Abstract
Dyslexia is associated with abnormal performance on many auditory psychophysics tasks, particularly those involving the categorization of speech sounds. However, it is debated whether those apparent auditory deficits arise from (a) reduced sensitivity to particular acoustic cues, (b) the difficulty of experimental tasks, or (c) unmodeled lapses of attention. Here we investigate the relationship between phoneme categorization and reading ability, with special attention to the nature of the cue encoding the phoneme contrast (static versus dynamic), differences in task paradigm difficulty, and methodological details of psychometric model fitting. We find a robust relationship between reading ability and categorization performance, show that task difficulty cannot fully explain that relationship, and provide evidence that the deficit is not restricted to dynamic cue contrasts, contrary to prior reports. Finally, we demonstrate that improved modeling of behavioral responses suggests that performance does differ between children with dyslexia and typical readers, but that the difference may be smaller than previously reported.
Highlights
Dyslexia is a learning disability that affects between 5% and 17% of the population and poses a substantial economic and psychological burden for those affected[1,2,3]
Subjects were divided into three groups (Dyslexic, Below Average, and Above Average readers) to be consistent with previous studies that have reported group comparisons, and reading score (as indexed by the Woodcock Johnson Basic Reading Skills standard score (WJ-BRS)) was treated as a continuous variable in line with the perspective that dyslexia represent the lower end of a continuous distribution[69]
Many previous studies have claimed to show a relationship between dyslexia and poor categorical perception of speech phonemes, while others have suggested that the apparent auditory or linguistic processing impairments are the result of general attention or memory deficits that manifest because of task difficulty
Summary
Dyslexia is a learning disability that affects between 5% and 17% of the population and poses a substantial economic and psychological burden for those affected[1,2,3]. A low-level auditory processing deficit disrupts the formation of a child’s internal model of speech sounds (phonemes) during early language learning; later, when young learners attempt to associate written letters (graphemes) with phonemes, they struggle because their internal representation of phonemes is compromised[10] In line with this hypothesis, many studies report group differences between dyslexics and typical reading control participants in auditory psychophysical tasks including amplitude modulation detection[11,12,13,14,15], frequency modulation detection[16,17,18,19,20], rise time discrimination, and duration discrimination[21,22,23,24,25]. Correspondence and requests for materials should be addressed to G.E.O. (email: eobrien3@ uw.edu) www.nature.com/scientificreports/
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