Tactile perception in developmental dyslexia: a psychophysical study usinggratings

Multiple sensory abnormalities have been reported in individuals with devel opmental dyslexia, especially in the visual and auditory systems. We used g ratings of alternating ridges and grooves to investigate tactile perception in this disorder using two tasks: spatial acuity-dependent discrimination of grating orientation and discrimination of gratings varying in ridge widt h. Compared to age-matched normal subjects, dyslexics were significantly im paired on grating orientation discrimination, with mean thresholds that wer e nearly twice normal. Unlike normal subjects, their performance on this ta sk was slightly but significantly worse on the dominant hand than on the no n-dominant hand. Dyslexics also showed a substantial but nonsignificant tre nd for impairment on grating ridge width discrimination. A group of subject s with attention deficit disorder did not differ significantly from normal on any of these measures. These findings expand the range of perceptual def icits reported in developmental dyslexia. Possible explanations for the res ults, including difficulties with temporal processing, abnormal lateral mas king or parietal lobe dysfunction are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.