Investigating the ‘Atypical Rhythm Risk’ hypothesis in children with developmental language disorder using an EEG rhythmic speech paradigm

Sensitivity to rhythmic and prosodic cues in speech has been described as a precursor of language acquisition. Consequently, atypical rhythmic processing during infancy and early childhood has been considered a risk factor for developmental language disorders. This is the ‘atypical rhythm risk’ (ARR) hypothesis. The neural processing of rhythmic speech has not yet been explored in children with developmental language disorder (DLD). Here we utilise EEG and a rhythmic speech paradigm previously utilised for dyslexia to investigate the ARR hypothesis in 9-year-old children with and without DLD. We investigate angular velocity, power, ERPs, phase-amplitude coupling (PAC) and phase-phase coupling (PPC), at three frequency bands, delta, theta and low gamma. Both groups demonstrated significant and equivalent phase entrainment in the delta and theta bands, but only the control children showed significant phase entrainment in the low gamma band. Further, while angular velocity in the delta and theta bands was equivalent by group, there was a significant gamma-band difference. The children with DLD also exhibited significantly more theta and gamma power compared to the control children. Regarding PAC and PPC, both groups showed significant and equivalent coupling strength. However, group resultant phase differences showed that low-frequency phase (delta and theta) affected gamma oscillations differently by group. The EEG data show important differences between children with and without DLD in the neural mechanisms underpinning the processing of rhythmic speech. The findings are discussed in terms of auditory theories of DLD.