Abstract:

Developmental dyslexia is a neurological disorder characterized by a specific deficit in reading, despite adequate intelligence and socioeconomic opportunity. A large number of studies have revealed that dyslexics usually exhibit impaired auditory temporal processing. At the behavioral level, dyslexics struggle to discriminate the sequence of rapid and successive stimuli as well as dynamical temporal characteristics. At the neural level, dyslexics evoke weaker mismatch negativity (MMN) and have abnormal neural synchronization. These deficits have been found in the processing of both verbal and non-verbal stimuli, suggesting that such deficits are not specific to speech processing. However, the auditory temporal-order processing deficits of dyslexia are manifested in the processing of both rapidly and slowly presented auditory stimuli. Besides, dyslexic children have more abnormal neural synchronization in low-frequency temporal modulation, and dyslexic adults have more abnormal neural synchronization in high-frequency temporal modulation. Therefore, auditory temporal processing deficits of dyslexia seem to occur not only in a narrow temporal window, but also in a wider temporal window. The developmental characteristics of dyslexia may also imply that the temporal window of auditory temporal processing deficits will narrow with age. Moreover, only the neural mechanism of dyslexics while distinguishing deviant auditory temporal stimuli has been examined in previous studies, and there is still a lack of research, such as the neural mechanism of more general auditory temporal processing and the changing process of such a neural mechanism over time.

In summary, the following questions need to be elucidated in further studies. 1) The temporal windows in which auditory temporal processing deficits occur in dyslexia, and how will they change with age. It is generally known that different temporal windows (e.g., 40 ~ 4000 ms) correspond to different levels of language abstractions (e.g., phonetic feature, segment, syllable, word, metrical foot and prosodic phrase), and the cross-language phonological awareness is developed from larger-grained phonological units (such as stressed syllables) to smaller granular phonetic units (such as phonemes). Based on this, it can be inferred that the auditory temporal processing deficits of developmental dyslexia may only exist in temporal windows corresponding to language abstractions, which may gradually narrow with age. In the future, a cross-sectional and longitudinal study can be implemented to investigate this question. 2) What is the neural time course of auditory temporal processing deficits in dyslexia. N1, P2, CNV (contingent negative variation) and LPCt (late positive component of timing) correspond to selective attention, cognitive resource allocation, temporal encoding and temporal discrimination of the temporal processing, respectively. However, the current electrophysiological studies have only confirmed the existence of auditory temporal processing deficits among dyslexics through mismatch negativity waves, while the processing stage in which the auditory temporal deficits occur has not been ascertained. Aftertime, event-related potential (ERP) technology with a high temporal resolution can be used to explore this question. 3) Whether auditory temporal processing deficits are core causes of dyslexia. Previous studies have shown that dyslexics are also accompanied by deficits in attention and working memory, while the effects brought by differences in their attention and working memory were not excluded from tasks such as temporal order judgment (TOJ) used in previous studies. Control conditions can be set in future studies to explore whether auditory temporal processing deficits are the primary deficits that cause developmental dyslexia.

Key words: developmental dyslexia, auditory temporal processing, temporal sequence, dynamic temporal feature, mismatch, neural synchronization