Levels of representation, co-ordinate frames, and unilateral neglect

Abstract

Abstract We describe the performance of a brain-damaged subject, NG, who made reading errors only on the right half of words. This problem persisted even when the subject had demonstrated accurate recognition of die letters in a stimulus through naming all the letters. Furthermore, the spatially determined reading impairment was unaffected by topographic transformations of stimuli: identical performance was obtained for stimuli presented in horizontal, vertical, and mirror-reversed form. The same pattern of errors was also obtained in all forms of spelling tasks: written spelling, oral spelling, and backward oral spelling. The performance of the subject is interpreted in the context of a multi-stage model of the word recognition process. It is concluded that the locus of the deficit responsible for NG's reading impairment is at a stage of processing where word-centred grapheme representations are computed. The spatially determined pattern of performance reported for NG, as well as other patterns observed for other brain-damaged subjects, are interpreted as providing support for the proposed multi-stage model of word recognition. The more general implications of the reported results for models of visual processing and attention are also considered.