How does learning to read affect speech perception?

Beyond the Visual Word Form Area - a cognitive characterization of the left ventral occipitotemporal cortex

The left ventral occipitotemporal cortex has been traditionally viewed as a pathway for visual object recognition including written letters and words. Its crucial role in reading was strengthened by the studies on the functionally localized "Visual Word Form Area" responsible for processing word-like information. However, in the past 20 years, empirical studies have challenged the assumptions of this brain region as processing exclusively visual or even orthographic stimuli. In this review, we aimed to present the development of understanding of the left ventral occipitotemporal cortex from the visually based letter area to the modality-independent symbolic language related region. We discuss theoretical and empirical research that includes orthographic, phonological, and semantic properties of language. Existing results showed that involvement of the left ventral occipitotemporal cortex is not limited to unimodal activity but also includes multimodal processes. The idea of the integrative nature of this region is supported by the broad functional and structural connectivity with language-related and attentional brain networks. We conclude that although the function of the area is not yet fully understood in human cognition, its role goes beyond visual word form processing. The left ventral occipitotemporal cortex seems to be crucial for combining higher-level language information with abstract forms that convey meaning independently of modality.

A single case neuroimaging study of tickertape synesthesia

Reading acquisition is enabled by deep changes in the brain's visual system and language areas, and in the links subtending their collaboration. Disruption of those plastic processes commonly results in developmental dyslexia. However, atypical development of reading mechanisms may occasionally result in ticker-tape synesthesia (TTS), a condition described by Francis Galton in 1883 wherein individuals "see mentally in print every word that is uttered (…) as from a long imaginary strip of paper". While reading is the bottom-up translation of letters into speech, TTS may be viewed as its opposite, the top-down translation of speech into internally visualized letters. In a series of functional MRI experiments, we studied MK, a man with TTS. We showed that a set of left-hemispheric areas were more active in MK than in controls during the perception of normal than reversed speech, including frontoparietal areas involved in speech processing, and the Visual Word Form Area, an occipitotemporal region subtending orthography. Those areas were identical to those involved in reading, supporting the construal of TTS as upended reading. Using dynamic causal modeling, we further showed that, parallel to reading, TTS induced by spoken words and pseudowords relied on top-down flow of information along distinct lexical and phonological routes, involving the middle temporal and supramarginal gyri, respectively. Future studies of TTS should shed new light on the neurodevelopmental mechanisms of reading acquisition, their variability and their disorders.

The Impact of Transcranial Magnetic Stimulation on Reading Processes: A Systematic Review

The current systematic review examines the behavioral effects of TMS on reading. Transcranial magnetic stimulation (TMS) to targeted nodes of the brain's reading network has been shown to impact reading. Extracted data included (a) study characteristics, (b) methodology, (c) targeted nodes, (d) control paradigm, (e) type of reading task, (f) adverse effects, and (g) main findings. Data was classified by type of reading task: 1) phonological processing, 2) semantic judgment, 3) lexical decision, 4) whole word reading, and 5) visual or text characteristics. Seventy records from 46 studies (n = 844) were identified. Results indicate that TMS modulates semantic judgments when focused in the anterior aspects of the reading circuit, phonological processes after stimulation within the dorsal circuit, and impacts single word recognition and contextual reading when administered to the ventral circuit. Findings suggest that changes in specific behavioral aspects of reading following TMS may contribute to identification of foci for use as part of reading interventions.

Subtitled speech: Phenomenology of tickertape synesthesia

With effort, most literate persons can conjure more or less vague visual mental images of the written form of words they are hearing, an ability afforded by the links between sounds, meaning, and letters. However, as first reported by Francis Galton, persons with ticker-tape synesthesia (TTS) automatically perceive in their mind's eye accurate and vivid images of the written form of all utterances which they are hearing. We propose that TTS results from an atypical setup of the brain reading system, with an increased top-down influence of phonology on orthography. As a first descriptive step towards a deeper understanding of TTS, we identified 26 persons with TTS. Participants had to answer to a questionnaire aiming to describe the phenomenology of TTS along multiple dimensions, including visual and temporal features, triggering stimuli, voluntary control, interference with language processing, etc. We also assessed the synesthetic percepts elicited experimentally by auditory stimuli such as non-speech sounds, pseudowords, and words with various types of correspondence between sounds and letters. We discuss the potential cerebral substrates of those features, argue that TTS may provide a unique window in the mechanisms of written language processing and acquisition, and propose an agenda for future research.

Correspondence between cognitive and neural representations for phonology, orthography, and semantics in supramarginal compared to angular gyrus

The angular and supramarginal gyri (AG and SMG) together constitute the inferior parietal lobule (IPL) and have been associated with cognitive functions that support reading. How those functions are distributed across the AG and SMG is a matter of debate, the resolution of which is hampered by inconsistencies across stereotactic atlases provided by the major brain image analysis software packages. Schematic results from automated meta-analyses suggest primarily semantic (word meaning) processing in the left AG, with more spatial overlap among phonological (auditory word form), orthographic (visual word form), and semantic processing in the left SMG. To systematically test for correspondence between patterns of neural activation and phonological, orthographic, and semantic representations, we re-analyze a functional magnetic resonance imaging data set of participants reading aloud 465 words. Using representational similarity analysis, we test the hypothesis that within cytoarchitecture-defined subregions of the IPL, phonological representations are primarily associated with the SMG, while semantic representations are primarily associated with the AG. To the extent that orthographic representations can be de-correlated from phonological representations, they will be associated with cortex peripheral to the IPL, such as the intraparietal sulcus. Results largely confirmed these hypotheses, with some nuanced exceptions, which we discuss in terms of neurally inspired computational cognitive models of reading that learn mappings among distributed representations for orthography, phonology, and semantics. De-correlating constituent representations making up complex cognitive processes, such as reading, by careful selection of stimuli, representational formats, and analysis techniques, are promising approaches for bringing additional clarity to brain structure-function relationships.

Neuromodulatory effects of transcranial magnetic stimulation on language performance in healthy participants: Systematic review and meta-analysis

Background

The causal relationships between neural substrates and human language have been investigated by transcranial magnetic stimulation (TMS). However, the robustness of TMS neuromodulatory effects is still largely unspecified. This study aims to systematically examine the efficacy of TMS on healthy participants' language performance.

Methods

For this meta-analysis, we searched PubMed, Web of Science, PsycINFO, Scopus, and Google Scholar from database inception until October 15, 2022 for eligible TMS studies on language comprehension and production in healthy adults published in English. The quality of the included studies was assessed with the Cochrane risk of bias tool. Potential publication biases were assessed by funnel plots and the Egger Test. We conducted overall as well as moderator meta-analyses. Effect sizes were estimated using Hedges'g (g) and entered into a three-level random effects model.

Results

Thirty-seven studies (797 participants) with 77 effect sizes were included. The three-level random effects model revealed significant overall TMS effects on language performance in healthy participants (RT: g = 0.16, 95% CI: 0.04-0.29; ACC: g = 0.14, 95% CI: 0.04-0.24). Further moderator analyses indicated that (a) for language tasks, TMS induced significant neuromodulatory effects on semantic and phonological tasks, but didn't show significance for syntactic tasks; (b) for cortical targets, TMS effects were not significant in left frontal, temporal or parietal regions, but were marginally significant in the inferior frontal gyrus in a finer-scale analysis; (c) for stimulation parameters, stimulation sites extracted from previous studies, rTMS, and intensities calibrated to the individual resting motor threshold are more prone to induce robust TMS effects. As for stimulation frequencies and timing, both high and low frequencies, online and offline stimulation elicited significant effects; (d) for experimental designs, studies adopting sham TMS or no TMS as the control condition and within-subject design obtained more significant effects.

Discussion

Overall, the results show that TMS may robustly modulate healthy adults' language performance and scrutinize the brain-and-language relation in a profound fashion. However, due to limited sample size and constraints in the current meta-analysis approach, analyses at a more comprehensive level were not conducted and results need to be confirmed by future studies.

Systematic review registration

[https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=366481], identifier [CRD42022366481].

The effects of alphabetic literacy, linguistic-processing demand and tone type on the dichotic listening of lexical tones

Brain lateralization of lexical tone processing remains a matter of debate. In this study we used a dichotic listening paradigm to examine the influences of the knowledge of Jyutping (a romanization writing system which provides explicit Cantonese tone markers), linguistic-processing demand and tone type on the ear preference pattern of native tone processing in Hong Kong Cantonese speakers. While participants with little knowledge of Jyutping showed a previously reported left-ear advantage (LEA), those with a good level of Jyutping expertise exhibited either a right-ear advantage or bilateral processing during lexical tone identification and contour tone discrimination, respectively. As for the effect of linguistic-processing demand, while an LEA was found in acoustic/phonetic perception situations, this advantage disappeared and was replaced by a bilateral pattern in conditions that involved a greater extent of linguistic processing, suggesting an increased involvement of the left hemisphere. Regarding the effect of tone type, both groups showed an LEA in level tone discrimination, but only the Jyutping group demonstrated a bilateral pattern in contour tone discrimination. Overall, knowledge of written codes of tones, greater degree of linguistic processing and contour tone processing seem to influence the brain lateralization of lexical tone processing in native listeners of Cantonese by increasing the recruitment of the left-hemisphere language network.

Neural correlates of phonology-to-orthography mapping consistency effects on Chinese spoken word recognition

Previous studies have shown that reading experience reshapes speech processing. The orthography can be implemented in the brain by restructuring the phonological representations or being co-activated during spoken word recognition. This study utilized event-related functional magnetic resonance imaging and functional connectivity analysis to examine the neural mechanism underlying two types of orthographic effects in the Chinese auditory semantic category task, namely phonology-to-orthography consistency (POC) and homophone density (HD). We found that the POC effects originated from the speech network, suggesting that sublexical orthographic information could change the organization of preexisting phonological representations when learning to read. Meanwhile, the HD effects were localized to the left fusiform and lingual gyrus, suggesting that lexical orthographic knowledge may be activated online during spoken word recognition. These results demonstrated the different natures and neural mechanisms for the POC and HD effects on Chinese spoken word recognition.

The Effect of Orthographic Transparency on Auditory Word Recognition Across the Development of Reading Proficiency

A question under debate in psycholinguistics is the nature of the relationship between spoken and written languages. Although it has been extensively shown that orthographic transparency, which varies across writing systems, strongly affects reading performance, its role in speech processing is much less investigated. The present study addressed this issue in Persian, whose writing system provides a possibility to assess the impact of orthographic transparency on spoken word recognition in young children at different stages of reading acquisition. In Persian, the long vowels are systematically present in the script, whereas the spelling correspondence of short vowels is progressively omitted from the script in the course of reading acquisition, thus, turning transparent into opaque spelling. Based on this unique characteristic, we tested 144 monolingual Persian-speaking nonreaders (i.e., preschoolers) and readers (second graders to fifth graders and young adults) in an auditory lexical decision task using transparent and opaque words. Overall, the results showed that, in accordance with the fact that the diacritics of short vowels are progressively omitted during the second year of schooling, the stimuli containing short vowels (opaque words) were recognized more slowly than transparent ones in third graders. Interestingly, there is a hint that the emergence of the transparency effect in the third graders was associated with an overall slower recognition speed in this group compared to their younger peers. These findings indicate that learning opaque spelling-sound correspondence might not only generate interference between the two language codes but also induce a general processing cost in the entire spoken language system.

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.

Effect of Cognitive Variables on the Reading Ability of Spanish Children at Age Seven

The objective of this study is to determine the contribution made by knowledge of letters, phonological awareness, phonological memory, and alphanumeric and non-alphanumeric rapid automatized naming at the ages of six and seven to the ability of Spanish children to read words at 7 years of age. A total of 116 Spanish-speaking school children took part in the study, from schools located in an average socio-cultural setting, without special educational needs. The reading ability of these pupils was evaluated at the age of seven, and cognitive variables were assessed at 6 and 7 years of age. Descriptive-exploratory analyses, bivariate analyses, and multivariate regressions were performed. The results show that cognitive variables measured at these ages contribute differently to the ability to read words at 7 years of age. Rapid naming does not seem to influence word reading; knowledge of letters no longer influences word reading as children grow older; and phonological awareness and phonological memory maintain their contribution to the explanation of word reading. These results indicate that reading in Spanish depends on different cognitive variables and that this relationship varies according to age. The findings have key educational implications in terms of teaching reading skills and the prevention of specific learning difficulties in Spanish Primary Education.

Literacy Advantages Beyond Reading: Prediction of Spoken Language

Literacy has many obvious benefits: it exposes the reader to a wealth of new information and enhances syntactic knowledge. However, we argue that literacy has an additional, often overlooked, benefit: it enhances people's ability to predict spoken language thereby aiding comprehension. Readers are under pressure to process information more quickly than listeners and reading provides excellent conditions - in particular, a stable environment - for training the predictive system. It also leads to increased awareness of words as linguistic units and to more fine-grained phonological and additional orthographic representations, which sharpen lexical representations and facilitate the retrieval of predicted representations. Thus, reading trains core processes and representations involved in language prediction that are common to both reading and listening.

The Influence of Orthography on Phonemic Knowledge: An Experimental Investigation on German and Persian

This study investigated whether the phonological representation of a word is modulated by its orthographic representation in case of a mismatch between the two representations. Such a mismatch is found in Persian, where short vowels are represented phonemically but not orthographically. Persian adult literates, Persian adult illiterates, and German adult literates were presented with two auditory tasks, an AX-discrimination task and a reversal task. We assumed that if orthographic representations influence phonological representations, Persian literates should perform worse than Persian illiterates or German literates on items with short vowels in these tasks. The results of the discrimination tasks showed that Persian literates and illiterates as well as German literates were approximately equally competent in discriminating short vowels in Persian words and pseudowords. Persian literates did not well discriminate German words containing phonemes that differed only in vowel length. German literates performed relatively poorly in discriminating German homographic words that differed only in vowel length. Persian illiterates were unable to perform the reversal task in Persian. The results of the other two participant groups in the reversal task showed the predicted poorer performance of Persian literates on Persian items containing short vowels compared to items containing long vowels only. German literates did not show this effect in German. Our results suggest two distinct effects of orthography on phonemic representations: whereas the lack of orthographic representations seems to affect phonemic awareness, homography seems to affect the discriminability of phonemic representations.

Functional hierarchy for tactile processing in the visual cortex of sighted adults

Perception via different sensory modalities was traditionally believed to be supported by largely separate brain systems. However, a growing number of studies demonstrate that the visual cortices of typical, sighted adults are involved in tactile and auditory perceptual processing. Here, we investigated the spatiotemporal dynamics of the visual cortex's involvement in a complex tactile task: Braille letter recognition. Sighted subjects underwent Braille training and then participated in a transcranial magnetic stimulation (TMS) study in which they tactually identified single Braille letters. During this task, TMS was applied to their left early visual cortex, visual word form area (VWFA), and left early somatosensory cortex at five time windows from 20 to 520 ms following the Braille letter presentation's onset. The subjects' response accuracy decreased when TMS was applied to the early visual cortex at the 120-220 ms time window and when TMS was applied to the VWFA at the 320-420 ms time window. Stimulation of the early somatosensory cortex did not have a time-specific effect on the accuracy of the subjects' Braille letter recognition, but rather caused a general slowdown during this task. Our results indicate that the involvement of sighted people's visual cortices in tactile perception respects the canonical visual hierarchy-the early tactile processing stages involve the early visual cortex, whereas more advanced tactile computations involve high-level visual areas. Our findings are compatible with the metamodal account of brain organization and suggest that the whole visual cortex may potentially support spatial perception in a task-specific, sensory-independent manner.

Transfer of sensorimotor learning reveals phoneme representations in preliterate children

Reading acquisition is strongly intertwined with phoneme awareness that relies on implicit phoneme representations. We asked whether phoneme representations emerge before literacy. We recruited two groups of children, 4 to 5-year-old preschoolers (N = 29) and 7 to 8-year-old schoolchildren (N = 24), whose phonological awareness was evaluated, and one adult control group (N = 17). We altered speakers' auditory feedback in real time to elicit persisting pronunciation changes, referred to as auditory-motor adaptation or learning. Assessing the transfer of learning at phoneme level enabled us to investigate the developmental time-course of phoneme representations. Significant transfer at phoneme level occurred in preschoolers, as well as schoolchildren and adults. In addition, we found a relationship between auditory-motor adaptation and phonological awareness in both groups of children. Overall, these results suggest that phoneme representations emerge before literacy acquisition, and that these sensorimotor representations may set the ground for phonological awareness.

Orthographic influence on spoken word identification: Behavioral and fMRI evidence

The current study investigated behavioral and neuroimaging evidence for orthographic influences on auditory word identification. To assess such influences, the proportion of similar sounding words (i.e. phonological neighbors) that were also spelled similarly (i.e., orthographic neighbors) was computed for each auditorily presented word as the Orthographic-to-Phonological Overlap Ratio (OPOR). Speech intelligibility was manipulated by presenting monosyllabic words in multi-talker babble at two signal-to-noise ratios: + 3 and + 10 dB SNR. Identification rates were lower for high overlap words in the challenging + 3 dB SNR condition. In addition, BOLD contrast increased with OPOR at the more difficult SNR, and decreased with OPOR under more favorable SNR conditions. Both voxel-based and region of interest analyses demonstrated robust effects of OPOR in several cingulo-opercular regions. However, contrary to prior theoretical accounts, no task-related activity was observed in posterior regions associated with phonological or orthographic processing. We suggest that, when processing is difficult, orthographic-to-phonological feature overlap increases the availability of competing responses, which then requires additional support from domain general performance systems in order to produce a single response.

Consonant Age-of-Acquisition Effects in Nonword Repetition Are Not Articulatory in Nature

PURPOSE

Most research examining long-term-memory effects on nonword repetition (NWR) has focused on lexical-level variables. Phoneme-level variables have received little attention, although there are reasons to expect significant sublexical effects in NWR. To further understand the underlying processes of NWR, this study examined effects of sublexical long-term phonological knowledge by testing whether performance differs when the stimuli comprise consonants acquired later versus earlier in speech development.

METHOD

Thirty (Experiment 1) and 20 (Experiment 2) college students completed tasks that investigated whether an experimental phoneme-level variable (consonant age of acquisition) similarly affects NWR and lexical-access tasks designed to vary in articulatory, auditory-perceptual, and phonological short-term-memory demands. The lexical-access tasks were performed in silence or with concurrent articulation to explore whether consonant age-of-acquisition effects arise before or after articulatory planning.

RESULTS

NWR accuracy decreased on items comprising later- versus earlier-acquired phonemes. Similar consonant age-of-acquisition effects were observed in accuracy measures of nonword reading and lexical decision performed in silence or with concurrent articulation.

CONCLUSION

Results indicate that NWR performance is sensitive to phoneme-level phonological knowledge in long-term memory. NWR, accordingly, should not be regarded as a diagnostic tool for pure impairment of phonological short-term memory.

SUPPLEMENTAL MATERIALS

https://doi.org/10.23641/asha.5435137.

Common Brain Structure Findings Across Children with Varied Reading Disability Profiles

Dyslexia is a developmental disorder in reading that exhibits varied patterns of expression across children. Here we examined the degree to which different kinds of reading disabilities (defined as profiles or patterns of reading problems) contribute to brain morphology results in Jacobian determinant images that represent local brain shape and volume. A matched-pair brain morphometry approach was used to control for confounding from brain size and research site effects in this retrospective multi-site study of 134 children from eight different research sites. Parietal operculum, corona radiata, and internal capsule differences between cases and controls were consistently observed across children with evidence of classic dyslexia, specific comprehension deficit, and language learning disability. Thus, there can be common brain morphology findings across children with quite varied reading disability profiles that we hypothesize compound the developmental difficulties of children with unique reading disability profiles and reasons for their reading disability.

Word and object recognition during reading acquisition: MEG evidence

Studies on adults suggest that reading-induced brain changes might not be limited to linguistic processes. It is still unclear whether these results can be generalized to reading development. The present study shows to which extent neural responses to verbal and nonverbal stimuli are reorganized while children learn to read. MEG data of thirty Basque children (4-8y) were collected while they were presented with written words, spoken words and visual objects. The evoked fields elicited by the experimental stimuli were compared to their scrambled counterparts. Visual words elicited left posterior (200-300ms) and temporal activations (400-800ms). The size of these effects increased as reading performance improved, suggesting a reorganization of children's visual word responses. Spoken words elicited greater left temporal responses relative to scrambles (300-700ms). No evidence for the influence of reading expertise was observed. Brain responses to objects were greater than to scrambles in bilateral posterior regions (200-500ms). There was a greater left hemisphere involvement as reading errors decreased, suggesting a strengthened verbal decoding of visual configurations with reading acquisition. The present results reveal that learning to read not only influences written word processing, but also affects visual object recognition, suggesting a non-language specific impact of reading on children's neural mechanisms.

Orthographic Activation in L2 Spoken Word Recognition Depends on Proficiency: Evidence from Eye-Tracking

The use of orthographic and phonological information in spoken word recognition was studied in a visual world task where L1 Finnish learners of L2 French (n = 64) and L1 French native speakers (n = 24) were asked to match spoken word forms with printed words while their eye movements were recorded. In Experiment 1, French target words were contrasted with competitors having a longer ( vs. ) or a shorter word initial phonological overlap ( vs. ) and an identical orthographic overlap. In Experiment 2, target words were contrasted with competitors of either longer ( vs. ) or shorter word initial orthographic overlap ( vs. ) and of an identical phonological overlap. A general phonological effect was observed in the L2 listener group but not in the L1 control group. No general orthographic effects were observed in the L2 or L1 groups, but a significant effect of proficiency was observed for orthographic overlap over time: higher proficiency L2 listeners used also orthographic information in the matching task in a time-window from 400 to 700 ms, whereas no such effect was observed for lower proficiency listeners. These results suggest that the activation of orthographic information in L2 spoken word recognition depends on proficiency in L2.

Effects of orthographic consistency and homophone density on Chinese spoken word recognition

Studies of alphabetic language have shown that orthographic knowledge influences phonological processing during spoken word recognition. This study utilized the Event-Related Potentials (ERPs) to differentiate two types of phonology-to-orthography (P-to-O) mapping consistencies in Chinese, namely homophone density and orthographic consistency. The ERP data revealed an orthographic consistency effect in the frontal-centrally distributed N400, and a homophone density effect in central-posteriorly distributed late positive component (LPC). Further source analyses using the standardized low-resolution electromagnetic tomography (sLORETA) demonstrated that the orthographic effect was not only localized in the frontal and temporal-parietal regions for phonological processing, but also in the posterior visual cortex for orthographic processing, while the homophone density effect was found in middle temporal gyrus for lexical-semantic selection, and in the temporal-occipital junction for orthographic processing. These results suggest that orthographic information not only shapes the nature of phonological representations, but may also be activated during on-line spoken word recognition.

Neural Correlates of Morphological Processing: Evidence from Chinese

Morphological decomposition is an important part of complex word processing. In Chinese, this requires a comprehensive consideration of phonological, orthographic and morphemic information. The left inferior frontal gyrus (L-IFG) has been implicated in this process in alphabetic languages. However, it is unclear whether the neural mechanisms underlying morphological processing in alphabetic languages would be the same in Chinese, a logographic language. To investigate the neural basis of morphological processing in Chinese compound words, an fMRI experiment was conducted using an explicit auditory morphological judgment task. Results showed the L-IFG to be a core area in Chinese morphological processing, consistent with research in alphabetic languages. Additionally, a broad network consisting of the L-MTG, the bilateral STG and the L-FG that taps phonological, orthographic, and semantic information was found to be involved. These results provide evidence that the L-IFG plays an important role in morphological processing even in languages that are typologically different.

The neurophysiology of language: Insights from non-invasive brain stimulation in the healthy human brain

With the advent of non-invasive brain stimulation (NIBS), a new decade in the study of language has started. NIBS allows for testing the functional relevance of language-related brain activation and enables the researcher to investigate how neural activation changes in response to focal perturbations. This review focuses on the application of NIBS in the healthy brain. First, some basic mechanisms will be introduced and the prerequisites for carrying out NIBS studies of language are addressed. The next section outlines how NIBS can be used to characterize the contribution of the stimulated area to a task. In this context, novel approaches such as multifocal transcranial magnetic stimulation and the condition-and-perturb approach are discussed. The third part addresses the combination of NIBS and neuroimaging in the study of plasticity. These approaches are particularly suited to investigate short-term reorganization in the healthy brain and may inform models of language recovery in post-stroke aphasia.

Hemispheric specialization for visual words is shaped by attention to sublexical units during initial learning

Selective attention to grapheme-phoneme mappings during learning can impact the circuitry subsequently recruited during reading. Here we trained literate adults to read two novel scripts of glyph words containing embedded letters under different instructions. For one script, learners linked each embedded letter to its corresponding sound within the word (grapheme-phoneme focus); for the other, decoding was prevented so entire words had to be memorized. Post-training, ERPs were recorded during a reading task on the trained words within each condition and on untrained but decodable (transfer) words. Within this condition, reaction-time patterns suggested both trained and transfer words were accessed via sublexical units, yet a left-lateralized, late ERP response showed an enhanced left lateralization for transfer words relative to trained words, potentially reflecting effortful decoding. Collectively, these findings show that selective attention to grapheme-phoneme mappings during learning drives the lateralization of circuitry that supports later word recognition. This study thus provides a model example of how different instructional approaches to the same material may impact changes in brain circuitry.

Delayed Anticipatory Spoken Language Processing in Adults with Dyslexia—Evidence from Eye-tracking

It is now well established that anticipation of upcoming input is a key characteristic of spoken language comprehension. It has also frequently been observed that literacy influences spoken language processing. Here, we investigated whether anticipatory spoken language processing is related to individuals' word reading abilities. Dutch adults with dyslexia and a control group participated in two eye-tracking experiments. Experiment 1 was conducted to assess whether adults with dyslexia show the typical language-mediated eye gaze patterns. Eye movements of both adults with and without dyslexia closely replicated earlier research: spoken language is used to direct attention to relevant objects in the environment in a closely time-locked manner. In Experiment 2, participants received instructions (e.g., 'Kijk naar de(COM) afgebeelde piano(COM)', look at the displayed piano) while viewing four objects. Articles (Dutch 'het' or 'de') were gender marked such that the article agreed in gender only with the target, and thus, participants could use gender information from the article to predict the target object. The adults with dyslexia anticipated the target objects but much later than the controls. Moreover, participants' word reading scores correlated positively with their anticipatory eye movements. We conclude by discussing the mechanisms by which reading abilities may influence predictive language processing.

How Early Does the Brain Distinguish between Regular Words, Irregular Words, and Pseudowords during the Reading Process? Evidence from Neurochronometric TMS

Cognitive theories on reading propose that the characteristics of written stimuli determine how they are processed in the brain. However, whether the brain distinguishes between regular words, irregular words, and pseudowords already at an early stage of the reading process is still subject to debate. Here we used chronometric TMS to address this issue. During the first 140 msec of regular word, irregular word, and pseudoword reading, TMS was used to disrupt the function of the ventral occipitotemporal, posterior middle temporal, and supramarginal gyri, which are key areas involved in orthographic, semantic, and phonological processing, respectively. Early TMS stimulation delivered on posterior middle temporal and supramarginal gyri affected regular and irregular word, but not pseudoword, reading. In contrast, ventral occipitotemporal disruption affected both word and pseudoword reading. We thus found evidence for an early distinction between word and pseudoword processing in the semantic and phonological systems, but not in the orthographic system.

Neural mechanisms underlying the computation of hierarchical tree structures in mathematics

Whether mathematical and linguistic processes share the same neural mechanisms has been a matter of controversy. By examining various sentence structures, we recently demonstrated that activations in the left inferior frontal gyrus (L. IFG) and left supramarginal gyrus (L. SMG) were modulated by the Degree of Merger (DoM), a measure for the complexity of tree structures. In the present study, we hypothesize that the DoM is also critical in mathematical calculations, and clarify whether the DoM in the hierarchical tree structures modulates activations in these regions. We tested an arithmetic task that involved linear and quadratic sequences with recursive computation. Using functional magnetic resonance imaging, we found significant activation in the L. IFG, L. SMG, bilateral intraparietal sulcus (IPS), and precuneus selectively among the tested conditions. We also confirmed that activations in the L. IFG and L. SMG were free from memory-related factors, and that activations in the bilateral IPS and precuneus were independent from other possible factors. Moreover, by fitting parametric models of eight factors, we found that the model of DoM in the hierarchical tree structures was the best to explain the modulation of activations in these five regions. Using dynamic causal modeling, we showed that the model with a modulatory effect for the connection from the L. IPS to the L. IFG, and with driving inputs into the L. IFG, was highly probable. The intrinsic, i.e., task-independent, connection from the L. IFG to the L. IPS, as well as that from the L. IPS to the R. IPS, would provide a feedforward signal, together with negative feedback connections. We indicate that mathematics and language share the network of the L. IFG and L. IPS/SMG for the computation of hierarchical tree structures, and that mathematics recruits the additional network of the L. IPS and R. IPS.

Inferior parietal lobule contributions to visual word recognition

This study investigated how the left inferior parietal lobule (IPL) contributes to visual word recognition. We used repetitive TMS to temporarily disrupt neural information processing in two anatomical fields of the IPL, namely, the angular (ANG) and supramarginal (SMG) gyri, and observed the effects on reading tasks that focused attention on either the meaning or sounds of written words. Relative to no TMS, stimulation of the left ANG selectively slowed responses in the meaning, but not sound, task, whereas stimulation of the left SMG affected responses in the sound, but not meaning, task. These results demonstrate that ANG and SMG doubly dissociate in their contributions to visual word recognition. We suggest that this functional division of labor may be understood in terms of the distinct patterns of cortico-cortical connectivity resulting in separable functional circuits.

Transcranial magnetic stimulation for investigating causal brain-behavioral relationships and their time course

Transcranial magnetic stimulation (TMS) is a safe, non-invasive brain stimulation technique that uses a strong electromagnet in order to temporarily disrupt information processing in a brain region, generating a short-lived "virtual lesion." Stimulation that interferes with task performance indicates that the affected brain region is necessary to perform the task normally. In other words, unlike neuroimaging methods such as functional magnetic resonance imaging (fMRI) that indicate correlations between brain and behavior, TMS can be used to demonstrate causal brain-behavior relations. Furthermore, by varying the duration and onset of the virtual lesion, TMS can also reveal the time course of normal processing. As a result, TMS has become an important tool in cognitive neuroscience. Advantages of the technique over lesion-deficit studies include better spatial-temporal precision of the disruption effect, the ability to use participants as their own control subjects, and the accessibility of participants. Limitations include concurrent auditory and somatosensory stimulation that may influence task performance, limited access to structures more than a few centimeters from the surface of the scalp, and the relatively large space of free parameters that need to be optimized in order for the experiment to work. Experimental designs that give careful consideration to appropriate control conditions help to address these concerns. This article illustrates these issues with TMS results that investigate the spatial and temporal contributions of the left supramarginal gyrus (SMG) to reading.

How does reading performance modulate the impact of orthographic knowledge on speech processing? A comparison of normal readers and dyslexic adults

Studies on proficient readers showed that speech processing is affected by knowledge of the orthographic code. Yet, the automaticity of the orthographic influence depends on task demand. Here, we addressed this automaticity issue in normal and dyslexic adult readers by comparing the orthographic effects obtained in two speech processing tasks that are or not sensitive to strategies developed by participants. Our finding showed that while participants' performance in a metaphonological task, which is known to be strategy prone, was affected by their orthographic knowledge regardless of the childhood diagnosis of dyslexia or of their actual reading-related skills, this latter factor significantly modulated the orthographic influence found in a more natural speech recognition task. The finding supports the claim that while any individuals who know a reading code are able to resort to their orthographic knowledge when they process speech, a more profound modification of the speech processing system by the orthographic code takes place only in readers who have reached a certain level of reading expertise.

The Association between Gray Matter Volume and Reading Proficiency: A Longitudinal Study of Beginning Readers

Neural systems involved in the processing of written language have been identified by a number of functional imaging studies. Structural changes in cortical anatomy that occur in the course of literacy acquisition, however, remain largely unknown. Here, we follow elementary school children over their first 2 years of formal reading instruction and use tensor-based morphometry to relate reading proficiency to cortical volume at baseline and follow-up measurement as well as to intraindividual longitudinal volume development between the two measurement time points. A positive relationship was found between baseline gray matter volume in the left superior temporal gyrus and subsequent changes in reading proficiency. Furthermore, a negative relationship was found between reading proficiency at the second measurement time point and intraindividual cortical volume development in the inferior parietal lobule and the precentral and postcentral gyri of the left hemisphere. These results are interpreted as evidence that reading acquisition is associated with preexisting structural differences as well as with experience-dependent structural changes involving dendritic and synaptic pruning.

Computational principles of syntax in the regions specialized for language: integrating theoretical linguistics and functional neuroimaging

The nature of computational principles of syntax remains to be elucidated. One promising approach to this problem would be to construct formal and abstract linguistic models that parametrically predict the activation modulations in the regions specialized for linguistic processes. In this article, we review recent advances in theoretical linguistics and functional neuroimaging in the following respects. First, we introduce the two fundamental linguistic operations: Merge (which combines two words or phrases to form a larger structure) and Search (which searches and establishes a syntactic relation of two words or phrases). We also illustrate certain universal properties of human language, and present hypotheses regarding how sentence structures are processed in the brain. Hypothesis I is that the Degree of Merger (DoM), i.e., the maximum depth of merged subtrees within a given domain, is a key computational concept to properly measure the complexity of tree structures. Hypothesis II is that the basic frame of the syntactic structure of a given linguistic expression is determined essentially by functional elements, which trigger Merge and Search. We then present our recent functional magnetic resonance imaging experiment, demonstrating that the DoM is indeed a key syntactic factor that accounts for syntax-selective activations in the left inferior frontal gyrus and supramarginal gyrus. Hypothesis III is that the DoM domain changes dynamically in accordance with iterative Merge applications, the Search distances, and/or task requirements. We confirm that the DoM accounts for activations in various sentence types. Hypothesis III successfully explains activation differences between object- and subject-relative clauses, as well as activations during explicit syntactic judgment tasks. A future research on the computational principles of syntax will further deepen our understanding of uniquely human mental faculties.

Reading impairment in an adolescent with temporo-occipital epilepsy. Pre- and post-surgical evaluation

We present a 16 year-old right-handed case who underwent a left temporo-occipital resection to treat intractable epilepsy. Pre- and post-surgical evaluations showed an average intellectual quotient, preserved abilities in language and visuo-spatial functions and increased reading and spelling deficits (difficulties with irregular words, homophones and phonologically valid spelling errors of irregularly spelled words, associated with preserved performances in non-words). This pattern of characteristic lexical route deficits highlights the major role of the temporo-occipital areas in reading acquisition. We discussed the consequences of temporo-occipital dysfunction on reading.

Effects of rhyme and spelling patterns on auditory word ERPs depend on selective attention to phonology

ERP responses to spoken words are sensitive to both rhyming effects and effects of associated spelling patterns. Are such effects automatically elicited by spoken words or dependent on selectively attending to phonology? To address this question, ERP responses to spoken word pairs were investigated under two equally demanding listening tasks that directed selective attention either to sub-syllabic phonology (i.e., rhyme judgments) or to melodies embedded within the words. ERPs elicited when participants selectively attended to phonology demonstrated a rhyming effect that was concurrent with online stimulus encoding and an orthographic effect that emerged later. ERP responses to the same stimuli presented under melodic focus, however, showed no evidence of sensitivity to rhyme or spelling patterns. Results reveal limitations to the automaticity of such ERP effects, suggesting that rhyme effects may depend, at least to some degree, on allocation of attention to phonology, which may in turn activate task-incidental orthographic information.

Syntactic computation in the human brain: the degree of merger as a key factor

Our goal of this study is to characterize the functions of language areas in most precise terms. Previous neuroimaging studies have reported that more complex sentences elicit larger activations in the left inferior frontal gyrus (L. F3op/F3t), although the most critical factor still remains to be identified. We hypothesize that pseudowords with grammatical particles and morphosyntactic information alone impose a construction of syntactic structures, just like normal sentences, and that "the Degree of Merger" (DoM) in recursively merged sentences parametrically modulates neural activations. Using jabberwocky sentences with distinct constructions, we fitted various parametric models of syntactic, other linguistic, and nonlinguistic factors to activations measured with functional magnetic resonance imaging. We demonstrated that the models of DoM and "DoM+number of Search (searching syntactic features)" were the best to explain activations in the L. F3op/F3t and supramarginal gyrus (L. SMG), respectively. We further introduced letter strings, which had neither lexical associations nor grammatical particles, but retained both matching orders and symbol orders of sentences. By directly contrasting jabberwocky sentences with letter strings, localized activations in L. F3op/F3t and L. SMG were indeed independent of matching orders and symbol orders. Moreover, by using dynamic causal modeling, we found that the model with a inhibitory modulatory effect for the bottom-up connectivity from L. SMG to L. F3op/F3t was the best one. For this best model, the top-down connection from L. F3op/F3t to L. SMG was significantly positive. By using diffusion-tensor imaging, we confirmed that the left dorsal pathway of the superior longitudinal and arcuate fasciculi consistently connected these regions. Lastly, we established that nonlinguistic order-related and error-related factors significantly activated the right (R.) lateral premotor cortex and R. F3op/F3t, respectively. These results indicate that the identified network of L. F3op/F3t and L. SMG subserves the calculation of DoM in recursively merged sentences.

The Science of Reading and Its Educational Implications

Research in cognitive science and neuroscience has made enormous progress toward understanding skilled reading, the acquisition of reading skill, the brain bases of reading, the causes of developmental reading impairments and how such impairments can be treated. My question is: if the science is so good, why do so many people read so poorly? I mainly focus on the United States, which fares poorly on cross-national comparisons of literacy, with about 25-30% of the population exhibiting literacy skills that are low by standard metrics. I consider three possible contributing factors, all of which turn on issues concerning the relationships between written and spoken language. They are: the fact that English has a deep alphabetic orthography; how reading is taught; and the impact of linguistic variability as manifested in the Black-White "achievement gap". I conclude that there are opportunities to increase literacy levels by making better use of what we have learned about reading and language, but also institutional obstacles and understudied issues for which more evidence is badly needed.

Language

Noninvasive focal brain stimulation by means of transcranial magnetic stimulation (TMS) has been used extensively in the past 20 years to investigate normal language functions. The picture emerging from this collection of empirical works is that of several independent modular functions mapped on left-lateralized temporofrontal circuits originating dorsally or ventrally to the auditory cortex. The identification of sounds as language (i.e., phonological transformations) is modulated by TMS applied over the posterior-superior temporal cortex and over the caudal inferior frontal gyrus/ventral premotor cortex complex. Conversely, attribution of semantics to words is modulated successfully by applying TMS to the rostral part of the inferior frontal gyrus. Speech production is typically interfered with by TMS applied to the left inferior frontal gyrus, onto the same cortical areas that also contain phonological representations. The cortical mapping of grammatical functions has been investigated with TMS mainly regarding the category of verbs, which seem to be represented in the left middle frontal gyrus. Most TMS studies have investigated the cortical processing of single words or sublexical elements. Conversely, complex elements of language such as syntax have not been investigated extensively, although a few studies have indicated a left temporal, frontal, and parietal system also involving the neocerebellar cortex. Finally, both the perception and production of nonlinguistic communicative properties of speech, such as prosody, have been mapped by TMS in the peri-Silvian region of the right hemisphere.

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.

Early and sustained supramarginal gyrus contributions to phonological processing

Reading is a difficult task that, at a minimum, requires recognizing a visual stimulus and linking it with its corresponding sound and meaning. Neurologically, this involves an anatomically distributed set of brain regions cooperating to solve the problem. It has been hypothesized that the supramarginal gyrus (SMG) contributes preferentially to phonological aspects of word processing and thus plays an important role in visual word recognition. Here, we used chronometric transcranial magnetic stimulation (TMS) to investigate the functional specificity and timing of SMG involvement in reading visually presented words. Participants performed tasks designed to focus on either the phonological, semantic, or visual aspects of written words while double pulses of TMS (delivered 40 ms apart) were used to temporarily interfere with neural information processing in the left SMG at five different time windows. Stimulation at 80/120, 120/160, and 160/200 ms post-stimulus onset significantly slowed subjects' reaction times in the phonological task. This inhibitory effect was specific to the phonological condition, with no effect of TMS in the semantic or visual tasks, consistent with claims that SMG contributes preferentially to phonological aspects of word processing. The fact that the effect began within 80-120 ms of the onset of the stimulus and continued for approximately 100 ms, indicates that phonological processing initiates early and is sustained over time. These findings are consistent with accounts of visual word recognition that posit parallel activation of orthographic, phonological, and semantic information that interact over time to settle into a distributed, but stable, representation of a word.

Orthographic Contamination of Broca's Area

Strong evidence has accumulated over the past years suggesting that orthography plays a role in spoken language processing. It is still unclear, however, whether the influence of orthography on spoken language results from a co-activation of posterior brain areas dedicated to low-level orthographic processing or whether it results from orthographic restructuring of phonological representations located in the anterior perisylvian speech network itself. To test these hypotheses, we ran a fMRI study that tapped orthographic processing in the visual and auditory modalities. As a marker for orthographic processing, we used the orthographic decision task in the visual modality and the orthographic consistency effect in the auditory modality. Results showed no specific orthographic activation neither for the visual nor the auditory modality in left posterior occipito-temporal brain areas that are thought to host the visual word form system. In contrast, specific orthographic activation was found both for the visual and auditory modalities at anterior sites belonging to the perisylvian region: the left dorsal-anterior insula and the left inferior frontal gyrus. These results are in favor of the restructuring hypothesis according to which learning to read acts like a "virus" that permanently contaminates the spoken language system.

Naming in noise: the contribution of orthographic knowledge to speech repetition

While the influence of orthographic knowledge on lexical and postlexical speech processing tasks has been consistently observed, it is not the case in tasks that can be performed at the prelexical level. The present study re-examined the orthographic consistency effect in such a task, namely in shadowing. Comparing the situation where the acoustic signal was clearly presented to the situation where it was embedded in noise, we observed that the orthographic effect was restricted to the latter situation and only to high-frequency words. This finding supports the lexical account of the orthographic effects in speech recognition tasks and illustrates the ability of the cognitive system to adjust itself as a function of task difficulty by resorting to the appropriate processing mechanism and information in order to maintain a good level of performance.

Naming in noise: the contribution of orthographic knowledge to speech repetition

While the influence of orthographic knowledge on lexical and postlexical speech processing tasks has been consistently observed, it is not the case in tasks that can be performed at the prelexical level. The present study re-examined the orthographic consistency effect in such a task, namely in shadowing. Comparing the situation where the acoustic signal was clearly presented to the situation where it was embedded in noise, we observed that the orthographic effect was restricted to the latter situation and only to high-frequency words. This finding supports the lexical account of the orthographic effects in speech recognition tasks and illustrates the ability of the cognitive system to adjust itself as a function of task difficulty by resorting to the appropriate processing mechanism and information in order to maintain a good level of performance.

Literacy Affects Spoken Language in a Non-Linguistic Task: An ERP Study

It is now commonly accepted that orthographic information influences spoken word recognition in a variety of laboratory tasks (lexical decision, semantic categorization, gender decision). However, it remains a hotly debated issue whether or not orthography would influence normal word perception in passive listening. That is, the argument has been made that orthography might only be activated in laboratory tasks that require lexical or semantic access in some form or another. It is possible that these rather "unnatural" tasks invite participants to use orthographic information in a strategic way to improve task performance. To put the strategy account to rest, we conducted an event-related brain potential (ERP) study, in which participants were asked to detect a 500-ms-long noise burst that appeared on 25% of the trials (Go trials). In the NoGo trials, we presented spoken words that were orthographically consistent or inconsistent. Thus, lexical and/or semantic processing was not required in this task and there was no strategic benefit in computing orthography to perform this task. Nevertheless, despite the non-linguistic nature of the task, we replicated the consistency effect that has been previously reported in lexical decision and semantic tasks (i.e., inconsistent words produce more negative ERPs than consistent words as early as 300 ms after the onset of the spoken word). These results clearly suggest that orthography automatically influences word perception in normal listening even if there is no strategic benefit to do so. The results are explained in terms of orthographic restructuring of phonological representations.

Orthographic consistency and word-frequency effects in auditory word recognition: new evidence from lexical decision and rime detection

Many studies have repeatedly shown an orthographic consistency effect in the auditory lexical decision task. Words with phonological rimes that could be spelled in multiple ways (i.e., inconsistent words) typically produce longer auditory lexical decision latencies and more errors than do words with rimes that could be spelled in only one way (i.e., consistent words). These results have been extended to different languages and tasks, suggesting that the effect is quite general and robust. Despite this growing body of evidence, some psycholinguists believe that orthographic effects on spoken language are exclusively strategic, post-lexical, or restricted to peculiar (low-frequency) words. In the present study, we manipulated consistency and word-frequency orthogonally in order to explore whether the orthographic consistency effect extends to high-frequency words. Two different tasks were used: lexical decision and rime detection. Both tasks produced reliable consistency effects for both low- and high-frequency words. Furthermore, in Experiment 1 (lexical decision), an interaction revealed a stronger consistency effect for low-frequency words than for high-frequency words, as initially predicted by Ziegler and Ferrand (1998), whereas no interaction was found in Experiment 2 (rime detection). Our results extend previous findings by showing that the orthographic consistency effect is obtained not only for low-frequency words but also for high-frequency words. Furthermore, these effects were also obtained in a rime detection task, which does not require the explicit processing of orthographic structure. Globally, our results suggest that literacy changes the way people process spoken words, even for frequent words.