Wider neural tuning is suggested to underlie dyslexics' visual and auditory perception

Abstract

Evidence is accumulating to demonstrate that dyslexics and ordinary readers (OR) differ in visual and in auditory perception on various perceptual tasks. Are there perceptual tasks that could be considered analogous in visual and auditory perception, that also show similar differences between dyslexics and OR? If so, what underlies their processing? In order to answer these questions we measured 22 Italian children (13 dyslexics and 9 OR) in visual and auditory tasks. The form-resolving field (FRF) measured the extent of visual perception by tachistoscopically presenting two letters simultaneously, one always at the center of gaze and the other in the periphery, at different eccentricities. The auditory measure — the cocktail party effect — comprised 4 parts: 1. recognizing the spoken central stimuli alone, 2. recognizing it in the presence of surrounding speech-mask, 3. the same with white noise as mask, and 4. repeating condition 2 while asking the subjects to report the central stimuli and the words perceived from the speech-mask. Dyslexic children had a wider extent of visual perception of letters. Analogously in auditory perception, both groups reported correctly about the same amount of words spoken from the central stimuli, but dyslexics reported significantly less words than OR in the presence of speech-mask. However, the ratio of words perceived from the surrounding speech-mask to that of the ones perceived from the center is much larger for the dyslexics, suggesting wider auditory perception. Individual analysis has shown that over 80% of dyslexics had wide visual and auditory perception. We suggest that the wider visual and auditory perception indicate wider neural tuning and reduced neural selectivity in dyslexics as a consequence of interactions between the incoming sensory signals and the attentional processes. As this occurs in both sensory modalities, in most dyslexic individuals, we suggest the notion of a general perceptual strategy.

Footnotes

 We thank Matteo Cavalleri for excellent technical help.