Learning to read shapes the activation of neural lexical representations in the speech recognition pathway

Ongoing Sign Processing Facilitates Written Word Recognition in Deaf Native Signing Children

Signed and written languages are intimately related in proficient signing readers. Here, we tested whether deaf native signing beginning readers are able to make rapid use of ongoing sign language to facilitate recognition of written words. Deaf native signing children (mean 10 years, 7 months) received prime target pairs with sign word onsets as primes and written words as targets. In a control group of hearing children (matched in their reading abilities to the deaf children, mean 8 years, 8 months), spoken word onsets were instead used as primes. Targets (written German words) either were completions of the German signs or of the spoken word onsets. Task of the participants was to decide whether the target word was a possible German word. Sign onsets facilitated processing of written targets in deaf children similarly to spoken word onsets facilitating processing of written targets in hearing children. In both groups, priming elicited similar effects in the simultaneously recorded event related potentials (ERPs), starting as early as 200 ms after the onset of the written target. These results suggest that beginning readers can use ongoing lexical processing in their native language - be it signed or spoken - to facilitate written word recognition. We conclude that intimate interactions between sign and written language might in turn facilitate reading acquisition in deaf beginning readers.

How are visemes and graphemes integrated with speech sounds during spoken word recognition? ERP evidence for supra-additive responses during audiovisual compared to auditory speech processing

Both visual articulatory gestures and orthography provide information on the phonological content of speech. This EEG study investigated the integration between speech and these two visual inputs. A comparison of skilled readers' brain responses elicited by a spoken word presented alone versus synchronously with a static image of a viseme or a grapheme of the spoken word's onset showed that while neither visual input induced audiovisual integration on N1 acoustic component, both led to a supra-additive integration on P2, with a stronger integration between speech and graphemes on left-anterior electrodes. This pattern persisted in P350 time-window and generalized to all electrodes. The finding suggests a strong impact of spelling knowledge on phonetic processing and lexical access. It also indirectly indicates that the dynamic and predictive value present in natural lip movements but not in static visemes is particularly critical to the contribution of visual articulatory gestures to speech processing.

Phonemic Training Modulates Early Speech Processing in Pre-reading Children

Phonemic awareness and rudimentary grapheme knowledge concurrently develop in pre-school age. In a training study, we tried to disentangle the role of both precursor functions of reading for spoken word recognition. Two groups of children exercised with phonemic materials, but only one of both groups learnt corresponding letters to trained phonemes. A control group exercised finger-number associations (non-linguistic training). After the training, we tested how sensitive children were to prime-target variation in word onset priming. A group of young adults took part in the same experiment to provide data from experienced readers. While decision latencies to the targets suggested fine-grained spoken word processing in all groups, event-related potentials (ERPs) indicated that both phonemic training groups processed phonemic variation in more detail than the non-linguistic training group and young adults at early stages of speech processing. Our results indicate temporal plasticity of implicit speech processing in pre-school age as a function of explicit phonemic training.

Children at risk for dyslexia show deficient left-hemispheric memory representations for new spoken word forms

Developmental dyslexia is a specific learning disorder with impairments in reading and spelling acquisition. Apart from literacy problems, dyslexics show inefficient speech encoding and deficient novel word learning, with underlying problems in phonological processing and learning. These problems have been suggested to be related to deficient specialization of the left hemisphere for language processing. To examine this possibility, we tracked with magnetoencephalography (MEG) the activation of the bilateral temporal cortices during formation of neural memory traces for new spoken word forms in 7-8-year-old children with high familial dyslexia risk and in controls. The at-risk children improved equally to their peers in overt repetition of recurring new word forms, but were poorer in explicit recognition of the recurring word forms. Both groups showed reduced activation for the recurring word forms 400-1200 ms after word onset in the right auditory cortex, replicating the results of our previous study on typically developing children (Nora et al., 2017, Children show right-lateralized effects of spoken word-form learning. PLoS ONE 12(2): e0171034). However, only the control group consistently showed a similar reduction of activation for recurring word forms in the left temporal areas. The results highlight the importance of left-hemispheric phonological processing for efficient phonological representations and its disruption in dyslexia.

Phonemic feature involvement in lexical access in grades 3 and 5: Evidence from visual and auditory lexical decision tasks

Numerous studies have evidenced the involvement of the phonological code during visual word recognition not only in skilled adult readers but also in child readers. Moreover, in skilled adult readers, visual word processing has been shown to be sensitive to phonetic details such as phonemic features (e.g., manner of articulation, place of articulation, voicing and nasality in French) which are typically involved in phonological lexicon access during speech processing. In contrast, it is not known whether and when visual word recognition is affected by phonemic features during learning to read. The present study investigates this issue in third and fifth graders. A lexical decision task was performed in visual and auditory modalities. Targets were French words (e.g., piano [piano]) and pseudowords created from target words. Mismatching was on the first phoneme. There were one-feature phoneme mismatch pseudowords (e.g., tiano) and multiple-feature phoneme mismatch pseudowords (e.g., liano). The pseudowords were used as a marker of the sensitivity to phonemic features in phonological lexicon access. Phonemic feature effects were found in visual and auditory lexical decision tasks in both grades, indicating that phonological lexicon access involves phonemic features in print processing as in speech processing. In contrast, the absence of difference between both grades seems to indicate that this effect is independent of age or, more precisely, of phonological development and reading performance.

Tracking independence and merging of prosodic and phonemic processing across infancy

Recent evidence suggests division of labor in phonological analysis underlying speech recognition. Adults and children appear to decompose the speech stream into phoneme-relevant information and into syllable stress. Here we investigate whether both speech processing streams develop from a common path in infancy, or whether there are two separate streams from early on. We presented stressed and unstressed syllables (spoken primes) followed by initially stressed early learned disyllabic German words (spoken targets). Stress overlap and phoneme overlap between the primes and the initial syllable of the targets varied orthogonally. We tested infants 3, 6 and 9 months after birth. Event-related potentials (ERPs) revealed stress priming without phoneme priming in the 3-month-olds; phoneme priming without stress priming in the 6-month-olds; and phoneme priming, stress priming as well as an interaction of both in 9-month-olds. In general the present findings reveal that infants start with separate processing streams related to syllable stress and to phoneme-relevant information; and that they need to learn to merge both aspects of speech processing. In particular the present results suggest (i) that phoneme-free prosodic processing dominates in early infancy; (ii) that prosody-free phoneme processing dominates in middle infancy; and (iii) that both types of processing are operating in parallel and can be merged in late infancy.

ERP correlates of word onset priming in infants and young children

Using word onset priming with early learned words, we tracked access to phonological representations and predictive phonological processing at 6, 12, 18, and 24 months after birth. Event-Related Potentials (ERPs) were recorded while participants heard German word onsets (primes) followed by disyllabic spoken words (targets). Primes and target onsets were either congruent or incongruent (ma - Mama vs. so - Mama [Engl. 'mommy']). For an adult control group, ERP differences were found for the N100 complex, which has been related to abstract auditory analysis; and for the P350 deflection, which has been related to lexical access. A combined analysis of all infants and young children revealed an immature instance of an N100 effect, suggesting adult-like abstract speech sound processing. A central negativity effect, which had formerly been obtained when adults or older children were engaged in a lexical decision task, suggests that adult-like predictive phonological processing is available early in infancy. However, the absence of a P350-like effect in the infant data suggests that adult-like access to phonological forms is not established in the first two years of life. Taken together, ERPs recorded in word onset priming proved useful in investigating early phonological processing without an explicit behavioral measure.

Processing of syllable stress is functionally different from phoneme processing and does not profit from literacy acquisition

Speech is characterized by phonemes and prosody. Neurocognitive evidence supports the separate processing of each type of information. Therefore, one might suggest individual development of both pathways. In this study, we examine literacy acquisition in middle childhood. Children become aware of the phonemes in speech at that time and refine phoneme processing when they acquire an alphabetic writing system. We test whether an enhanced sensitivity to phonemes in middle childhood extends to other aspects of the speech signal, such as prosody. To investigate prosodic processing, we used stress priming. Spoken stressed and unstressed syllables (primes) preceded spoken German words with stress on the first syllable (targets). We orthogonally varied stress overlap and phoneme overlap between the primes and onsets of the targets. Lexical decisions and Event-Related Potentials (ERPs) for the targets were obtained for pre-reading preschoolers, reading pupils and adults. The behavioral and ERP results were largely comparable across all groups. The fastest responses were observed when the first syllable of the target word shared stress and phonemes with the preceding prime. ERP stress priming and ERP phoneme priming started 200 ms after the target word onset. Bilateral ERP stress priming was characterized by enhanced ERP amplitudes for stress overlap. Left-lateralized ERP phoneme priming replicates previously observed reduced ERP amplitudes for phoneme overlap. Groups differed in the strength of the behavioral phoneme priming and in the late ERP phoneme priming effect. The present results show that enhanced phonological processing in middle childhood is restricted to phonemes and does not extend to prosody. These results are indicative of two parallel processing systems for phonemes and prosody that might follow different developmental trajectories in middle childhood as a function of alphabetic literacy.

Reading acquisition reorganizes the phonological awareness network only in alphabetic writing systems

It is unknown how experience with different types of orthographies influences the neural basis of oral language processing. In order to determine the effects of alphabetic and nonalphabetic writing systems, the current study examined the influence of learning to read on oral language in English and Chinese speakers. Children (8-12 years olds) and adults made rhyming judgments to pairs of spoken words during functional magnetic resonance imaging (fMRI). Developmental increases were seen only for English speakers in the left hemisphere phonological network (superior temporal gyrus (STG), inferior parietal lobule, and inferior frontal gyrus). The increase in the STG was more pronounced for words with conflicting orthography (e.g. pint-mint; jazz-has) even though access to orthography was irrelevant to the task. Moreover, higher reading skill was correlated with greater activation in the STG only for English speaking children. The effects suggest that learning to read reorganizes the phonological awareness network only for alphabetic and not logographic writing systems because of differences in the principles for mapping between orthographic and phonological representations. The reorganization of the auditory cortex may result in better phonological awareness skills in alphabetic readers.