Phonological memory and word learning deficits in children with specific language impairment: A role for perceptual context?

A role for incidental auditory learning in auditory-visual word learning among kindergarten children

This study focused on the potential role of incidental, auditory perceptual learning in among children learning new words. To this end, we examined how irrelevant auditory similarities across words, that provide no cues regarding their visual or conceptual attributes, influence pseudo-word learning in a name/picture matching paradigm. Two types of irrelevant auditory similarities were used: shared sequences of vowels or consonants. Learning word-to-picture associations in these two conditions was compared to a baseline condition in which items did not share either sequence. Kindergarten children readily learned items in all conditions, but auditory similarity interfered with learning (odds ratio, 1.12). Individual differences in reasoning and vocabulary did not account for the interference effect. These findings suggest that the sensory properties of words continue to influence language learning during the preschool years through rapid incidental learning, even if the effect is relatively small. Consistent with previous studies in the visual modality, we now suggest that incidental perceptual learning occurs in the auditory modality. Furthermore, the current findings suggest that this learning can interfere with word learning, highlighting the importance of the perceptual structure of words in real-world-like learning environments.

Impaired neural mechanism for online novel word acquisition in dyslexic children

Developmental dyslexia is characterised as an inability to read fluently. Apart from literacy problems, dyslexics have other language difficulties including inefficient speech encoding and deficient novel word learning. Yet, the neural mechanisms underlying these impairments are largely unknown. We tracked online formation of neural memory traces for a novel spoken word-form in dyslexic and normal-reading children by recording the brain’s electrophysiological response dynamics in a passive perceptual exposure session. Crucially, no meaning was assigned to the new word-form nor was there any task related to the stimulus, enabling us to explore the memory-trace formation of a purely phonological form in the absence of any short-term or working memory demands. Similar to previously established neural index of rapid word learning in adults, the control children demonstrated an early brain response enhancement within minutes of exposure to the novel word-form that originated in frontal cortices. Dyslexic children, however, lacked this neural enhancement over the entire course of exposure. Furthermore, the magnitude of the rapid neural enhancement for the novel word-form was positively associated with reading and writing fluency. This suggests that the rapid neural learning mechanism for online acquisition of novel speech material is associated with reading skills. Furthermore, the deficient online learning of novel words in dyslexia, consistent with poor rapid adaptation to familiar stimuli, may underlie the difficulty of learning to read.

The dynamic imprint of word learning on the dorsal language pathway

According to Hickok and Poeppel (2007), the acquisition of new vocabulary rests on the dorsal language pathway connecting auditory and motor areas. The present study tested this hypothesis longitudinally by measuring BOLD signal changes during a verbal repetition task and modulation of resting state functional connectivity (rs-FC) in the dorsal stream. Thirty-five healthy participants, divided into trained and control groups, completed fMRI sessions on days 1, 10, and 24. Between days 1 and 10, the trained group learned 84 new pseudowords associated with 84 native words. Task-related fMRI results showed a reduced activity in the IFG and STG while processing the learned vocabulary after training, returning to initial values two weeks later. Moreover, rs-fMRI analysis showed stronger rs-FC between the IFG and STG in the trained group than in the control group after learning, especially on day 24. These neural changes were more evident in participants with a larger vocabulary. Discussion focuses on the prominent role of the dorsal stream in vocabulary acquisition. Even when their meaning was known, newly learned words were again processed through the dorsal stream two weeks after learning, with the increase in rs-FC between auditory and motor areas being a relevant long-term imprint of vocabulary learning.