Abstract
Research on children and adults with developmental dyslexia—a specific difficulty in learning to read and spell—suggests that phonological deficits in dyslexia are linked to basic auditory deficits in temporal sampling. However, it remains undetermined whether such deficits are already present in infancy, especially during the sensitive period when the auditory system specializes in native phoneme perception. Because dyslexia is strongly hereditary, it is possible to examine infants for early predictors of the condition before detectable symptoms emerge. This study examines low-level auditory temporal sampling in infants at risk for dyslexia across the sensitive period of native phoneme learning. Using magnetoencephalography (MEG), we found deficient auditory sampling at theta in at-risk infants at both 6 and 12 months, indicating atypical auditory sampling at the syllabic rate in those infants across the sensitive period for native-language phoneme learning. This interpretation is supported by our additional finding that auditory sampling at theta predicted later vocabulary comprehension, nonlinguistic communication and the ability to combine words. Our results indicate a possible early marker of risk for dyslexia.
Highlights
Cortical oscillations are believed to play an important role in several aspects of human cognition, including attention, learning, object recognition, sensory feature binding, and emotional evaluation, and in context of the present work, speech perception and processing [1,2,3,4]
Some insight is offered by research on infants at risk for specific language impairment (SLI; suggested to share some genetic etiology with dyslexia) who showed atypical right-hemispheric theta and gamma processing in response to rapidly presented sounds at 6 months and its link to later expressive vocabulary [39]. These results suggest that infants at risk for dyslexia may already have an altered oscillatory response before they enter the critical period of native language learning, and it remains to be seen whether this response will change over the course of the sensitive period of native language learning
Investigating oscillatory functioning underlying auditory sampling in dyslexia is an important aspect for early detection and for designing tailored interventions for children at risk for dyslexia before they enter school
Summary
Cortical oscillations are believed to play an important role in several aspects of human cognition, including attention, learning, object recognition, sensory feature binding, and emotional evaluation, and in context of the present work, speech perception and processing [1,2,3,4]. In children and adults with dyslexia, neural encoding of the speech signal was found to be impaired at delta/theta (1–8 Hz) and gamma (>30 Hz), both modulation frequency rates necessary for accurate speech perception [13,14,15,16,17,18,19,20,21,22,23,24,25,26]. The development of accurate auditory sampling in the infant brain has been implicated to contribute to later precise processing of spectrotemporal features of speech sounds, the generation of native phoneme representations, and later language and reading skills [11,27]. They found that theta and gamma rhythms can be used as markers for the development of native-language phoneme perception across the so-called sensitive period, a period that is characterized by infants’ initial ability, at 6 months, to perceive phonetic contrasts used to differentiate words across all languages, and at 12 months, to show a narrowing of their speech perception abilities as they begin to focus on phonetic units in the language(s) to which they are exposed [33,34,35,36,37,38]
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