, she claimed that she saw onl y a flash of light in 61% of trials and noticed vague forms of stimuli in 3 6% of trials. She never recognised a form of a letter in the right lower he ld precisely. She performed judgment tasks better in the left than right lo wer hemifield where she had to judge whether two kana characters were the s ame or different. Although dissociation between performance of visual recog nition tasks and conscious awareness of the visual experience was found in patients with blindsight or residual vision, reading (verbal identification ) of characters without clear awareness of their forms has not been reporte d in clinical cases. Diminished awareness of forms in our patient may refle ct incomplete input to the extrastriate cortex.