Print Exposure Interaction with Neural Tuning on Letter/Non-Letter Processing During Literacy Acquisition: An ERP Study on Dyslexic and Typically Developing Children

Background/Objectives: The first step in learning an alphabetic writing system is to establish letter–sound associations. This process is more difficult for children with dyslexia (DYS) than for typically developing (TD) children. Cerebral mechanisms underlying these associations are not fully understood and are expected to change during the training course. This study aimed to identify the neurophysiological correlates and developmental changes of visual letter processing in children with DYS compared to TD children, using event-related potentials (ERPs) during a letter/non-letter classification task. Methods: A total of 71 Russian-speaking children aged 7–11 years participated in the study, including 38 with dyslexia and 33 TD children. The participants were divided into younger (7–8 y.o.) and older (9–11 y.o.) subgroups. EEG recordings were taken while participants classified letters and non-letter characters. We analyzed ERP components (N/P150, N170, P260, P300, N320, and P600) in left-hemisphere regions of interest related to reading: the ventral occipito-temporal cortex (VWFA ROI) and the inferior frontal cortex (frontal ROI). Results: Behavioral differences, specifically lower accuracy in children with dyslexia, were observed only in the younger subgroup. ERP analysis indicated that both groups displayed common stimulus effects, such as a larger N170 for letters in younger children. However, their developmental trajectories diverged. The DYS group showed an age-related increase in the amplitude of early components (N/P150 in VWFA ROI), which contrasts with the typical decrease observed in TD children. In contrast, the late P600 component in the frontal ROI revealed an age-related decrease in the DYS group, along with overall reduced amplitudes compared to their TD peers. Additionally, the N320 component differentiated stimuli exclusively in the DYS group. Conclusions: The data obtained in this study confirmed that the mechanisms of letter recognition in children with dyslexia differ in some ways from those of their TD peers. This atypical developmental pattern involves a failure to efficiently specialize early visual processing, as evidenced by the increasing N/P150. Additionally, there is a progressive reduction in the cognitive resources available for higher-order reanalysis and control, indicated by the decreasing frontal P600. This disruption in neural specialization and automation ultimately hinders the development of fluent reading.