Successful vocabulary acquisition requires encoding of newly learned spoken words into a long-term storage. At the neural level, this means optimal establishment of novel neural connections and rapid formation of memory traces for words. In adults the rapid formation of memory traces is seen as an enhanced neural response at 50 ms after word recognition point to novel words after short exposure.
To explore the rapid word memory trace formation in children with dyslexia, we recorded online neural activity using electroencephalography (EEG) and event-related potentials (ERPs) during a short (~35mins) session of passive exposure to a novel pseudo-word in school-aged dyslexic children and matched fluently reading controls. The memory trace formation for the novel word was investigated by comparing the average ERPs of trials in the early and late part of the exposure.
In fluently reading children, the neural response to the unfamiliar pseudo-word at early latencies after word disambiguation point increased significantly by the end of the session, putatively indicating memory trace formation for the novel word. In contrast, the neural response at the early latencies did not show any change in the group with dyslexia between the early and late stages of the exposure, indicating impaired rapid formation of memory traces for novel words. We propose that rapid neural learning of new spoken words is impaired in dyslexic children, possibly due to deficient phonological processing, development of phonological representations and phonological short-term memory, and hinders efficient vocabulary growth
