Neglect and visual recognition.

Abstract

B.Q., a right-handed woman who had suffered a stroke affecting the right parietal region, showed visuospatial neglect and problems in recognizing seen objects and faces. Investigation of her visual recognition problems revealed a striking inability to identify the left sides of chimaeric objects and faces. Often, B.Q. would deny that the stimulus was chimaeric at all, and she was remarkably poor (though above chance) at discriminating chimaeric from normal faces. Even when left-sided details had been accurately traced or described, they were often either ignored in reporting the identities of the constituent parts of a chimaeric or assimilated in some way to the information from the right side. Neglect of the left side was more pronounced for chimaerics which approximated an individual face or object. It occurred regardless of the chimaeric's position in B.Q.'s field of vision, and was found with brief (200 ms) presentations of stimuli confined to her (perimetrically intact) right visual field. When chimaeric faces were inverted, B.Q. continued to neglect the side of the chimaeric falling to her left, which implies that the neglect did not operate in entirely object-centered coordinates. However, left-sided information could be used if it was critical in determining the identity of an object or a face. We suggest that this could explain B.Q.'s lack of neglect of individual words, for which left-sided (initial) letters are often crucial to successful recognition. An account of her deficit is proposed, involving an interaction between moderately defective pick-up of left-sided information in an object-based coding system and preserved access to stored representations of familiar visual stimuli.