Speech Lateralization Research Articles

Neuroanatomical correlates of musicianship in left-handers

BackgroundLeft-handedness is a condition that reverses the typical left cerebral dominance of motor control to an atypical right dominance. The impact of this distinct control — and its associated neuroanatomical peculiarities — on other cognitive functions such as music processing or playing a musical instrument remains unexplored. Previous studies in right-handed population have linked musicianship to a larger volume in the (right) auditory cortex and a larger volume in the (right) arcuate fasciculus.ResultsIn our study, we reveal that left-handed musicians (n = 55), in comparison to left-handed non-musicians (n = 75), exhibit a larger gray matter volume in both the left and right Heschl’s gyrus, critical for auditory processing. They also present a higher number of streamlines across the anterior segment of the right arcuate fasciculus. Importantly, atypical hemispheric lateralization of speech (notably prevalent among left-handers) was associated to a rightward asymmetry of the AF, in contrast to the leftward asymmetry exhibited by the typically lateralized.ConclusionsThese findings suggest that left-handed musicians share similar neuroanatomical characteristics with their right-handed counterparts. However, atypical lateralization of speech might potentiate the right audiomotor pathway, which has been associated with musicianship and better musical skills. This may help explain why musicians are more prevalent among left-handers and shed light on their cognitive advantages.

Reduced Neural Specialization for Word-level Linguistic Prosody in Children with Autism.

Children with autism often show atypical brain lateralization for speech and language processing, however, it is unclear what linguistic component contributes to this phenomenon. Here we measured event-related potential (ERP) responses in 21 school-age autistic children and 25 age-matched neurotypical (NT) peers during listening to word-level prosodic stimuli. We found that both groups displayed larger late negative response (LNR) amplitude to native prosody than to nonnative prosody; however, unlike the NT group exhibiting left-lateralized LNR distinction of prosodic phonology, the autism group showed no evidence of LNR lateralization. Moreover, in both groups, the LNR effects were only present for prosodic phonology but not for phoneme-free prosodic acoustics. These results extended the findings of inadequate neural specialization for language in autism to sub-lexical prosodic structures.

Hand Preference in Children’s Referential Gestures During Storytelling: Testing for Effects of Bilingualism, Language Ability, Age, and Sex

Adults, preschool children, and infants gesture more with their right hand than with their left hand. Since gestures and speech are related in production, it is possible that this right-hand preference reflects left-hemisphere lateralization for gestures and speech. The primary purpose of the present study was to test if children between the ages of 6 and 10 years show a right-hand preference in referential gestures while telling a story. We also tested four predictors of children’s degree of right-hand preference: 1) bilingualism, 2) language proficiency, 3) age, and 4) sex. Previous studies have shown that these variables are related to the degree of speech lateralization. Twenty-five English monolingual (17 girls; Mage = 8.0, SDage = 1.4), 21 French monolingual (12 girls; Mage = 7.3, SDage = 1.4,) and 25 French-English bilingual (11 girls; Mage = 8.5, SDage = 1.4) children watched a cartoon and told the story back. The bilinguals did this once in each language. The referential gestures were coded for handedness. Most of the participants showed a right-hand preference for gesturing. In English, none of the predictor variables was clearly related to right-hand preference. In French, the monolinguals showed a stronger right-hand preference than the bilinguals. These inconsistent findings across languages raise doubts as to whether the right-hand preference is linked to lateralization for speech.

Developmental changes in the brain response to speech during the first year of life: A near-infrared spectroscopy study of dutch-learning infants

Language acquisition in the first year of life plays an important role in human development. Although recent research has increased our knowledge of early language development, the origins and developmental trajectories of language processing during infancy are still being debated. One important issue is whether the infant brain has already developed adult-like functional cortical specialization and lateralization for speech and language processing. Although a relatively large number of previous studies have investigated the cortical specialization for speech processing in newborns by comparing responses to normal speech with responses to time-reversed speech as a control, the subsequent development of this differential response is less well understood. In the current study, our primary goal was, therefore, to expand our knowledge of functional specialization for speech during the first year of life. By using functional near-infrared spectroscopy (fNIRS), we examined the hemodynamic responses in the temporal cortex to forward-going speech in the native language, Dutch, and backward Dutch in seventy-eight infants aged 5 and 10 months. We observed that five-month-old infants show bilateral activation to both forward and backward speech without obvious hemispheric lateralization for language, while ten-month-old infants show greater left-lateralized inverted responses (e.g., reduction in oxyhaemoglobin and increase in deoxyhaemoglobin) to forward speech than to backward speech. Overall, our findings indicate that the neural correlates of language processing undergo developmental changes in the first year of life.

Латерализация слухоречевой асимметрии при афазических расстройствах и ее влияние на эффективность дихотического прослушивания серий односложных слов и динамику восстановления речи

The dichotic listening task is commonly used in a wide range of neuropsychological issues for studying interhemispheric asymmetry and interhemispheric interaction mechanisms. The article aims to determine the specific vector of auditory speech asymmetry for efferent motor and acoustic mnestic aphasia and its correlation with the dynamics of speech recovery. The paper studied the frequency of the right and left vectors of auditory speech asymmetry in aphasics with different time post-onset and structural characteristics of lesions. Also, the paper analyses the influence of the ear advantage side on the efficiency index of dichotic listening and quantitative indicators of speech. Material. Patients with acoustic mnestic (n = 52) and efferent motor aphasia (N = 58) of moderate and mild severity. Methods. The dichotic listening task: 16 paired series of 4 monosyllabic words in each. Results. Time post-onset, as well as lesion size, does not influence directly auditory speech laterality in aphasics. The frequency of occurrence of the positive and negative signs of the coefficient of the right ear has no pronounced differences between the different lesion sizes and time post-onset in aphasia. The left hemisphere lesion marks the impairment of the reciprocity in hemispheric interaction. The left ear advantage influences positively the dichotic listening efficiency index. Aphasia recovery does not have a direct conjugacy with the side of lesion or ear advantage. At the same time, the left ear advantage in acoustic mnestic aphasia creates a more pronounced “positive shift” in speech scores than in efferent motor aphasia. Conclusion. It appears that interhemispheric speech reorganization is determined apart from topical, typological, time post-onset and the left-handedness factors by others that needed to be investigated.

The perversion of language: Jules Baillarger on aphasia, the lateralization of speech, and the Baillarger-Jackson principle

ABSTRACT Jules Baillarger was one of the foremost figures of nineteenth-century neurobiology. He is remembered today for his discovery that the human cerebral cortex is composed of six intercalated layers. Even today, two horizontal fiber bundles within cortical layers IV and V are referred to as the outer and inner bands of Baillarger. It is a measure of the importance of Baillarger’s discovery that his findings were elaborated upon with advances in microscopy and the development of methods for staining neurons and myelin by, notably, Theodor Meynert and Santiago Ramon y Cajal. Furthermore, Baillarger’s observation that there are variations in the thickness of one or another of the six cortical layers in different cortical regions, and the discovery of giant pyramidal motor neurons in layer V of the precentral gyrus, ultimately led to the cytoarchitectonic and myeloarchitectonic maps of Oscar Vogt and Cécile Vogt-Mugnier, and of their student Korbinian Brodmann (1908). Less well known are Baillarger’s contributions to the semiology of aphasia and the pivotal role he played in the recognition of the localization and lateralization of speech to the left hemisphere. Paul Broca’s localization of articulate language to the posterior aspect of the frontal lobes and Marc Dax’s discovery that speech is a function of the left hemisphere were vigorously challenged within French academic medicine until 1865, when Baillarger gave two addresses to the Royal Academy of Medicine. In the first address, he described a form of aphasia he called the perversion of language, which we now call fluent aphasia, and reported that aphasic patients can express words or parts of sentences when they are angry or excited, a phenomenon now known as the Baillarger-Jackson principle. In his second address, Baillarger supported the lateralization of speech to the left hemisphere of the brain and referred to this association as Dax’s “singular law,” and supported the localization of speech to the posterior aspect of the left inferior frontal gyrus. Baillarger’s description of the perversion of language and of the influence of emotions on speech presaged the discipline of aphasiology, and his support for the lateralization of speech to the left hemisphere marks the first instance of the unequivocal recognition of asymmetrical hemispheric functions by academic medicine. This article reviews these aspects of Baillargher’s career. Critical sections of his papers on cortical structure, aphasia, and functional hemispheric asymmetry are translated by the author.

The relationship between lateralization patterns from sequence based motor tasks and hemispheric speech dominance.

Objective: Skilled motor praxis and speech production display marked asymmetries at the individual and the population level, favoring the right hand and the left hemisphere, respectively. Theories suggesting a common processing mechanism between praxis and speech are supported by evidence that shared neural architecture underlies both functions. Despite advances in understanding the neurobiology of this left-hemisphere specialization the cortical networks linking these 2 functions are rarely investigated on a behavioral level. Method: This study deploys functional transcranial doppler (fTCD) ultrasound to directly measure hemispheric activation during skilled manual praxis tasks shown to be correlated to hemispheric speech lateralization indices. In a new paradigm we test the hypothesis that praxis tasks are highly dependent on the left hemisphere's capacity for processing sequential information will be better correlated with direction and strength of hemispheric speech lateralization. Results: Across 2 experiments we first show that only certain praxis tasks (pegboard and coin-rotation) correlated with direct measurements of speech lateralization despite shared properties across all tasks tested. Second, through novel imaging of hemispheric activation during praxis, results showed that the pegboard differed in the lateralization pattern created and furthermore that it was significantly related to speech laterality indices, which was not the case for either of the other two tasks. Conclusion: These results are discussed in terms of a lateralized speech-praxis control mechanism and demonstrates that measurements of motor paradigms through the use of fTCD are reliable enough to provide a new insight to the behavioral relationship been speech and handedness. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Lateralization in the dichotic listening of tones is influenced by the content of speech

Cognitive functions, for example speech processing, are distributed asymmetrically in the two hemispheres that mostly have homologous anatomical structures. Dichotic listening is a well-established paradigm to investigate hemispherical lateralization of speech. However, the mixed results of dichotic listening, especially when using tonal languages as stimuli, complicates the investigation of functional lateralization. We hypothesized that the inconsistent results in dichotic listening are due to an interaction in processing a mixture of acoustic and linguistic attributes that are differentially processed over the two hemispheres. In this study, a within-subject dichotic listening paradigm was designed, in which different levels of speech and linguistic information was incrementally included in different conditions that required the same tone identification task. A left ear advantage (LEA), in contrast with the commonly found right ear advantage (REA) in dichotic listening, was observed in the hummed tones condition, where only the slow frequency modulation of tones was included. However, when phonemic and lexical information was added in simple vowel tone conditions, the LEA became unstable. Furthermore, ear preference became balanced when phonological and lexical-semantic attributes were included in the consonant-vowel (CV), pseudo-word, and word conditions. Compared with the existing REA results that use complex vowel word tones, a complete pattern emerged gradually shifting from LEA to REA. These results support the hypothesis that an acoustic analysis of suprasegmental information of tones is preferably processed in the right hemisphere, but is influenced by phonological and lexical semantic processes residing in the left hemisphere. The ear preference in dichotic listening depends on the levels of speech and linguistic analysis and preferentially lateralizes across the different hemispheres. That is, the manifestation of functional lateralization depends on the integration of information across the two hemispheres.

Is it possible to detect cerebral dominance via EEG signals by using deep learning?

Each brain hemisphere is dominant for certain functions such as speech. The determination of speech laterality prior to surgery is of paramount importance for accurate risk prediction. In this study, we aimed to determine speech laterality via EEG signals by using noninvasive machine learning techniques. The retrospective study included 67 subjects aged 18–65 years who had no chronic diseases and were diagnosed as healthy based on EEG examination. The subjects comprised 35 right-hand dominant (speech center located in the left hemisphere) and 32 left-hand dominant individuals (speech center located in the right hemisphere). A spectrogram was created for each of the 18 EEG channels by using various Convolutional Neural Networks (CNN) architectures including VGG16, VGG19, ResNet, MobileNet, NasNet, and DenseNet. These architectures were used to extract features from the spectrograms. The extracted features were classified using Support Vector Machines (SVM) and the classification performances of the CNN models were evaluated using Area Under the Curve (AUC). Of all the CNN models used in the study, VGG16 had a higher AUC value (0.83 ± 0.05) in the determination of speech laterality compared to all other models. The present study is a pioneer investigation into the determination of speech laterality via EEG signals with machine learning techniques, which, to our knowledge, has never been reported in the literature. Moreover, the classification results obtained in the study are promising and lead the way for subsequent studies though not practically feasible.

Altered hemispheric specialization for speech in adult dyslexic readers: An ERPs and dichotic listening study

Abstract The aim of this study was to investigate the functional speech lateralization in adult dyslexic readers whose native language is Hebrew. Event-related potentials (ERPs) were recorded from 22 non-impaired readers and 18 dyslexic readers performing dichotic nonsense consonant-vowel (CV) syllables and dichotic vowels target detection tasks. Evidence of altered patterns of behavioral speech lateralization was found in the dyslexic group mainly for the CV syllables task. The latencies and amplitudes of the N1 P2 ERPs complex produced by the dichotic CV syllables and dichotic vowels tasks were deviant as well. The findings suggest a differently organized auditory system with altered speech lateralization in adult dyslexic readers.

Speech lateralization and motor control.

A relationship between motor control and speech lateralization has long been postulated by researchers and clinicians with an interest in the functional organization of the human brain. Exactly how motor control might be related to speech representation, however, is rarely examined. This chapter examines current issues relating to the organization, development, and measurement of motor control and speech representation. We further consider from neuropsychological, developmental, neurological, and genetic perspectives that speech and fine motor control involve planning and sequencing processes, which are mediated by an integrated neural network localized to the left hemisphere. Specifically, we discuss studies from our laboratory using functional transcranial Doppler ultrasonography to determine speech laterality, correlating this with hand preference and pegboard measures of motor laterality. Our findings show that handedness, as measured by a motor skill task, can be predictive of speech laterality, both in typically developing adults and children. We have also shown that individuals with developmental motor coordination impairments also show atypical speech lateralization, providing further evidence that neurological motor and speech systems are intrinsically connected. We consider these results in the context of a left-lateralized speech-praxis center model, which could account for the relationship shown between sequence-based motor and speech tasks.

Dopamine drives left-hemispheric lateralization of neural networks during human speech.

Although the concept of left-hemispheric lateralization of neural processes during speech production has been known since the times of Broca, its physiological underpinnings still remain elusive. We sought to assess the modulatory influences of a major neurotransmitter, dopamine, on hemispheric lateralization during real-life speaking using a multimodal analysis of functional MRI, intracranial EEG recordings, and large-scale neural population simulations based on diffusion-weighted MRI. We demonstrate that speech-induced phasic dopamine release into the dorsal striatum and speech motor cortex exerts direct modulation of neuronal activity in these regions and drives left-hemispheric lateralization of speech production network. Dopamine-induced lateralization of functional activity and networks during speaking is not dependent on lateralization of structural nigro-striatal and nigro-motocortical pathways. Our findings provide the first mechanistic explanation for left-hemispheric lateralization of human speech that is due to left-lateralized dopaminergic modulation of brain activity and functional networks.

Atypical Callosal Morphology in Children with Speech Sound Disorder

Speech sound disorder (SSD) is common, yet its neurobiology is poorly understood. Recent studies indicate atypical structural and functional anomalies either in one hemisphere or both hemispheres, which might be accompanied by alterations in inter-hemispheric connectivity. Indeed, abnormalities of the corpus callosum – the main fiber tract connecting the two hemispheres – have been linked to speech and language deficits in associated disorders, such as stuttering, dyslexia, aphasia, etc. However, there is a dearth of studies examining the corpus callosum in SSD. Here, we investigated whether a sample of 18 children with SSD differed in callosal morphology from 18 typically developing children carefully matched for age. Significantly reduced dimensions of the corpus callosum, particularly in the callosal anterior third, were observed in children with SSD. These findings indicating pronounced callosal aberrations in SSD make an important contribution to an understudied field of research and may suggest that SSD is accompanied by atypical lateralization of speech and language function.

Auditory dysfunction in patients with Huntington’s disease

ObjectiveHuntington’s disease (HD) is an autosomal, dominantly inherited, neurodegenerative disease. The main clinical features are motor impairment, progressive cognitive deterioration and behavioral changes. The aim of our study was to find out whether patients with HD suffer from disorders of the auditory system. MethodsA group of 17 genetically verified patients (11 males, 6 females) with various stages of HD (examined by UHDRS – motor part and total functional capacity, MMSE for cognitive functions) underwent an audiological examination (high frequency pure tone audiometry, otoacoustic emissions, speech audiometry, speech audiometry in babble noise, auditory brainstem responses). Additionally, 5 patients underwent a more extensive audiological examination, focused on central auditory processing. The results were compared with a group of age-matched healthy volunteers. ResultsOur results show that HD patients have physiologic hearing thresholds, otoacoustic emissions and auditory brainstem responses; however, they display a significant decrease in speech understanding, especially under demanding conditions (speech in noise) compared to age-matched controls. Additional auditory tests also show deficits in sound source localization, based on temporal and intensity cues. We also observed a statistically significant correlation between the perception of speech in noise, and motoric and cognitive functions. However, a correlation between genetic predisposition (number of triplets) and function of inner ear was not found. ConclusionsWe conclude that HD negatively influences the function of the central part of the auditory system at cortical and subcortical levels, altering predominantly speech processing and sound source lateralization. SignificanceWe have thoroughly characterized auditory pathology in patients with HD that suggests involvement of central auditory and cognitive areas.

Hemispheric speech lateralisation in the developing brain is related to motor praxis ability

Commonly displayed functional asymmetries such as hand dominance and hemispheric speech lateralisation are well researched in adults. However there is debate about when such functions become lateralised in the typically developing brain. This study examined whether patterns of speech laterality and hand dominance were related and whether they varied with age in typically developing children. 148 children aged 3–10 years performed an electronic pegboard task to determine hand dominance; a subset of 38 of these children also underwent functional Transcranial Doppler (fTCD) imaging to derive a lateralisation index (LI) for hemispheric activation during speech production using an animation description paradigm. There was no main effect of age in the speech laterality scores, however, younger children showed a greater difference in performance between their hands on the motor task. Furthermore, this between-hand performance difference significantly interacted with direction of speech laterality, with a smaller between-hand difference relating to increased left hemisphere activation. This data shows that both handedness and speech lateralisation appear relatively determined by age 3, but that atypical cerebral lateralisation is linked to greater performance differences in hand skill, irrespective of age. Results are discussed in terms of the common neural systems underpinning handedness and speech lateralisation.

Phonetic detail and lateralization of reading-related inner speech and of auditory and somatosensory feedback processing during overt reading.

Phonetic detail and lateralization of inner speech during covert sentence reading as well as overt reading in 32 right-handed healthy participants undergoing 3T fMRI were investigated. The number of voiceless and voiced consonants in the processed sentences was systematically varied. Participants listened to sentences, read them covertly, silently mouthed them while reading, and read them overtly. Condition comparisons allowed for the study of effects of externally versus self-generated auditory input and of somatosensory feedback related to or independent of voicing. In every condition, increased voicing modulated bilateral voice-selective regions in the superior temporal sulcus without any lateralization. The enhanced temporal modulation and/or higher spectral frequencies of sentences rich in voiceless consonants induced left-lateralized activation of phonological regions in the posterior temporal lobe, regardless of condition. These results provide evidence that inner speech during reading codes detail as fine as consonant voicing. Our findings suggest that the fronto-temporal internal loops underlying inner speech target different temporal regions. These regions differ in their sensitivity to inner or overt acoustic speech features. More slowly varying acoustic parameters are represented more anteriorly and bilaterally in the temporal lobe while quickly changing acoustic features are processed in more posterior left temporal cortices. Furthermore, processing of external auditory feedback during overt sentence reading was sensitive to consonant voicing only in the left superior temporal cortex. Voicing did not modulate left-lateralized processing of somatosensory feedback during articulation or bilateral motor processing. This suggests voicing is primarily monitored in the auditory rather than in the somatosensory feedback channel. Hum Brain Mapp 38:493-508, 2017. © 2016 Wiley Periodicals, Inc.

The mane effect in the horse (Equus ferus caballus): Right mane dominance enhanced in mares but not associated with left and right manoeuvres in a reining competition

ABSTRACTA human physical asymmetry is the near 90% clockwise occipitoparietal scalp hair-whorl direction in Europeans, an incidence that approximates the left lateralization of speech and right-handedness. Hair-whorl direction is also asymmetric in horses, Equus ferus caballus and placement is proposed to be related to temperament and lateralized skill in equitation manoeuvres. We describe a hair-whorl asymmetry in the horse, mane direction. Of 526, 3-year-old American Quarter horses, 69% of horses had mane directed to the right and 31% had mane directed to the left. The bias was larger in females, with 74% of females vs. 65% of males having mane directed to the right. Mane direction was unrelated to coat colour. The behavioural significance of mane asymmetry was investigated using judges’ scores from a reining competition requiring symmetrical maneuvers of spin, circle and roll-back to either the left or to the right. There was no relation between mane asymmetry and overall reining performance and no relation between mane direction and scores for left or right manoeuvres. The results are discussed in relation to the significance of morphological asymmetries, neural function and the influence of planar cell polarity genes, such as Frizzled, that influence epidermal hair cell patterning.

Speech mapping using depth electrodes: The “electric Wada”

ObjectivesThe Wada test is the gold standard for identification of the side of speech dominance but is associated with risk of angiography and requires patient cooperation. We report a method to verify speech laterality using implanted electrodes in patients undergoing stereo-encephalography (SEEG). Patients and methodsFour pediatric patients with frontal lobe drug-resistant epilepsy underwent implantation of multiple SEEG electrodes using framed stereotaxy to identify the epileptogenic zone, including electrodes placed bilaterally into the pars opercularis of each inferior frontal gyrus from a superior parasagittal entry point. Biphasic stimulation at 50Hz, 0.3ms pulse width, up to 10mA was administered to distal contacts during a reading task. ResultsSpeech arrest upon stimulation was obtained when stimulating distal contacts in the inferior frontal gyrus on one side with no effect on the contralateral side, establishing language laterality in every patient. This information was used to plan subsequent surgical treatment. There were no adverse events of implantation or stimulation. ConclusionsBrain mapping using SEEG electrodes is feasible and can be used to lateralize speech dominance. In cases of frontal lobe epilepsy in which electrodes will be implanted bilaterally for recording of ictal activity, this technique may make the Wada test unnecessary.

Atypical speech lateralization in adults with developmental coordination disorder demonstrated using functional transcranial Doppler ultrasound.

Research using clinical populations to explore the relationship between hemispheric speech lateralization and handedness has focused on individuals with speech and language disorders, such as dyslexia or specific language impairment (SLI). Such work reveals atypical patterns of cerebral lateralization and handedness in these groups compared to controls. There are few studies that examine this relationship in people with motor coordination impairments but without speech or reading deficits, which is a surprising omission given the prevalence of theories suggesting a common neural network underlying both functions. We use an emerging imaging technique in cognitive neuroscience; functional transcranial Doppler (fTCD) ultrasound, to assess whether individuals with developmental coordination disorder (DCD) display reduced left‐hemisphere lateralization for speech production compared to control participants. Twelve adult control participants and 12 adults with DCD, but no other developmental/cognitive impairments, performed a word‐generation task whilst undergoing fTCD imaging to establish a hemispheric lateralization index for speech production. All participants also completed an electronic peg‐moving task to determine hand skill. As predicted, the DCD group showed a significantly reduced left lateralization pattern for the speech production task compared to controls. Performance on the motor skill task showed a clear preference for the dominant hand across both groups; however, the DCD group mean movement times were significantly higher for the non‐dominant hand. This is the first study of its kind to assess hand skill and speech lateralization in DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance. This fits alongside previous work showing atypical cerebral lateralization in DCD for other cognitive processes (e.g., executive function and short‐term memory) and thus speaks to debates on theories of the links between motor control and language production.

Risk Factors Associated With Language in Autism Spectrum Disorder: Clues to Underlying Mechanisms.

Identifying risk factors associated with neurodevelopmental disorders is an important line of research, as it will lead to earlier identification of children who could benefit from interventions that support optimal developmental outcomes. The primary goal of this review was to summarize research on risk factors associated with autism spectrum disorder (ASD). The review focused on studies of infants who have older siblings with ASD, with particular emphasis on risk factors associated with language impairment that affects the majority of children with ASD. Findings from this body of work were compared to the literature on specific language impairment. A wide range of risk factors has been found for ASD, including demographic (e.g., male, family history), behavioral (e.g., gesture, motor) and neural risk markers (e.g., atypical lateralization for speech and reduced functional connectivity). Environmental factors, such as caregiver interaction, have not been found to predict language outcomes. Many of the risk markers for ASD are also found in studies of risk for specific language impairment, including demographic, behavioral, and neural factors. There are significant gaps in the literature and limitations in the current research that preclude direct cross-syndrome comparisons. Future research directions are outlined that could address these limitations.