Atypical Lateralization to Amplitude Modulation in Chinese Adults With Reading Difficulty History

Auditory processing underlies phonological representation and presents neural oscillation lateralization in the brain. Atypical lateralization in auditory processing has been widely accepted as associated with impaired reading skills in alphabetic languages. However, whether Chinese adults with a reading difficulty (RD) history present atypical lateralization in auditory processing similar to that in alphabetic languages remains unknown. The purpose of this study was to investigate whether Chinese adults with poor reading would show atypical lateralization of neural oscillations during auditory sampling.

Thirty-two adults with self-reported RD history and 44 adults without RD history were screened using the Chinese Adult Reading History Questionnaire. Reading accuracy, phonological accuracy, and rapid automatized naming (RAN) were assessed in all the participants. Auditory steady-state responses modulated at 10 to 80 Hz were recorded during a 5.4-sec white noise. Time-frequency power and phase synchrony indices were used to measure induced oscillatory power and synchrony of beta and gamma oscillations related to phonemic processing.

Adults with a RD history performed worse than adults without RD history in reading accuracy and phonological accuracy. Adults with a RD history showed atypical rightward lateralization in the gamma band oscillation, whereas the adults without a RD history showed leftward lateralization. Adults with a RD history also demostrated reduced left-hemisphere oscillatory power and weaker bilateral synchrony. Event-related spectral perturbation in the left hemisphere correlated with reading accuracy in adults with RD history, while left-hemisphere lateralization of event-related spectral perturbation correlated with phonological accuracy in adults without RD history. In adults with RD history, the inter-trial phase synchrony in the left hemisphere correlated with RAN, and inter-trial phase synchrony in the right hemisphere correlated with reading accuracy and RAN, respectively.

Adults with RD history demonstrated atypical rightward gamma band lateralization compared with adults without RD history, alongside reduced left-hemisphere oscillatory power and weaker bilateral synchrony. These neural patterns correlated with reading accuracy and phonological skills, supporting the hypothesis that auditory lateralization deficits underlie phonological processing challenges in Chinese, mirroring mechanisms observed in alphabetic languages.