Multisensory spatial attention deficits are predictive of phonological decoding skills in developmental dyslexia.

Although the dominant approach posits that developmental dyslexia arises from deficits in systems that are exclusively linguistic in nature (i.e., phonological deficit theory), dyslexics show a variety of lower level deficits in sensory and attentional processing. Although their link to the reading disorder remains contentious, recent empirical and computational studies suggest that spatial attention plays an important role in phonological decoding. The present behavioral study investigated exogenous spatial attention in dyslexic children and matched controls by measuring RTs to visual and auditory stimuli in cued-detection tasks. Dyslexics with poor nonword decoding accuracy showed a slower time course of visual and auditory (multisensory) spatial attention compared with both chronological age and reading level controls as well as compared with dyslexics with slow but accurate nonword decoding. Individual differences in the time course of multisensory spatial attention accounted for 31% of unique variance in the nonword reading performance of the entire dyslexic sample after controlling for age, IQ, and phonological skills. The present study suggests that multisensory "sluggish attention shifting"-related to a temporoparietal dysfunction-selectively impairs the sublexical mechanisms that are critical for reading development. These findings may offer a new approach for early identification and remediation of developmental dyslexia.

Visual and auditory attentional capture are both sluggish in children with developmental dyslexia.

Automatic multimodal spatial attention was studied in 12 dyslexic children (SRD), 18 chronological age matched (CA) and 9 reading level matched (RL) normally reading children by measuring reaction times (RTs) to lateralized visual and auditory stimuli in cued detection tasks. The results show a slower time course of focused multimodal attention (FMA) in SRD children than in both CA and RL controls. Specifically, no cueing effect (i.e., RTs difference between cued-uncued) was found in SRD children at 100 ms cue-target delay, while it was present at 250 ms cue-target delay. In contrast, in both CA and RL controls, a cueing effect was found at the shorter cue-target delay but it disappeared at the longer cue-target delay, as predicted by theories of automatic capture of attention. Our results suggest that FMA may be crucial for learning to read, and we propose a possible causal explanation of how a FMA deficit leads to specific reading disability, suggesting that sluggish FMA in dyslexic children could be caused by a specific parietal dysfunction.

Auditory and visual automatic attention deficits in developmental dyslexia.

Several studies have provided evidence for a phonological deficit in developmental dyslexia. However, recent studies provide evidence for a multimodal temporal processing deficit in dyslexia. In fact, dyslexics show both auditory and visual abnormalities, which could result from a more general problem in the perceptual selection of stimuli. Here we report the results of a behavioral study showing that children with dyslexia have both auditory and visual deficits in the automatic orienting of spatial attention. These findings suggest that a deficit of selective spatial attention may distort the development of phonological and orthographic representations that is essential for learning to read.

Wide and diffuse perceptual modes characterize dyslexics in vision and audition.

We examined the performance of dyslexic and typically reading children on two analogous recognition tasks: one visual and the other auditory. Both tasks required recognition of centrally and peripherally presented stimuli. Dyslexics recognized letters visually farther in the periphery and more diffuse near the center than typical readers did. Both groups performed comparably in recognizing centrally spoken stimuli presented without peripheral interference, but in the presence of a surrounding speech mask (the 'cocktail-party effect') dyslexics recognized the central stimuli significantly less well than typical readers. However, dyslexics had a higher ratio of the number of words recognized from the surrounding speech mask, relative to the ones from the center, than typical readers did. We suggest that the evidence of wide visual and auditory perceptual modes in dyslexics indicates wider multi-dimensional neural tuning of sensory processing interacting with wider spatial attention.

The time course of attentional focusing in dyslexic and normally reading children.

A cue size procedure was used to evaluate the time course of visuo-spatial attention in dyslexic and normally reading children. When a stimulus target is presented inside a large cue vs a small cue the identification time is slower. In the present study two cue-target delays (100 and 500 ms) were used. Results showed a slower time course of attentional focusing in dyslexics vs normal readers. Indeed, dyslexics exhibited no cue size effect at a shorter cue-target delay (100 ms), while it was present at a longer cue-target delay (500 ms). In contrast, a cue size effect was found at both cue-target delays in normally reading children. These results further support the hypothesis of sluggish automatic focusing of visual attention in dyslexics. This impairment could be a consequence of a general magnocellular deficit demonstrated previously in dyslexics.