Poor neural and perceptual phoneme discrimination during acoustic variation in dyslexia

Unraveling Brain Synchronisation Dynamics by Explainable Neural Networks using EEG Signals: Application to Dyslexia Diagnosis

The electrical activity of the neural processes involved in cognitive functions is captured in EEG signals, allowing the exploration of the integration and coordination of neuronal oscillations across multiple spatiotemporal scales. We have proposed a novel approach that combines the transformation of EEG signal into image sequences, considering cross-frequency phase synchronisation (CFS) dynamics involved in low-level auditory processing, with the development of a two-stage deep learning model for the detection of developmental dyslexia (DD). This deep learning model exploits spatial and temporal information preserved in the image sequences to find discriminative patterns of phase synchronisation over time achieving a balanced accuracy of up to 83%. This result supports the existence of differential brain synchronisation dynamics between typical and dyslexic seven-year-old readers. Furthermore, we have obtained interpretable representations using a novel feature mask to link the most relevant regions during classification with the cognitive processes attributed to normal reading and those corresponding to compensatory mechanisms found in dyslexia.

Tracking reading skills and reading-related skills in dyslexia before (age 5) and after (ages 10-17) diagnosis

This study had three goals: to examine the stability of deficits in the phonological and lexical routes in dyslexia (group study), to determine the prevalence of dyslexia profiles (multiple-case study), and to identify the prediction of phonemic segmentation and discrimination skills before reading acquisition on future reading level. Among a group of 373 non-readers seen at age 5, 38 students were subsequently diagnosed as either consistent dyslexic readers (18 DYS) or consistent typical readers (20 TR). Their phonological and lexical reading skills were assessed at ages 10 and 17 and their phonemic segmentation and discrimination skills at age 5. In comparison with TR of the same chronological age (CA-TR), individuals with dyslexia demonstrated an impairment of the two reading routes, especially of the phonological reading route. In the comparison with younger TR (age 10) of the same reading level (RL-TR), only a deficit of the phonological route is observed. In the multiple-case study, the comparisons with CA-TR showed a prevalence of mixed profiles and very few dissociated profiles, whereas the comparison with RL-TR resulted mostly in two profiles depending on the measure: a phonological profile when accuracy was used and a delayed profile when speed was used. In addition, the correlations between early phonemic segmentation and discrimination skills (age 5) and later reading skills (age 17) were significant, and in the group of individuals with dyslexia, early phonemic segmentation skills significantly predicted these later reading skills. Phonological reading deficits are persistent and mainly caused by early phonemic impairments.

Auditory Discrimination-A Missing Piece of Speech and Language Development: A Study on 6-9-Year-Old Children with Auditory Processing Disorder

Auditory discrimination, the hearing ability crucial for speech and language development, allowing one to perceive changes in volume, duration and frequency of sounds, was assessed for 366 participants with normal peripheral hearing: 220 participants with auditory processing disorders (APD) and 146 typically developing (TD) children, all aged 6-9 years. Discrimination of speech was tested with nonsense words using the phoneme discrimination test (PDT), while pure tones-with the frequency pattern test (FPT). The obtained results were statistically analyzed and correlated. The median of the FPT results obtained by participants with APD was more than twice lower than those of TD (20% vs. 50%; p < 0.05), similarly in the PDT (21 vs. 24; p < 0.05). The FPT results of 9-year-old APD participants were worse than the results of TD 6-year-olds (30% vs. 40%; p < 0.05), indicating that the significant FPT deficit strongly suggests APD. The process of auditory discrimination development does not complete with the acquisition of phonemes but continues during school age. Physiological phonemes discrimination is not yet equalized among 9-year-olds. Nonsense word tests allow for reliable testing of phoneme discrimination. APD children require testing with PDT and FPT because both test results allow for developing individual therapeutic programs.

Modulation of auditory temporal processing, speech in noise perception, auditory-verbal memory, and reading efficiency by anodal tDCS in children with dyslexia

Dyslexia is a neurodevelopmental disorder that is prevalent in children. It is estimated that 30-50% of individuals diagnosed with dyslexia also manifest an auditory perceptual deficit characteristic of auditory processing disorder (APD). Some studies suggest that defects in basic auditory processing can lead to phonological defects as the most prominent cause of dyslexia. Thus, in some cases, there may be interrelationships between dyslexia and some of the aspects of central auditory processing. In recent years, transcranial direct current stimulation (tDCS) has been used as a safe method for the modulation of central auditory processing aspects in healthy adults and reading skills in children with dyslexia. Therefore, the objectives of our study were to investigate the effect of tDCS on the modulation of different aspects of central auditory processing, aspects of reading, and the relationship between these two domains in dyslexic children with APD. A within-subjects design was employed to investigate the effect of two electrode arrays (the anode on the left STG (AC)/cathode on the right shoulder and anode on the left STG/cathode on the right STG) on auditory temporal processing; speech-in-noise perception, short-term auditory memory; and high-frequency word, low-frequency word, pseudoword, and text reading. The results of this clinical trial showed the modulation of the studied variables in central auditory processing and the accuracy and speed of reading variables compared to the control and sham statuses in both electrode arrays. Our results also showed that the improvement of the accuracy and speed of text reading, as well as the accuracy of pseudoword reading were related to the improvement of speech in noise perception and temporal processing. The results of this research can be effective in clarifying the basis of the neurobiology of dyslexia and, in particular, the hypothesis of the role of basic auditory processing and subsequently the role of the auditory cortex in dyslexia. These results might provide a framework to facilitate behavioral rehabilitation in dyslexic children with APD.

Phoneme Categorization in Prelingually Deaf Adult Cochlear Implant Users

PURPOSE

Phoneme categorization (PC) for voice onset time and second formant transition was studied in adult cochlear implant (CI) users with early-onset deafness and hearing controls.

METHOD

Identification and discrimination tasks were administered to 30 participants implanted before 4 years of age, 21 participants implanted after 7 years of age, and 21 hearing individuals.

RESULTS

Distinctive identification and discrimination functions confirmed PC within all groups. Compared to hearing participants, the CI groups generally displayed longer/higher category boundaries, shallower identification function slopes, reduced identification consistency, and reduced discrimination performance. A principal component analysis revealed that identification consistency, discrimination accuracy, and identification function slope, but not boundary location, loaded on a single factor, reflecting general PC performance. Earlier implantation was associated with better PC performance within the early CI group, but not the late CI group. Within the early CI group, earlier implantation age but not PC performance was associated with better speech recognition. Conversely, within the late CI group, better PC performance but not earlier implantation age was associated with better speech recognition.

CONCLUSIONS

Results suggest that implantation timing within the sensitive period before 4 years of age partly determines the level of PC performance. They also suggest that early implantation may promote development of higher level processes that can compensate for relatively poor PC performance, as can occur in challenging listening conditions.

Later but Not Weaker: Neural Categorization of Native Vowels of Children at Familial Risk of Dyslexia

Although allophonic speech processing has been hypothesized to be a contributing factor in developmental dyslexia, experimental evidence is limited and inconsistent. The current study compared the categorization of native similar sounding vowels of typically developing (TD) children and children at familial risk (FR) of dyslexia. EEG response was collected in a non-attentive passive oddball paradigm from 35 TD and 35 FR Dutch 20-month-old infants who were matched on vocabulary. The children were presented with two nonwords “giep” [ɣip] and “gip” [ɣIp] that contrasted solely with respect to the vowel. In the multiple-speaker condition, both nonwords were produced by twelve different speakers while in the single-speaker condition, single tokens of each word were used as stimuli. For both conditions and for both groups, infant positive mismatch response (p-MMR) was elicited, and the p-MMR amplitude was comparable between the two groups, although the FR children had a later p-MMR peak than the TD children in the multiple-speaker condition. These findings indicate that FR children are able to categorize speech sounds, but that they may do so in a more effortful way than TDs.

Reduced Learning of Sound Categories in Dyslexia Is Associated with Reduced Regularity-Induced Auditory Cortex Adaptation

A main characteristic of dyslexia is poor use of sound categories. We now studied within-session learning of new sound categories in dyslexia, behaviorally and neurally, using fMRI. Human participants (males and females) with and without dyslexia were asked to discriminate which of two serially-presented tones had a higher pitch. The task was administered in two protocols, with and without a repeated reference frequency. The reference condition introduces regularity, and enhances frequency sensitivity in typically developing (TD) individuals. Enhanced sensitivity facilitates the formation of "high" and "low" pitch categories above and below this reference, respectively. We found that in TDs, learning was paralleled by a gradual decrease in activation of the primary auditory cortex (PAC), and reduced activation of the superior temporal gyrus (STG) and left posterior parietal cortex (PPC), which are important for using sensory history. No such sensitivity was found among individuals with dyslexia (IDDs). Rather, IDDs showed reduced behavioral learning of stimulus regularities and no regularity-associated adaptation in the auditory cortex or in higher-level regions. We propose that IDDs' reduced cortical adaptation, associated with reduced behavioral learning of sound regularities, underlies their impoverished use of stimulus history, and consequently impedes their formation of rich sound categories.SIGNIFICANCE STATEMENT Reading difficulties in dyslexia are often attributed to poor use of phonological categories. To test whether poor category use could result from poor learning of new sound categories in general, we administered an auditory discrimination task that examined the learning of new pitch categories above and below a repeated reference sound. Individuals with dyslexia (IDDs) learned categories slower than typically developing (TD) individuals. TD individuals showed adaptation to the repeated sounds that paralleled the category learning in their primary auditory cortex (PAC) and other higher-level regions. In dyslexia, no brain region showed such adaptation. We suggest that poor learning of sound statistics in sensory regions may underlie the poor representations of both speech and nonspeech categories in dyslexia.

How Learning to Read Changes the Listening Brain

Reading acquisition reorganizes existing brain networks for speech and visual processing to form novel audio-visual language representations. This requires substantial cortical plasticity that is reflected in changes in brain activation and functional as well as structural connectivity between brain areas. The extent to which a child's brain can accommodate these changes may underlie the high variability in reading outcome in both typical and dyslexic readers. In this review, we focus on reading-induced functional changes of the dorsal speech network in particular and discuss how its reciprocal interactions with the ventral reading network contributes to reading outcome. We discuss how the dynamic and intertwined development of both reading networks may be best captured by approaching reading from a skill learning perspective, using audio-visual learning paradigms and longitudinal designs to follow neuro-behavioral changes while children's reading skills unfold.

Impaired Perception and Neural Processing of Rules in Developmental Dyslexia

Rules and regularities of language are typically processed in an implicit and effortless way in the human brain. Individuals with developmental dyslexia have problems in implicit learning of regularities in sequential stimuli, but the neural basis of this deficit has not been studied. This study investigated extraction and utilization of a complex auditory rule at neural and perceptual levels in 18 adults with dyslexia and 20 typical readers. Mismatch negativity (MMN) and P3a responses to rule violations in speech stimuli, reflecting change detection and attention switch, respectively, were recorded with electroencephalogram. Both groups reported no or little explicit awareness of the rule, suggesting implicit processing. People with dyslexia showed deficient extraction of the rule evidenced by diminished MMNs estimated to originate particularly from the left perisylvian region. The group difference persisted in the attentive condition after the participants were told about the rule, and behavioral detection of the rule violations was poor in people with dyslexia, possibly suggesting difficulties also in utilizing explicit information of the rule. Based on these results, the speech processing difficulties in dyslexia extend beyond phoneme discrimination and basic auditory feature extraction. Challenges in implicit extraction and effortless adoption of complex auditory rules may be central to language learning difficulties in dyslexia.

Newborns' neural processing of native vowels reveals directional asymmetries

Prenatal learning of speech rhythm and melody is well documented. Much less is known about the earliest acquisition of segmental speech categories. We tested whether newborn infants perceive native vowels, but not nonspeech sounds, through some existing (proto-)categories, and whether they do so more robustly for some vowels than for others. Sensory event-related potentials (ERP), and mismatch responses (MMR), were obtained from 104 neonates acquiring Czech. The ERPs elicited by vowels were larger than the ERPs to nonspeech sounds, and reflected the differences between the individual vowel categories. The MMRs to changes in vowels but not in nonspeech sounds revealed left-lateralized asymmetrical processing patterns: a change from a focal [a] to a nonfocal [ɛ], and the change from short [ɛ] to long [ɛ:] elicited more negative MMR responses than reverse changes. Contrary to predictions, we did not find evidence of a developmental advantage for vowel length contrasts (supposedly most readily available in utero) over vowel quality contrasts (supposedly less salient in utero). An explanation for these asymmetries in terms of differential degree of prior phonetic warping of speech sounds is proposed. Future studies with newborns with different language backgrounds should test whether the prenatal learning scenario proposed here is plausible.

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Newborns’ processing of native vowels and comparable nonspeech sounds differ.

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Durational and spectral differences in stimuli were more clearly reflected by the ERPs to vowels, compared to tone complexes.

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Directional asymmetries were detected in the mismatch responses to vowel deviants.

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In the left hemisphere, a change in vowels from focal to nonfocal and from short to long resulted in a more negative MMR.

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The findings may be explained by phonetic learning prior to the 3rd day after birth.

Detecting Phase-Synchrony Connectivity Anomalies in EEG Signals. Application to Dyslexia Diagnosis

Objective Dyslexia diagnosis is a challenging task, since traditional diagnosis methods are not based on biological markers but on behavioural tests. Although dyslexia diagnosis has been addressed by these tests in clinical practice, it is difficult to extract information about the brain processes involved in the different tasks and, then, to go deeper into its biological basis. Thus, the use of biomarkers can contribute not only to the diagnosis but also to a better understanding of specific learning disorders such as dyslexia. In this work, we use Electroencephalography (EEG) signals to discover differences among controls and dyslexic subjects using signal processing and artificial intelligence techniques. Specifically, we measure phase synchronization among channels, to reveal the functional brain network activated during auditory processing. On the other hand, to explore synchronicity patterns risen by low-level auditory processing, we used specific stimuli consisting in band-limited white noise, modulated in amplitude at different frequencies. The differential information contained in the functional (i.e., synchronization) network has been processed by an anomaly detection system that addresses the problem of subjects variability by an outlier-detection method based on vector quantization. The results, obtained for 7 years-old children, show that the proposed method constitutes an useful tool for clinical use, with the area under ROC curve (AUC) values up to 0.95 in differential diagnosis tasks.

Dysfunctional auditory gamma oscillations in developmental dyslexia: A potential target for a tACS-based intervention

Interventions in developmental dyslexia typically consist of orthography-based reading and writing trainings. However, their efficacy is limited and, consequently, the symptoms persist into adulthood. Critical for this lack of efficacy is the still ongoing debate about the core deficit in dyslexia and its underlying neurobiological causes. There is ample evidence on phonological as well as auditory temporal processing deficits in dyslexia and, on the other hand, cortical gamma oscillations in the auditory cortex as functionally relevant for the extraction of linguistically meaningful information units from the acoustic signal. The present work aims to shed more light on the link between auditory gamma oscillations, phonological awareness, and literacy skills in dyslexia. By mean of EEG, individual gamma frequencies were assessed in a group of children and adolescents diagnosed with dyslexia as well as in an age-matched control group with typical literacy skills. Furthermore, phonological awareness was assessed in both groups, while in dyslexic participants also reading and writing performance was measured. We found significantly lower gamma peak frequencies as well as lower phonological awareness scores in dyslexic participants compared to age-matched controls. Additionally, results showed a positive correlation between the individual gamma frequency and phonological awareness. Our data suggest a hierarchical structure of neural gamma oscillations, phonological awareness, and literacy skills. Thereby, the results emphasize altered gamma oscillation not only as a core deficit in dyslexia but also as a potential target for future causal interventions. We discuss these findings considering non-invasive brain stimulation techniques and suggest transcranial alternating current stimulation as a promising approach to normalize dysfunctional oscillations in dyslexia.

Interaction of Background Noise and Auditory Hallucinations on Phonemic Mismatch Negativity (MMN) and P3a Processing in Schizophrenia

Auditory hallucinations (AHs) are among the cardinal symptoms of schizophrenia (SZ). During the presence of AHs aberrant activity of auditory cortices have been observed, including hyperactivation during AHs alone and hypoactivation when AHs are accompanied by a concurrent external auditory competitor. Mismatch negativity (MMN) and P3a are common ERPs of interest within the study of SZ as they are robustly reduced in the chronic phase of the illness. The present study aimed to explore whether background noise altered the auditory MMN and P3a in those with SZ and treatment-resistant AHs.

METHODS

MMN and P3a were assessed in 12 hallucinating patients (HPs), 11 non-hallucinating patients (NPs) and 9 healthy controls (HCs) within an auditory oddball paradigm. Standard (P = 0.85) and deviant (P = 0.15) stimuli were presented during three noise conditions: silence (SL), traffic noise (TN), and wide-band white noise (WN).

RESULTS

HPs showed significantly greater deficits in MMN amplitude relative to NPs in all background noise conditions, though predominantly at central electrodes. Conversely, both NPs and HPs exhibited significant deficits in P3a amplitude relative to HCs under the SL condition only.

SIGNIFICANCE

These findings suggest that the presence of AHs may specifically impair the MMN, while the P3a appears to be more generally impaired in SZ. That MMN amplitudes are specifically reduced for HPs during background noise conditions suggests HPs may have a harder time detecting changes in phonemic sounds during situations with external traffic or "real-world" noise compared to NPs.