Assistive listening devices drive neuroplasticity in children with dyslexia

Children with dyslexia often exhibit increased variability in sensory and cognitive aspects of hearing relative to typically developing peers. Assistive listening devices (classroom FM systems) may reduce auditory processing variability by enhancing acoustic clarity and attention. We assessed the impact of classroom FM system use for 1 year on auditory neurophysiology and reading skills in children with dyslexia. FM system use reduced the variability of subcortical responses to sound, and this improvement was linked to concomitant increases in reading and phonological awareness. Moreover, response consistency before FM system use predicted gains in phonological awareness. A matched control group of children with dyslexia attending the same schools who did not use the FM system did not show these effects. Assistive listening devices can improve the neural representation of speech and impact reading-related skills by enhancing acoustic clarity and attention, reducing variability in auditory processing.Children with dyslexia, reading impairment not caused by deficits in ability or opportunity (1), often have difficulties with orienting and maintaining attention (2, 3). Although the ability to direct attention is still developing during the elementary school years (4), dyslexics have poorer task-dependent attentional shifting in both auditory and visual modalities than their typically developing peers even into adulthood (2, 3). These deficits may impact and be impacted by heightened variability in sensory processes, such as inconsistent representations of speech by the auditory nervous system, and could contribute to documented impairments in auditory processing (5–7) and difficulty with meaningfully disambiguating speech sounds (8). Children with dyslexia can exhibit abnormal subcortical processing of speech, particularly in response to acoustic elements crucial for differentiating speech sounds (9–11). Deficient auditory sensory representation and unsuccessful disambiguation of speech likely contribute to the well-documented impairments in phonological awareness and phonological memory seen in children with dyslexia (12–14), with auditory processing skills in prereaders predicting later language skill (15, 16). Because the auditory system integrates both sensory and cognitive facets of hearing, we suggest that through repeated, impaired interaction with sound, children with dyslexia can develop abnormal sensory representations of speech as well as abnormal cognitive skills for the interpretation of speech. For example, a child who repeatedly misperceives the sounds “cat” as “bat” or “pat” fails to make a robust sound-to-meaning connection between those sounds and their referent. However, because of this same integrative nature of the auditory system, deficient function can be improved with auditory training.Auditory perception and neurophysiology can be altered with auditory training (17–23). These changes can be traced directly to cross-cortical and descending cortical influence on neural receptivity in animal models and are driven by the behavioral importance of sounds (18, 24). In humans, attention and working memory are important components of training-related changes (25) and may serve to direct descending cortical influence on auditory sensory function. Computer-based perceptual games, musical training, and language learning can provide effective training for children with developmental learning disorders, such as dyslexia, because they actively engage attention to sound. Classroom assistive listening devices, which can be worn throughout the school day, can also improve auditory processing by engendering enhancements in attention, as reported by both teachers and students (26–28). Assistive listening devices (i.e., classroom FM systems) also result in neurophysiologic enhancements in response to attended vs. ignored sounds (29). Such systems increase the signal-to-noise ratio of the speaker of interest (e.g., the teacher) (30) and create a more stable acoustic input by reducing the impact of background noise on the most vulnerable portion of speech sounds (31). These acoustic enhancements, along with accompanying improvements in auditory attention, lead to boosts in academic achievement, literacy, and phonological awareness, with the greatest benefits seen for children with learning impairments (32–34).What are the biological mechanisms by which classroom FM system use improves auditory attention and phonological awareness in children with dyslexia? How might these benefits translate to the neural representation of speech? Here, we investigated the impact of classroom FM system use on auditory brainstem encoding of stop consonants, which can be deficient in children with dyslexia. Auditory brainstem function is stable from test to retest in the absence of intervention (35, 36), but can be altered by short-term auditory training (19, 20, 22), lifelong experience such as musical training and language experience (37, 38), and directed attention (39). Here we assessed auditory brainstem responses and reading performance in children with dyslexia before and after classroom FM system use for one academic year. We hypothesized that enhanced neural consistency would accompany improvement in reading skills in children wearing the FM systems but not in a control group of dyslexic children in the same classrooms who did not wear assistive listening devices. We further hypothesized that neural consistency would improve pervasively throughout the recording session and not simply offset neural fatigue.