Rhythmic priming: A stimulus-brain coupling analysis in adults with dyslexia and matched controls
Résumé
Music and language contain rhythmic regularities that allow for temporal prediction. The regularity of music rhythm makes it an ideal stimulus to entrain neural oscillations, and research has shown that the brain oscillates to frequencies present in the stimulus. The dynamic attending theory (DAT) predicts that entrained oscillations persist after the external stimulus has stopped, suggesting that entrainment to rhythmic stimuli can influence subsequent perception. Indeed, research has shown that speech perception can be influenced by a previous rhythm, via increased stimulus brain-coupling. Research has also shown that neural rhythmic entrainment to the beat is atypical in individuals with dyslexia. In the present rhythmic priming study, electroencephalography was recorded to investigate whether (1) the brain responds in a non-linear way to the beat level of a rhythmic stimulus; (2) regular compared to irregular rhythmic primes influence subsequent speech perception in a grammaticality judgement task; and (3) these results differ for control and dyslexic adults. Controls (n = 12) and dyslexics (n = 13) showed enhanced stimulus-brain coherence to regular compared to irregular rhythms, and a nonlinear transformation was observed between stimulus and neural representation wherein the beat level was overrepresented in the brain compared to the acoustic signal. There were no differences between groups in stimulus-brain coherence. However, an FFT analysis of the EEG data revealed that while the boosting of the beat level (2Hz) in the neural representation was visible for controls, dyslexics showed a more linear transformation of the sound acoustic features, with a greater response to the 4Hz acoustic information. For the target sentences presented after the rhythmic primes, preliminary data suggest that stimulus-brain coherence was enhanced at the 2Hz, stressed syllable rate after regular compared to irregular primes for dyslexics. These results will be discussed in relation to DAT and observed rhythmic processing deficits in dyslexia.