Orthographic dependency in the neural correlates of reading: evidence from audiovisual integration in English readers.

Reading skills are indispensible in modern technological societies. In transparent alphabetic orthographies, such as Dutch, reading skills build on associations between letters and speech sounds (LS pairs). Previously, we showed that the superior temporal cortex (STC) of Dutch readers is sensitive to the congruency of LS pairs. Here, we used functional magnetic resonance imaging to investigate whether a similar congruency sensitivity exists in STC of readers of the more opaque English orthography, where the relation among LS pairs is less reliable. Eighteen subjects passively perceived congruent and incongruent audiovisual pairs of different levels of transparency in English: letters and speech sounds (LS; irregular), letters and letter names (LN; fairly transparent), and numerals and number names (NN; transparent). In STC, we found congruency effects for NN and LN, but no effects in the predicted direction (congruent > incongruent) for LS pairs. These findings contrast with previous results obtained from Dutch readers. These data indicate that, through education, the STC becomes tuned to the congruency of transparent audiovisual pairs, but suggests a different neural processing of irregular mappings. The orthographic dependency of LS integration underscores cross-linguistic differences in the neural basis of reading and potentially has important implications for dyslexia interventions across languages.

Numerical predictors of arithmetic success in grades 1-6.

Math relies on mastery and integration of a wide range of simpler numerical processes and concepts. Recent work has identified several numerical competencies that predict variation in math ability. We examined the unique relations between eight basic numerical skills and early arithmetic ability in a large sample (N = 1391) of children across grades 1-6. In grades 1-2, children's ability to judge the relative magnitude of numerical symbols was most predictive of early arithmetic skills. The unique contribution of children's ability to assess ordinality in numerical symbols steadily increased across grades, overtaking all other predictors by grade 6. We found no evidence that children's ability to judge the relative magnitude of approximate, nonsymbolic numbers was uniquely predictive of arithmetic ability at any grade. Overall, symbolic number processing was more predictive of arithmetic ability than nonsymbolic number processing, though the relative importance of symbolic number ability appears to shift from cardinal to ordinal processing.

What basic number processing measures in kindergarten explain unique variability in first-grade arithmetic proficiency?

Relations between children's mathematics achievement and their basic number processing skills have been reported in both cross-sectional and longitudinal studies. Yet, some key questions are currently unresolved, including which kindergarten skills uniquely predict children's arithmetic fluency during the first year of formal schooling and the degree to which predictors are contingent on children's level of arithmetic proficiency. The current study assessed kindergarteners' non-symbolic and symbolic number processing efficiency. In addition, the contribution of children's underlying magnitude representations to differences in arithmetic achievement was assessed. Subsequently, in January of Grade 1, their arithmetic proficiency was assessed. Hierarchical regression analysis revealed that children's efficiency to compare digits, count, and estimate numerosities uniquely predicted arithmetic differences above and beyond the non-numerical factors included. Moreover, quantile regression analysis indicated that symbolic number processing efficiency was consistently a significant predictor of arithmetic achievement scores regardless of children's level of arithmetic proficiency, whereas their non-symbolic number processing efficiency was not. Finally, none of the task-specific effects indexing children's representational precision was significantly associated with arithmetic fluency. The implications of the results are 2-fold. First, the findings indicate that children's efficiency to process symbols is important for the development of their arithmetic fluency in Grade 1 above and beyond the influence of non-numerical factors. Second, the impact of children's non-symbolic number processing skills does not depend on their arithmetic achievement level given that they are selected from a nonclinical population.

Predictors of developmental dyslexia in European orthographies with varying complexity.

BACKGROUND: The relationship between phoneme awareness, rapid automatized naming (RAN), verbal short-term/working memory (ST/WM) and diagnostic category is investigated in control and dyslexic children, and the extent to which this depends on orthographic complexity. METHODS: General cognitive, phonological and literacy skills were tested in 1,138 control and 1,114 dyslexic children speaking six different languages spanning a large range of orthographic complexity (Finnish, Hungarian, German, Dutch, French, English). RESULTS: Phoneme deletion and RAN were strong concurrent predictors of developmental dyslexia, while verbal ST/WM and general verbal abilities played a comparatively minor role. In logistic regression models, more participants were classified correctly when orthography was more complex. The impact of phoneme deletion and RAN-digits was stronger in complex than in less complex orthographies. CONCLUSIONS: Findings are largely consistent with the literature on predictors of dyslexia and literacy skills, while uniquely demonstrating how orthographic complexity exacerbates some symptoms of dyslexia.

The neural signature of orthographic-phonological binding in successful and failing reading development.

Learning to read in alphabetic orthographies starts with learning a script code consisting of letter-speech sound pairs. Although children know which letters belong to which speech sounds within months, it takes much longer to automatically integrate them into newly constructed audiovisual objects. This extended learning process corresponds with observations that reliable letter and word specific activations in the fusiform cortex also occur relatively late in reading development. The present review discusses electrophysiological and neuroimaging studies of the nature and mechanisms involved in letter-speech sound integration in normal and dyslexic readers. It is demonstrated that letter-speech sound associations do not develop in parallel with visual letter recognition but immediately work in concert to form orthographic-phonological bonds which remain active even in experienced reading. Effective letter-speech sound integration may be necessary for reliable letter recognition to develop. In contrast, it is this basic integration of letters and speech sounds which poses an immediate problem for beginning dyslexic readers, and remains problematic in adult dyslexic readers. It is hypothesized that a specific orthographic-phonological binding deficit may not only act as a proximal cause for reading deficits in dyslexia, but may also explain the notorious lack of reading fluency. Finally, it is suggested that similar integrated audiovisual representations may also exist for larger grain-sizes in the same posterior occipitotemporal/inferoparietal network as identified for orthographic-phonological integration of letters and speech sounds.

Evidence for a specific cross-modal association deficit in dyslexia: an electrophysiological study of letter-speech sound processing.

The phonological deficit theory of dyslexia assumes that degraded speech sound representations might hamper the acquisition of stable letter-speech sound associations necessary for learning to read. However, there is only scarce and mainly indirect evidence for this assumed letter-speech sound association problem. The present study aimed at clarifying the nature and the role of letter-speech sound association problems in dyslexia by analysing event-related potentials (ERP) of 11-year-old dyslexic children to speech sounds in isolation or combined with letters, which were presented either simultaneously with or 200 ms before the speech sounds. Recent studies with normal readers revealed that letters systematically modulated speech sound processing in an early (mismatch negativity or MMN) and late (Late Discriminatory Negativity or LDN) time-window. The amplitude of the MMN and LDN to speech sounds was enhanced when speech sounds were presented with letters. The dyslexic readers in the present study, however, did not exhibit any early influences of letters on speech sounds even after 4 years of reading instruction, indicating no automatic integration of letters and speech sounds. Interestingly, they revealed a systematic late effect of letters on speech sound processing, probably reflecting the mere association of letters and speech sounds. This pattern is strongly divergent from that observed in age-matched normal readers, who showed both early and late effects, but reminiscent of that observed in beginner normal readers in a previous study (Froyen, Bonte, van Atteveldt & Blomert, 2009). The finding that the quality of letter-speech sound processing is directly related to reading fluency urges further research into the role of audiovisual integration in the development of reading failure in dyslexia.

Deviant processing of letters and speech sounds as proximate cause of reading failure: a functional magnetic resonance imaging study of dyslexic children.

Learning to associate auditory information of speech sounds with visual information of letters is a first and critical step for becoming a skilled reader in alphabetic languages. Nevertheless, it remains largely unknown which brain areas subserve the learning and automation of such associations. Here, we employ functional magnetic resonance imaging to study letter-speech sound integration in children with and without developmental dyslexia. The results demonstrate that dyslexic children show reduced neural integration of letters and speech sounds in the planum temporale/Heschl sulcus and the superior temporal sulcus. While cortical responses to speech sounds in fluent readers were modulated by letter-speech sound congruency with strong suppression effects for incongruent letters, no such modulation was observed in the dyslexic readers. Whole-brain analyses of unisensory visual and auditory group differences additionally revealed reduced unisensory responses to letters in the fusiform gyrus in dyslexic children, as well as reduced activity for processing speech sounds in the anterior superior temporal gyrus, planum temporale/Heschl sulcus and superior temporal sulcus. Importantly, the neural integration of letters and speech sounds in the planum temporale/Heschl sulcus and the neural response to letters in the fusiform gyrus explained almost 40% of the variance in individual reading performance. These findings indicate that an interrelated network of visual, auditory and heteromodal brain areas contributes to the skilled use of letter-speech sound associations necessary for learning to read. By extending similar findings in adults, the data furthermore argue against the notion that reduced neural integration of letters and speech sounds in dyslexia reflect the consequence of a lifetime of reading struggle. Instead, they support the view that letter-speech sound integration is an emergent property of learning to read that develops inadequately in dyslexic readers, presumably as a result of a deviant interactive specialization of neural systems for processing auditory and visual linguistic inputs.

fMR-adaptation indicates selectivity to audiovisual content congruency in distributed clusters in human superior temporal cortex.

BACKGROUND: Efficient multisensory integration is of vital importance for adequate interaction with the environment. In addition to basic binding cues like temporal and spatial coherence, meaningful multisensory information is also bound together by content-based associations. Many functional Magnetic Resonance Imaging (fMRI) studies propose the (posterior) superior temporal cortex (STC) as the key structure for integrating meaningful multisensory information. However, a still unanswered question is how superior temporal cortex encodes content-based associations, especially in light of inconsistent results from studies comparing brain activation to semantically matching (congruent) versus nonmatching (incongruent) multisensory inputs. Here, we used fMR-adaptation (fMR-A) in order to circumvent potential problems with standard fMRI approaches, including spatial averaging and amplitude saturation confounds. We presented repetitions of audiovisual stimuli (letter-speech sound pairs) and manipulated the associative relation between the auditory and visual inputs (congruent/incongruent pairs). We predicted that if multisensory neuronal populations exist in STC and encode audiovisual content relatedness, adaptation should be affected by the manipulated audiovisual relation. RESULTS: The results revealed an occipital-temporal network that adapted independently of the audiovisual relation. Interestingly, several smaller clusters distributed over superior temporal cortex within that network, adapted stronger to congruent than to incongruent audiovisual repetitions, indicating sensitivity to content congruency. CONCLUSIONS: These results suggest that the revealed clusters contain multisensory neuronal populations that encode content relatedness by selectively responding to congruent audiovisual inputs, since unisensory neuronal populations are assumed to be insensitive to the audiovisual relation. These findings extend our previously revealed mechanism for the integration of letters and speech sounds and demonstrate that fMR-A is sensitive to multisensory congruency effects that may not be revealed in BOLD amplitude per se.

Orthographic depth and its impact on universal predictors of reading: a cross-language investigation.

Alphabetic orthographies differ in the transparency of their letter-sound mappings, with English orthography being less transparent than other alphabetic scripts. The outlier status of English has led scientists to question the generality of findings based on English-language studies. We investigated the role of phonological awareness, memory, vocabulary, rapid naming, and nonverbal intelligence in reading performance across five languages lying at differing positions along a transparency continuum (Finnish, Hungarian, Dutch, Portuguese, and French). Results from a sample of 1,265 children in Grade 2 showed that phonological awareness was the main factor associated with reading performance in each language. However, its impact was modulated by the transparency of the orthography, being stronger in less transparent orthographies. The influence of rapid naming was rather weak and limited to reading and decoding speed. Most predictors of reading performance were relatively universal across these alphabetic languages, although their precise weight varied systematically as a function of script transparency.

Long-term cognitive dynamics of fluent reading development.

Most theories of reading development assume a shift from slow sequential subword decoding to automatic processing of orthographic word forms. We hypothesized that this shift should be reflected in a concomitant shift in reading-related cognitive functions. The current study investigated the cognitive dynamics underlying reading development in a large school sample ranging from beginning to experienced readers. The results showed that phonological awareness (PA) and rapid automatized naming (RAN) contributed substantially to reading fluency over all six primary school grades. However, the relationship between PA and word (but not pseudoword) reading fluency decreased as a function of reading experience, whereas the relationship between RAN and word reading fluency increased gradually. Moreover, this cognitive shift was most pronounced for high-frequency words. The results seem to point to the development of one (and only one) reading network for all types of words in which processing load or type of processing depends on word familiarity and amount of reading experience.

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.

Naming problems do not reflect a second independent core deficit in dyslexia: double deficits explored.

The double deficit hypothesis states that naming speed problems represent a second core deficit in dyslexia independent from a phonological deficit. The current study investigated the main assumptions of this hypothesis in a large sample of well-diagnosed dyslexics. The three main findings were that (a) naming speed was consistently related only to reading speed; (b) phonological processing speed and naming speed loaded on the same factor, and this factor contributed strongly to reading speed; and (c) although general processing speed was involved in speeded naming of visual items, it did not explain the relationship between naming speed and reading speed. The results do not provide support for the existence of a second independent core naming deficit in dyslexia and indicate that speeded naming tasks are mainly phonological processing speed tasks with an important addition: fast cross-modal matching of visual symbols and phonological codes.

Integration of letters and speech sounds in the human brain.

Most people acquire literacy skills with remarkable ease, even though the human brain is not evolutionarily adapted to this relatively new cultural phenomenon. Associations between letters and speech sounds form the basis of reading in alphabetic scripts. We investigated the functional neuroanatomy of the integration of letters and speech sounds using functional magnetic resonance imaging (fMRI). Letters and speech sounds were presented unimodally and bimodally in congruent or incongruent combinations. Analysis of single-subject data and group data aligned on the basis of individual cortical anatomy revealed that letters and speech sounds are integrated in heteromodal superior temporal cortex. Interestingly, responses to speech sounds in a modality-specific region of the early auditory cortex were modified by simultaneously presented letters. These results suggest that efficient processing of culturally defined associations between letters and speech sounds relies on neural mechanisms similar to those naturally evolved for integrating audiovisual speech.

Task-irrelevant visual letters interact with the processing of speech sounds in heteromodal and unimodal cortex.

Letters and speech sounds are the basic units of correspondence between spoken and written language. Associating auditory information of speech sounds with visual information of letters is critical for learning to read; however, the neural mechanisms underlying this association remain poorly understood. The present functional magnetic resonance imaging study investigates the automaticity and behavioral relevance of integrating letters and speech sounds. Within a unimodal auditory identification task, speech sounds were presented in isolation (unimodally) or bimodally in congruent and incongruent combinations with visual letters. Furthermore, the quality of the visual letters was manipulated parametrically. Our analyses revealed that the presentation of congruent visual letters led to a behavioral improvement in identifying speech sounds, which was paralleled by a similar modulation of cortical responses in the left superior temporal sulcus. Under low visual noise, cortical responses in superior temporal and occipito-temporal cortex were further modulated by the congruency between auditory and visual stimuli. These cross-modal modulations of performance and cortical responses during an unimodal auditory task (speech identification) indicate the existence of a strong and automatic functional coupling between processing of letters (orthography) and speech (phonology) in the literate adult brain.

Cross-modal enhancement of the MMN to speech-sounds indicates early and automatic integration of letters and speech-sounds.

Recently brain imaging evidence indicated that letter/speech-sound integration, necessary for establishing fluent reading, takes place in auditory association areas and that the integration is influenced by stimulus onset asynchrony (SOA) between the letter and the speech-sound. In the present study, we used a specific ERP measure known for its automatic character, the mismatch negativity (MMN), to investigate the time course and automaticity of letter/speech-sound integration. We studied the effect of visual letters and SOA on the MMN elicited by a deviant speech-sound. We found a clear enhancement of the MMN by simultaneously presenting a letter, but without changing the auditory stimulation. This enhancement diminishes linearly with increasing SOA. These results suggest that letters and speech-sounds are processed as compound stimuli early and automatically in the auditory association cortex of fluent readers and that this processing is strongly dependent on timing.

Atypical White Matter Connectivity in Dyslexic Readers of a Fairly Transparent Orthography.

Atypical structural properties of the brain's white matter bundles have been associated with failing reading acquisition in developmental dyslexia. Because these white matter properties may show dynamic changes with age and orthographic depth, we examined fractional anisotropy (FA) along 16 white matter tracts in 8- to 11-year-old dyslexic (DR) and typically reading (TR) children learning to read in a fairly transparent orthography (Dutch). Our results showed higher FA values in the bilateral anterior thalamic radiations of DRs and FA values of the left thalamic radiation scaled with behavioral reading-related scores. Furthermore, DRs tended to have atypical FA values in the bilateral arcuate fasciculi. Children's age additionally predicted FA values along the tracts. Together, our findings suggest differential contributions of cortical and thalamo-cortical pathways to the developing reading network in dyslexic and typical readers, possibly indicating prolonged letter-by-letter reading or increased attentional and/or working memory demands in dyslexic children during reading.

Deviant neurophysiological responses to phonological regularities in speech in dyslexic children.

Developmental dyslexia is strongly associated with a phonological deficit. Yet, implicit phonological processing (in)capacities in dyslexia remain relatively unexplored. Here we use a neurophysiological response sensitive to experience-dependent auditory memory traces, the mismatch negativity (MMN), to investigate implicit phonological processing of natural speech in dyslexic and normally reading children. In a modified passive oddball design that minimizes the contribution of acoustic processes, we presented non-words that differed by the degree of phonotactic probability, i.e. the distributional frequency of phoneme combinations in a given language. Overall morphology of ERP responses to the non-words indicated comparable processing of acoustic-phonetic stimulus differences in both children groups. Consistent with previous findings in adults, normally reading children showed a significantly stronger MMN response to the non-word with high phonotactic probability (notsel) as compared to the non-word with low phonotactic probability (notkel), suggesting auditory cortical tuning to statistical regularities of phoneme combinations. In contrast, dyslexic children did not show this sensitivity to phonotactic probability. These findings indicate that the phonological problems often reported in dyslexia relate to a subtle deficit in the implicit phonetic-phonological processing of natural speech.

Altered patterns of directed connectivity within the reading network of dyslexic children and their relation to reading dysfluency.

Reading is a complex cognitive skill subserved by a distributed network of visual and language-related regions. Disruptions of connectivity within this network have been associated with developmental dyslexia but their relation to individual differences in the severity of reading problems remains unclear. Here we investigate whether dysfunctional connectivity scales with the level of reading dysfluency by examining EEG recordings during visual word and false font processing in 9-year-old typically reading children (TR) and two groups of dyslexic children: severely dysfluent (SDD) and moderately dysfluent (MDD) dyslexics. Results indicated weaker occipital to inferior-temporal connectivity for words in both dyslexic groups relative to TRs. Furthermore, SDDs exhibited stronger connectivity from left central to right inferior-temporal and occipital sites for words relative to TRs, and for false fonts relative to both MDDs and TRs. Importantly, reading fluency was positively related with forward and negatively with backward connectivity. Our results suggest disrupted visual processing of words in both dyslexic groups, together with a compensatory recruitment of right posterior brain regions especially in the SDDs during word and false font processing. Functional connectivity in the brain's reading network may thus depend on the level of reading dysfluency beyond group differences between dyslexic and typical readers.

The recognition of phonologically assimilated words does not depend on specific language experience.

In a series of 5 experiments, we investigated whether the processing of phonologically assimilated utterances is influenced by language learning. Previous experiments had shown that phonological assimilations, such as /lean#bacon/ → [leam bacon], are compensated for in perception. In this article, we investigated whether compensation for assimilation can occur without experience with an assimilation rule using automatic event-related potentials. Our first experiment indicated that Dutch listeners compensate for a Hungarian assimilation rule. Two subsequent experiments, however, failed to show compensation for assimilation by both Dutch and Hungarian listeners. Two additional experiments showed that this was due to the acoustic properties of the assimilated utterance, confirming earlier reports that phonetic detail is important in compensation for assimilation. Our data indicate that compensation for assimilation can occur without experience with an assimilation rule, in line with phonetic-phonological theories that assume that speech production is influenced by speech-perception abilities.

Cognitive and familial risk evidence converged: A data-driven identification of distinct and homogeneous subtypes within the heterogeneous sample of reading disabled children.

The evident degree of heterogeneity observed in reading disabled children has puzzled reading researchers for decades. Recent advances in the genetic underpinnings of reading disability have indicated that the heritable, familial risk for dyslexia is a major risk factor. The present data-driven, classification attempt aims to revisit the possibility of identifying distinct cognitive deficit profiles in a large sample of second to fourth grade reading disabled children. In this sample, we investigated whether genetic and environmental risk factors are able to distinguish between poor reader subtypes. In this profile, we included reading-related measures of phonemic awareness, letter-speech sound processing and rapid naming, known as candidate vulnerability markers associated with dyslexia and familial risk for dyslexia, as well as general cognitive abilities (non-verbal IQ and vocabulary). Clustering was based on a 200 multi-start K-means approach. Results revealed four emerging subtypes of which the first subtype showed no cognitive deficits underlying their poor reading skills (Reading-only impaired poor readers). The other three subtypes shared a core phonological deficit (PA) with a variable and discriminative expression across the other underlying vulnerability markers. More specific, type 2 showed low to poor performance across all reading-related and general cognitive abilities (general poor readers), type 3 showed a specific letter-speech sound mapping deficit next to a PA deficit (PA-LS specific poor readers) and type 4 showed a specific rapid naming deficit complementing their phonological weakness (PA-RAN specific poor readers). The first three poor reader profiles were more characterized by variable environmental risk factor, while the fourth, PA-RAN poor reader subtype showed a significantly strong familial risk for dyslexia. Overall, when we zoom in on the heterogeneous phenomenon of reading disability, unique and distinct cognitive subtypes can be identified, distinguishing between those poor readers more influences by the role of genes and those more influenced by environmental risk factors. Taking into account this diversity of distinct cognitive subtypes, instead of looking at the reading disabled sample as a whole, will help tailor future diagnostic and intervention efforts more specifically to the needs of children with such a specific deficit and risk pattern, as well as providing a more promising way forward for genetic studies of dyslexia.