Abstract:

The “Dyslexia Paradox”, caused by the relatively later diagnosis of developmental dyslexia (DD) than the optimal intervention period, has always been a challenge in research on children's reading development disorders. The core deficit of DD is phonological awareness, which is essentially caused by more fundamental auditory processing deficits. Rhythm, as one of the main influencing factors of auditory processing, occurs early in an individual's life and is also a key indicator of children's language acquisition. It not only affects children's oral development but also plays an important role in children's decoding, reading comprehension, and writing. Previous studies have found that children with DD exhibit behavioral and neural characteristics of atypical rhythm. Specific behavioral characteristics include worse sensitivity and accuracy in rhythm perception; high rates of rhythm synchronization and reproduction errors, missed beats, and significantly shorter durations; longer prediction intervals and weaker neo-alternative intervals to stimulate neural responses; and an inability to differentiate between rhythmically related slower rise time, resulting in impaired information about speech flow etc. Specific neural activity characteristics include atypical δ-band neural entrainment; low synchronization of amplitude modulation in the low-frequency bands of the brain; and abnormal auditory-motor coupling. Based on this, the causal relationship between atypical rhythm and written disorder in DD children is further revealed: 1) atypical rhythm impede early word decoding. Unlike TD children, most reading and spelling (dictation) failures in DD children are due to decoding failures caused by rhythm perception defects. When rhythm production is atypical, decoding ability is also affected. 2) Atypical rhythm affects DD children's reading comprehension. The prediction deficit in DD children is inferior to that of TD peers, and the number of syllables read per second is also lower, reducing reading efficiency. The prediction deficit also makes it difficult for them to effectively use morphosyntactic information to predict upcoming words and complex language structures, making it difficult to ensure reading fluency and accuracy. 3) Atypical rhythm affects the writing efficiency of DD children. Writing is a rhythmic activity. Compared with TD peers, DD children take significantly longer to write individual letters of a word, and they are unable to adjust the writing time of individual letters and the overall writing speed as required, which makes it difficult for them to accurately and fluently complete a series of rhythmic events related to the content of the writing in a limited period of time. In summary, rhythm perception deficits in DD children can predict defects in their reading processing mechanisms. This fully demonstrates that atypical rhythm may be an earlier and deeper risk factor for DD, and can be considered as a potential identification marker for DD children before formal schooling. Future research can take atypical rhythm as an entry point to explore the individual differences of atypical rhythm in DD children, and actively explore the characteristics and mechanisms of atypical rhythm in Chinese children with DD, so as to provide empirical and theoretical evidence for developing more ecologically valid rhythmic measurement tools and improving the efficiency of the identification of and intervention in DD.

Key words: developmental dyslexia, early identification markers, atypical rhythm