Grapheme-phoneme correspondence in dyslexic and matched control readers

Children with developmental dyslexia have equivalent audiovisual speech perception performance but their perceptual weights differ

As reading is inherently a multisensory, audiovisual (AV) process where visual symbols (i.e., letters) are connected to speech sounds, the question has been raised whether individuals with reading difficulties, like children with developmental dyslexia (DD), have broader impairments in multisensory processing. This question has been posed before, yet it remains unanswered due to (a) the complexity and contentious etiology of DD along with (b) lack of consensus on developmentally appropriate AV processing tasks. We created an ecologically valid task for measuring multisensory AV processing by leveraging the natural phenomenon that speech perception improves when listeners are provided visual information from mouth movements (particularly when the auditory signal is degraded). We designed this AV processing task with low cognitive and linguistic demands such that children with and without DD would have equal unimodal (auditory and visual) performance. We then collected data in a group of 135 children (age 6.5-15) with an AV speech perception task to answer the following questions: (1) How do AV speech perception benefits manifest in children, with and without DD? (2) Do children all use the same perceptual weights to create AV speech perception benefits, and (3) what is the role of phonological processing in AV speech perception? We show that children with and without DD have equal AV speech perception benefits on this task, but that children with DD rely less on auditory processing in more difficult listening situations to create these benefits and weigh both incoming information streams differently. Lastly, any reported differences in speech perception in children with DD might be better explained by differences in phonological processing than differences in reading skills. RESEARCH HIGHLIGHTS: Children with versus without developmental dyslexia have equal audiovisual speech perception benefits, regardless of their phonological awareness or reading skills. Children with developmental dyslexia rely less on auditory performance to create audiovisual speech perception benefits. Individual differences in speech perception in children might be better explained by differences in phonological processing than differences in reading skills.

The influence of temporal asynchrony on character-speech integration in Chinese children with and without dyslexia: An ERP study

Dyslexic readers have been reported to show abnormal temporal acuity and multisensory integration deficiency. Here, we investigated the influence of temporal intervals on Chinese character-speech integration in children with and without dyslexia. Visual characters were presented synchronously to the onset of speech sounds (AV0) or before speech sound by 300 ms (AV300). Event-related potentials (ERP) evoked by congruent condition (speech sounds presented with congruent Chinese characters) and by baseline condition (speech sounds presented with Korean characters) were compared. Typically developing (TD) children exhibited congruency effect in AV0 condition, whereas dyslexic children exhibited congruency effect in AV300 condition. Moreover, congruency effect in TD children was due to enhanced neural activation to congruent trials, congruency effect in dyslexic children was contributed by neural suppression for baseline trials. These results suggested that different underlying mechanisms were involved in character-speech integration for typical and dyslexic children.

Reading-Related Brain Changes in Audiovisual Processing: Cross-Sectional and Longitudinal MEG Evidence

The ability to establish associations between visual objects and speech sounds is essential for human reading. Understanding the neural adjustments required for acquisition of these arbitrary audiovisual associations can shed light on fundamental reading mechanisms and help reveal how literacy builds on pre-existing brain circuits. To address these questions, the present longitudinal and cross-sectional MEG studies characterize the temporal and spatial neural correlates of audiovisual syllable congruency in children (age range, 4-9 years; 22 males and 20 females) learning to read. Both studies showed that during the first years of reading instruction children gradually set up audiovisual correspondences between letters and speech sounds, which can be detected within the first 400 ms of a bimodal presentation and recruit the superior portions of the left temporal cortex. These findings suggest that children progressively change the way they treat audiovisual syllables as a function of their reading experience. This reading-specific brain plasticity implies (partial) recruitment of pre-existing brain circuits for audiovisual analysis.SIGNIFICANCE STATEMENT Linking visual and auditory linguistic representations is the basis for the development of efficient reading, while dysfunctional audiovisual letter processing predicts future reading disorders. Our developmental MEG project included a longitudinal and a cross-sectional study; both studies showed that children's audiovisual brain circuits progressively change as a function of reading experience. They also revealed an exceptional degree of neuroplasticity in audiovisual neural networks, showing that as children develop literacy, the brain progressively adapts so as to better detect new correspondences between letters and speech sounds.

Multisensory Integration as a Window into Orderly and Disrupted Cognition and Communication

During our everyday lives, we are confronted with a vast amount of information from several sensory modalities. This multisensory information needs to be appropriately integrated for us to effectively engage with and learn from our world. Research carried out over the last half century has provided new insights into the way such multisensory processing improves human performance and perception; the neurophysiological foundations of multisensory function; the time course for its development; how multisensory abilities differ in clinical populations; and, most recently, the links between multisensory processing and cognitive abilities. This review summarizes the extant literature on multisensory function in typical and atypical circumstances, discusses the implications of the work carried out to date for theory and research, and points toward next steps for advancing the field.

Impairments of multisensory integration and cross-sensory learning as pathways to dyslexia

Two sensory systems are intrinsic to learning to read. Written words enter the brain through the visual system and associated sounds through the auditory system. The task before the beginning reader is quite basic. She must learn correspondences between orthographic tokens and phonemic utterances, and she must do this to the point that there is seamless automatic 'connection' between these sensorially distinct units of language. It is self-evident then that learning to read requires formation of cross-sensory associations to the point that deeply encoded multisensory representations are attained. While the majority of individuals manage this task to a high degree of expertise, some struggle to attain even rudimentary capabilities. Why do dyslexic individuals, who learn well in myriad other domains, fail at this particular task? Here, we examine the literature as it pertains to multisensory processing in dyslexia. We find substantial support for multisensory deficits in dyslexia, and make the case that to fully understand its neurological basis, it will be necessary to thoroughly probe the integrity of auditory-visual integration mechanisms.

Rapid extraction of lexical tone phonology in Chinese characters: a visual mismatch negativity study

Background

In alphabetic languages, emerging evidence from behavioral and neuroimaging studies shows the rapid and automatic activation of phonological information in visual word recognition. In the mapping from orthography to phonology, unlike most alphabetic languages in which there is a natural correspondence between the visual and phonological forms, in logographic Chinese, the mapping between visual and phonological forms is rather arbitrary and depends on learning and experience. The issue of whether the phonological information is rapidly and automatically extracted in Chinese characters by the brain has not yet been thoroughly addressed.

Methodology/Principal Findings

We continuously presented Chinese characters differing in orthography and meaning to adult native Mandarin Chinese speakers to construct a constant varying visual stream. In the stream, most stimuli were homophones of Chinese characters: The phonological features embedded in these visual characters were the same, including consonants, vowels and the lexical tone. Occasionally, the rule of phonology was randomly violated by characters whose phonological features differed in the lexical tone.

Conclusions/Significance

We showed that the violation of the lexical tone phonology evoked an early, robust visual response, as revealed by whole-head electrical recordings of the visual mismatch negativity (vMMN), indicating the rapid extraction of phonological information embedded in Chinese characters. Source analysis revealed that the vMMN was involved in neural activations of the visual cortex, suggesting that the visual sensory memory is sensitive to phonological information embedded in visual words at an early processing stage.

Graphophonological processes in dyslexic readers of French: a longitudinal study of the explicitness effect of tasks

Given the well-acknowledged phonological deficit found in dyslexic children, this study was aimed at investigating graphophonological processes in dyslexic readers of French over a 1-year period. Among the different types of phonological processing can be distinguished those related to phonological awareness based on knowledge of the oral language and graphophonological processes based on correspondences between the oral and the written language. In this study, we evaluated graphophonemic and graphosyllabic processes using, in each case, two different tasks varying in the degree of cognitive constraint associated with the task (CC- vs CC+). Twenty 11 year-old dyslexic students were compared with younger normal-readers of the same reading level (RA, n=26) and to normal-readers of the same age (CA, n=24). Two variables were considered in the analyses: accuracy and response latency. Results show that dyslexic readers do process written items at the graphophonological level. Also, results indicate main effects of task (CC- vs CC+), time (T1 vs T2), and group (DYS vs RA vs CA). In general, dyslexic participants' performances are comparable to those of RA and differ from those of CA.

Is there a causal link from a phonological awareness deficit to reading failure in children at familial risk for dyslexia?

The knowledge that reading and phonological awareness are mainly reciprocally related has hardly influenced the status of a phonological awareness deficit as the main cause of a reading deficit in dyslexia. Because direct proofs for this theory are still lacking we investigated children at familial risk for dyslexia in kindergarten and first grade. The familial risk was genuine; 40% developed reading deficits in first grade. However, we did not find any relationship between a phonological awareness or other phonological processing deficits in kindergarten and reading deficits in first grade. Finally, we did not find evidence for the claim that a phonological awareness deficit assumedly causes a reading deficit via 'unstable' or otherwise corrupted letter-speech sound associations. Although earlier research indicated letter knowledge as another significant determinant of later reading deficits, we found no support for this claim. Letter knowledge learning and learning to associate and integrate letters and speech sound are different processes and only problems in the latter process seem directly linked to the development of a reading deficit. The nature of this deficit and the impact it might have on multisensory processing in the whole reading network presents a major challenge to future reading and dyslexia research.

Eye movements in German-speaking children with and without dyslexia when reading aloud

PURPOSE

The phonological difficulty and orthographic regularity of a language influence reading strategies. Only a few studies have been conducted in readers of German, which has a high grapheme-phoneme correspondence. The aim of this study was to investigate, firstly, the influence of different levels of phonological difficulty of reading material in German on reading in children and, secondly, to compare the reading strategies of German children with findings in English-speaking readers.

METHODS

  Eye movements in 16 German children with dyslexia and 16 age-matched control children (mean age 9.5±0.35years) in the third and fourth grades of school were recorded by scanning laser ophthalmoscope while they read aloud two texts of differing levels of difficulty.

RESULTS

  In the dyslexia group, reading speed was slowed, and the number of saccades and regressions was raised markedly, although the percentage of regressions only slightly. The number of eye movements increased in both groups with increasing text difficulty, although much more in the dyslexia group than in the control group, whereas fixation duration was not influenced.

CONCLUSIONS

  Phonological difficulty influences reading speed and eye movement pattern: children with dyslexia markedly increase their number of eye movements and analyse the text in smaller units per fixation, but keep fixation duration constant. This strategy reflects their favouring of the indirect, sublexical route of grapheme-phoneme conversion, whereas readers of English-language texts are more likely to prefer the whole-word approach, i.e. the direct, lexical route that is associated with orthographic memory.

The Long Road to Automation: Neurocognitive Development of Letter–Speech Sound Processing

In transparent alphabetic languages, the expected standard for complete acquisition of letter–speech sound associations is within one year of reading instruction. The neural mechanisms underlying the acquisition of letter–speech sound associations have, however, hardly been investigated. The present article describes an ERP study with beginner and advanced readers in which the influence of letters on speech sound processing is investigated by comparing the MMN to speech sounds presented in isolation with the MMN to speech sounds accompanied by letters. Furthermore, SOA between letter and speech sound presentation was manipulated in order to investigate the development of the temporal window of integration for letter–speech sound processing. Beginner readers, despite one year of reading instruction, showed no early letter–speech sound integration, that is, no influence of the letter on the evocation of the MMN to the speech sound. Only later in the difference wave, at 650 msec, was an influence of the letter on speech sound processing revealed. Advanced readers, with 4 years of reading instruction, showed early and automatic letter–speech sound processing as revealed by an enhancement of the MMN amplitude, however, at a different temporal window of integration in comparison with experienced adult readers. The present results indicate a transition from mere association in beginner readers to more automatic, but still not “adult-like,” integration in advanced readers. In contrast to general assumptions, the present study provides evidence for an extended development of letter–speech sound integration.