Selective deficits of vibrotactile sensitivity in dyslexic readers

Developmental dyslexia is a disability of literacy skill that has also been associated with sensory processing deficits, primarily for the detection o f dynamic auditory and visual stimuli. Here we examined whether analogous d eficits extend into the domain of somatosensory perception. Detection thres holds for each of three frequencies of vibration were obtained for 11 reade rs with a prior history of dyslexia and 14 similarly aged adult controls. T he poor readers were significantly less sensitive to vibration at 3 Hz (P < 0.01) but not at either 30 or 100 Hz. Detection of each of these three vib ration rates is mediated primarily by a separate somatosensory fiber tract; deficits selective to 3 Hz therefore suggest an impairment within the slow -adapting I(SAI) fiber system beginning with Merkel-cell mechanoreceptors i n the glabrous skin. Such evidence is compatible with the hypothesis of a g eneralized, multisensory deficit of temporal processing functions in dyslex ia. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.