A variety of reading disability associated with right hemisphere lesions.

Dyslexia, the apparently selective impairment in the ability to read words, or even individual letters, has been repeatedly described in association with left (major) hemisphere lesions. Verbal dyslexia, affecting the reading of words but not of isolated letters, may be characterized by paralexic errors (misreading of words). The paralexias may accompany similar (paraphasic) errors in spoken speech, and be secondary to a more general disorder of language function. They may occur in the 'parietal dyslexia' of Herrmann and Potzl (1926) described as involving 'the frequent intrusion of incorrect words or word fragments in place of the ones actually in the text'. Patients with 'spelling dyslexia' in the absence of aphasia (Wolpert, 1924), who can only read words letter by letter because of a pathological limitation of their ability to perceive forms simultaneously, which prejudices the simultaneous perception of the whole word (Kinsbourne and Warrington, 1962a), make paralexic errors if they try to maintain normal reading speed. In contrast, patients with right-sided (minor hemisphere) damage, though sometimes liable to lose their place on the printed line (Paterson and Zangwill, 1944), have not been reported to show verbal dyslexia. Below are described six right-handed patients with acquired right hemisphere lesions who suffered from reading disability. The paralexic errors were of a very characteristic, consistent, and hitherto undescribed type. They could be reproduced experimentally in a predictable fashion under the controlled conditions of tachistoscopic presentation of written material.