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Poster C7, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall

Heterogeneous neural deficits in dyslexia during speech sound processing tasks

Tracy Centanni1,2, Sara Beach2,3, Ola Ozernov-Palchik2, Sidney May2,4, John Gabrieli2;1Texas Christian University, 2Massachusetts Institute of Technology, 3Harvard University, 4Boston College

In dyslexia, the double deficit hypothesis suggests that children who struggle to acquire reading exhibit deficits in phoneme processing, rapid automatized naming, or both. Auditory processing a critical skill for letter-sound matching, with speed on these tasks directly related to fluency. Recent work suggests that these two deficits may be caused by different dyslexia susceptibility genes and may manifest in unique patterns of brain activation. In the current study, we designed three tasks to differentiate between individuals with dyslexia who have increased neural variability to sound versus those who have difficulty processing rapid auditory stimuli. Two tasks consisted of a ten-step consonant continuum between the sounds /b/ and /d/. In the passive condition, participants listened to the randomized presentation of these sounds while pressing a button in response to nature scenes. In the attention condition, participants pressed one of two buttons to categorize each stimulus as /b/ or /d/. The third task presented three sets of auditory stimuli at 4 different speeds, with participants making sense/nonsense judgements; sentences with semantic content, strings of consonant-vowel-consonant sounds with no semantic content, and amplitude modulated white noise. Adults with (N = 25) and without dyslexia (N = 22) were assessed and then tested on these tasks while magnetoencephalography (MEG) data were acquired. Data were analyzed for consistency across individual trials and the average signal in the low gamma range to correspond with phoneme-level processing. When listening to speech sounds passively, adults with dyslexia exhibited significantly poorer trial-by-trial consistency in the superior temporal gyrus (STG) compared to typically-reading controls (unpaired, two-tail t-test, p = 0.0017). As has been reported previously during passive listening tasks, approximately half of the dyslexia sample drove this group difference. During the identification task, which required attention and access to phonological representations, there was no group difference in neural response consistency (p = 0.23). In the rapid speech task, we observed a behavioral effect where approximately 50% of adults with dyslexia fell to chance performance at rapid speeds when the sentences contained no semantic context, while only 20% of controls exhibited this decline in performance. There were no group differences when semantic information was available or during the noise condition. We also observed group differences on low gamma asymmetry in the STG, especially during the stimuli without semantic context. These findings further support the double-deficit hypothesis and demonstrate that within a population of individuals with dyslexia, the brain and behavioral deficits observed vary widely. Future research should investigate the link between these biological mechanisms and reading outcomes.

Themes: Disorders: Developmental, Perception: Auditory
Method: Electrophysiology (MEG/EEG/ECOG)

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