Speech-sound-selective auditory impairment in children with autism: they can perceive but do not attend

Deficient brainstem encoding of pitch in children with Autism Spectrum Disorders

OBJECTIVE

Deficient prosody is a hallmark of the pragmatic (socially contextualized) language impairment in Autism Spectrum Disorders (ASD). Prosody communicates emotion and intention and is conveyed through acoustic cues such as pitch contour. Thus, the objective of this study was to examine the subcortical representations of prosodic speech in children with ASD.

METHODS

Using passively evoked brainstem responses to speech syllables with descending and ascending pitch contours, we examined sensory encoding of pitch in children with ASD who had normal intelligence and hearing and were age-matched with typically developing (TD) control children.

RESULTS

We found that some children on the autism spectrum show deficient pitch tracking (evidenced by increased Frequency and Slope Errors and reduced phase locking) compared with TD children.

CONCLUSIONS

This is the first demonstration of subcortical involvement in prosody encoding deficits in this population of children.

SIGNIFICANCE

Our findings may have implications for diagnostic and remediation strategies in a subset of children with ASD and open up an avenue for future investigations.

Linking social and vocal brains: could social segregation prevent a proper development of a central auditory area in a female songbird?

Direct social contact and social interaction affect speech development in human infants and are required in order to maintain perceptual abilities; however the processes involved are still poorly known. In the present study, we tested the hypothesis that social segregation during development would prevent the proper development of a central auditory area, using a "classical" animal model of vocal development, a songbird. Based on our knowledge of European starling, we raised young female starlings with peers and only adult male tutors. This ensured that female would show neither social bond with nor vocal copying from males. Electrophysiological recordings performed when these females were adult revealed perceptual abnormalities: they presented a larger auditory area, a lower proportion of specialized neurons and a larger proportion of generalist sites than wild-caught females, whereas these characteristics were similar to those observed in socially deprived (physically separated) females. These results confirmed and added to earlier results for males, suggesting that the degree of perceptual deficiency reflects the degree of social separation. To our knowledge, this report constitutes the first evidence that social segregation can, as much as physical separation, alter the development of a central auditory area.

Audio-vocal system regulation in children with autism spectrum disorders

Do children with autism spectrum disorders (ASD) respond similarly to perturbations in auditory feedback as typically developing (TD) children? Presentation of pitch-shifted voice auditory feedback to vocalizing participants reveals a close coupling between the processing of auditory feedback and vocal motor control. This paradigm was used to test the hypothesis that abnormalities in the audio-vocal system would negatively impact ASD compensatory responses to perturbed auditory feedback. Voice fundamental frequency (F(0)) was measured while children produced an /a/ sound into a microphone. The voice signal was fed back to the subjects in real time through headphones. During production, the feedback was pitch shifted (-100 cents, 200 ms) at random intervals for 80 trials. Averaged voice F(0) responses to pitch-shifted stimuli were calculated and correlated with both mental and language abilities as tested via standardized tests. A subset of children with ASD produced larger responses to perturbed auditory feedback than TD children, while the other children with ASD produced significantly lower response magnitudes. Furthermore, robust relationships between language ability, response magnitude and time of peak magnitude were identified. Because auditory feedback helps to stabilize voice F(0) (a major acoustic cue of prosody) and individuals with ASD have problems with prosody, this study identified potential mechanisms of dysfunction in the audio-vocal system for voice pitch regulation in some children with ASD. Objectively quantifying this deficit may inform both the assessment of a subgroup of ASD children with prosody deficits, as well as remediation strategies that incorporate pitch training.

Enhanced perceptual processing of speech in autism

Theories of autism have proposed that a bias towards low-level perceptual information, or a featural/surface-biased information-processing style, may compromise higher-level language processing in such individuals. Two experiments, utilizing linguistic stimuli with competing low-level/perceptual and high-level/semantic information, tested processing biases in children with autism and matched controls. Whereas children with autism exhibited superior perceptual processing of speech relative to controls, and showed no evidence of either a perceptual or semantic processing bias, controls showed a tendency to process speech semantically. The data provide partial support to the perceptual theories of autism. It is additionally proposed that the pattern of results may reflect different patterns of attentional focusing towards single or multiple stimulus cues in speech between children with autism and controls.

Electrophysiological signatures: magnetoencephalographic studies of the neural correlates of language impairment in autism spectrum disorders

While magnetoencephalography (MEG) is of increasing utility in the assessment of pediatric patients with seizure disorders, this reflects only a part of the clinical potential of the technology. Beyond epilepsy, a broad range of developmental psychiatric disorders require the spatial and temporal resolution of brain activity offered by MEG. This article reviews the application of MEG in the study of auditory processing as an aspect of language impairment in children. Specifically, the potential application of MEG is elaborated in autism spectrum disorders (ASD), a devastating disorder with prevalence of 1 in 150. Results demonstrate the sensitivity of MEG for detection of abnormalities of auditory processing in ASD ('electrophysiological signatures') and their clinical correlates. These findings offer promise for the comprehensive assessment of developmental neuropsychiatric disorders.

Auditory evoked fields predict language ability and impairment in children

Recent evidence suggests that a subgroup of children with autism show similarities to children with Specific Language Impairment (SLI) in the pattern of their linguistic impairments, but the source of this overlap is unclear. We examined the ability of auditory evoked magnetic fields to predict language and other developmental abilities in children and adolescents. Following standardized assessment of language ability, nonverbal IQ, and autism-associated behaviors, 110 trails of a tone were binaurally presented to 45 7-18 year olds who had typical development, autism (with LI), Asperger Syndrome (i.e., without LI), or SLI. Using a 151-channel MEG system, latency of left hemisphere (LH) and right hemisphere (RH) auditory M50 and M100 peaks was recorded. RH M50 latency (and to a lesser extent, RH M100 latency) predicted overall oral language ability, accounting for 36% of the variance. Nonverbal IQ and autism behavior ratings were not predicted by any of the evoked fields. Latency of the RH M50 was the best predictor of clinical LI (i.e., irrespective of autism diagnosis), and demonstrated 82% accuracy in predicting Receptive LI; a cutoff of 84.6 ms achieved 92% specificity and 70% sensitivity in classifying children with and without Receptive LI. Auditory evoked responses appear to reflect language functioning and impairment rather than non-specific brain (dys)function (e.g., IQ, behavior). RH M50 latency proved to be a relatively useful indicator of impaired language comprehension, suggesting that delayed auditory perceptual processing in the RH may be a key neural dysfunction underlying the overlap between subgroups of children with autism and SLI.

Understanding autism and related disorders: what has imaging taught us?

Structural imaging studies of autism have documented increased total brain volume and early acceleration in brain growth. Functional MR imaging (fMRI) studies in autism have also led to the view of autism as a disorder of cortical functioning in which functional connectivity or synchronization of brain regions and cortical activity are disturbed with atypical cortical specialization.

Clarifying the associations between language and social development in autism: a study of non-native phoneme recognition

Autism spectrum disorders (ASDs) are characterized by correlated deficiencies in social and language development. This study explored a fundamental aspect of auditory information processing (AIP) that is dependent on social experience and critical to early language development: the ability to compartmentalize close-sounding speech sounds into singular phonemes. We examined this ability by assessing whether close-sounding non-native language phonemes were more likely to be perceived as disparate sounds by school-aged children with high-functioning ASD (n = 27), than by unaffected control subjects (n = 35). No significant group differences were observed. Although earlier in autistic development there may exist qualitative deficits in this specific aspect of AIP, they are not an enduring characteristic of verbal school-aged children with ASD.

Effects of object complexity and type on the gaze behavior of children with pervasive developmental disorder

The looking behavior of children with pervasive developmental disorder (PDD) and age- and IQ-matched normal control children was studied using infrared oculography. Stimuli varying in complexity and topic were presented to test whether children with PDD have specific abnormalities in looking behavior to complex stimuli and/or to faces. All children showed more and longer fixations on the complex objects than on the simple objects, especially the complex nonsense figure, but group differences were not found. The results show no evidence for specific abnormalities in looking behavior to either faces or to complex stimuli in high functioning children with PDD.

The perception of invariant speech features in children with autism

We investigated whether the good pitch-discrimination abilities reported in individuals with autism have adverse effects on their speech perception by compromising their ability to extract invariant phonetic features from speech input. The MMN, a brain response reflecting sound-discrimination processes, was recorded from children with autism and their controls for phoneme-category and pitch changes in speech stimuli under two different conditions: (a) when all the other features of the standard and deviant stimuli were kept constant, and (b) when constant variation with respect to an irrelevant feature was introduced to the standard and deviant stimuli. Children with autism had enhanced MMNs for pitch changes in both conditions, as well as for phoneme-category changes in the constant-feature condition. However, when the phoneme-category changes occurred in phonemes having pitch variation, the MMN enhancement was abolished in autistic children. This suggests that children with autism lose their advantage in phoneme discrimination when the context of the stimuli is speech-like and requires abstracting invariant speech features from varying input.

Audiovisual speech integration and lipreading in autism

BACKGROUND

During speech perception, the ability to integrate auditory and visual information causes speech to sound louder and be more intelligible, and leads to quicker processing. This integration is important in early language development, and also continues to affect speech comprehension throughout the lifespan. Previous research shows that individuals with autism have difficulty integrating information, especially across multiple sensory domains.

METHODS

In the present study, audiovisual speech integration was investigated in 18 adolescents with high-functioning autism and 19 well-matched adolescents with typical development using a speech in noise paradigm. Speech reception thresholds were calculated for auditory only and audiovisual matched speech, and lipreading ability was measured.

RESULTS

Compared to individuals with typical development, individuals with autism showed less benefit from the addition of visual information in audiovisual speech perception. We also found that individuals with autism were significantly worse than those in the comparison group at lipreading. Hierarchical regression demonstrated that group differences in the audiovisual condition, while influenced by auditory perception and especially by lipreading, were also attributable to a unique factor, which may reflect a specific deficit in audiovisual integration.

CONCLUSIONS

Combined deficits in audiovisual speech integration and lipreading in individuals with autism are likely to contribute to ongoing difficulties in speech comprehension, and may also be related to delays in early language development.

Mismatch negativity in children with autism and typical development

Children with autism are often characterized as having abnormalities in auditory processing. This study examined automatic and active processing of simple auditory stimuli in children using a component of event related potentials, the mismatch negativity (MMN). Amplitude of MMN in children with autism was significantly smaller than in children with typical development in unattended conditions. However, children with autism exhibited a typical amplitude MMN when attending to the stimuli. Receptive language and MMN were not related in children with autism. Findings support the idea of abnormal automatic auditory processing by children with autism. Auditory discrimination of infrequent changes in streams of sounds appears to be accomplished through a different mechanism than in typical children, specifically through the investment of attention.

Auditory event-related potentials and cognitive function of preterm children at five years of age

OBJECTIVE

In our previous study, auditory event-related potentials (AERPs) in preterm 1-year-old children had a positive deflection at 150-350 ms that correlated positively with their 2-year neurodevelopmental outcome. In a study of the same subjects at age 5, our aim was to assess AERPs and their relationship to neuropsychological test results.

METHODS

Preterm small (SGA, n=13), appropriate for gestational age (AGA, n=15), and control (n=13) children were assessed with an Easy paradigm presenting a large frequency change accompanied with occasional novel sounds, and a Challenging paradigm presenting small frequency and duration changes with a rapid rate. The preterm children underwent neurocognitive tests.

RESULTS

Easy paradigm. The P1 response to frequency deviant was smaller and MMN larger in the preterm than in the control children. Challenging paradigm. The P1 response to standard, frequency, and duration deviants was smaller in the preterm than in the control children. The N2 response to frequency deviant was larger in the preterm than in the control children. AGA and SGA children had similar AERPs. The P1, N2, and MMN amplitudes correlated with verbal IQ and NEPSY language subtests.

CONCLUSIONS

Small P1 response(s) appears to be typical for preterm children.

SIGNIFICANCE

Small P1 response in preterm children may suggest altered primary auditory processing.

Brain abnormalities in language disorders and in autism

It has been speculated that autism and specific language impairment share common underlying neural substrates because of the overlap in language impairment issues and evidence suggesting parallels in other domains and implying a possible shared genetic risk. Anatomically the two sets of disorders have generally been studied using different methodologies, but when identical methodologies have been used substantial similarities have been noted. Functionally there is a growing body of literature suggesting sensory perception abnormalities that have parallels in both conditions and that may be upstream of language abnormalities. Finding upstream mechanisms that impact language and non-language abnormalities in autism and specific language impairment would impact the orientation taken by translational attempts to use science to design treatments.

Pre-attentive auditory sensory processing in autistic spectrum disorder. Are electromagnetic measurements telling us a coherent story?

Sensory processing is a crucial underpinning of the development of social cognition, a function which is compromised in variable degree in patients with pervasive developmental disorders (PDD). In this manuscript, we review some of the most recent and relevant contributions, which have looked at auditory sensory processing derangement in PDD. The variability in the clinical characteristics of the samples studied so far, in terms of severity of the associated cognitive deficits and associated limited compliance, underlying aetiology and demographic features makes a univocal interpretation arduous. We hypothesise that, in patients with severe mental deficits, the presence of impaired auditory sensory memory as expressed by the mismatch negativity could be a non-specific indicator of more diffuse cortical deficits rather than causally related to the clinical symptomatology. More consistent findings seem to emerge from studies on less severely impaired patients, in whom increased pitch perception has been interpreted as an indicator of increased local processing, probably as compensatory mechanism for the lack of global processing (central coherence). This latter hypothesis seems extremely attractive and future trials in larger cohorts of patients, possibly standardising the characteristics of the stimuli are a much-needed development. Finally, specificity of the role of the auditory derangement as opposed to other sensory channels needs to be assessed more systematically using multimodal stimuli in the same patient group.

Atypical pattern of discriminating sound features in adults with Asperger syndrome as reflected by the mismatch negativity

Asperger syndrome, which belongs to the autistic spectrum of disorders, is characterized by deficits of social interaction and abnormal perception, like hypo- or hypersensitivity in reacting to sounds and discriminating certain sound features. We determined auditory feature discrimination in adults with Asperger syndrome with the mismatch negativity (MMN), a neural response which is an index of cortical change detection. We recorded MMN for five different sound features (duration, frequency, intensity, location, and gap). Our results suggest hypersensitive auditory change detection in Asperger syndrome, as reflected in the enhanced MMN for deviant sounds with a gap or shorter duration, and speeded MMN elicitation for frequency changes.

Seeing the face through the eyes: a developmental perspective on face expertise

Most people are experts in face recognition. We propose that the special status of this particular body part in telling individuals apart is the result of a developmental process that heavily biases human infants and children to attend towards the eyes of others. We review the evidence supporting this proposal, including neuroimaging results and studies in developmental disorders, like autism. We propose that the most likely explanation of infants' bias towards eyes is the fact that eye gaze serves important communicative functions in humans.

Auditory cortical change detection in adults with Asperger syndrome

The present study investigated whether auditory deficits reported in children with Asperger syndrome (AS) are also present in adulthood. To this end, event-related potentials (ERPs) were recorded from adults with AS for duration, pitch, and phonetic changes in vowels, and for acoustically matched non-speech stimuli. These subjects had enhanced mismatch negativity (MMN) amplitudes particularly for pitch and duration deviants, indicating enhanced sound-discrimination abilities. Furthermore, as reflected by the P3a, their involuntary orienting was enhanced for changes in non-speech sounds, but tended to be deficient for changes in speech sounds. The results are consistent with those reported earlier in children with AS, except for the duration-MMN, which was diminished in children and enhanced in adults.

Assessment of Stimulus Overselectivity with Tactile Compound Stimuli in Children with Autism

Autistic and typical children mastered a simultaneous discrimination task with three sets of all-tactile compound stimuli. During training, responding to one stimulus (S+) resulted in rewards whereas responding to the alternative (S-) was extinguished. Test 1 was conducted with recombinations of S+ and S- elements. In Test 2, the test stimulus to which the child responded most in Test 1 was pitched against the training S+. In Test 1, all children responded exclusively to one test probe, spuriously implying stimulus overselectivity in both populations. However, in Test 2, the typical children responded mostly to the training S+ indicating control by both S+ elements; the autistic children responded to both stimuli indicating reduced control by the second S+ element (indicating overselectivity).

Auditory characteristics of children with autism

OBJECTIVES

The objectives of this study were (1) to describe the auditory characteristics of children with autism relative to those of typically developing children and (2) to describe the test-retest reliability of behavioral auditory test measures with this population of children with autism.

DESIGN

Audiometric data were obtained from 22 children diagnosed with autism and 22 of their typically developing peers. The audiologic test battery consisted of behavioral measures (i.e., visual reinforcement audiometry, tangible reinforcement operant conditioning audiometry, and conditioned play audiometry) and physiological measures (auditory brain stem response audiometry, distortion product otoacoustic emissions, and acoustic reflexes).

RESULTS

Children with autism had physiologic test results equivalent to their typically developing counterparts. That is, no differences in auditory brain stem response audiometry, distortion product otoacoustic emissions, or acoustic reflex results were noted between the children with autism and typically developing children. However, behavioral measures revealed that about half of the children diagnosed with autism presented pure-tone averages outside of normal limits (i.e., >20 dB HL), although their response thresholds to speech were within normal limits. All behavioral test results were within normal limits (i.e., </=20 dB HL) for the typically developing children. In addition, test-retest variability was typically 15 dB or greater for children with autism as compared with variability of 10 dB or less for most of the typically developing children.

CONCLUSIONS

Children with autism demonstrated essentially equivalent results on a battery of physiological auditory tests as those obtained from typically developing children. However, on average, behavioral responses of children with autism were elevated and less reliable relative to those of typically developing children. Furthermore, approximately half of the children with autism demonstrated behavioral pure-tone averages outside of the normal hearing range (i.e., >20 dB HL) despite having normal to near-normal hearing sensitivity as determined by other audiometric measures.

Can spectro-temporal complexity explain the autistic pattern of performance on auditory tasks?

To test the hypothesis that level of neural complexity explain the relative level of performance and brain activity in autistic individuals, available behavioural, ERP and imaging findings related to the perception of increasingly complex auditory material under various processing tasks in autism were reviewed. Tasks involving simple material (pure tones) and/or low-level operations (detection, labelling, chord disembedding, detection of pitch changes) show a superior level of performance and shorter ERP latencies. In contrast, tasks involving spectrally- and temporally-dynamic material and/or complex operations (evaluation, attention) are poorly performed by autistics, or generate inferior ERP activity or brain activation. Neural complexity required to perform auditory tasks may therefore explain pattern of performance and activation of autistic individuals during auditory tasks.

Auditory perception and attention as reflected by the brain event-related potentials in children with Asperger syndrome

OBJECTIVE

Language development is delayed and deviant in individuals with autism, but proceeds quite normally in those with Asperger syndrome (AS). We investigated auditory-discrimination and orienting in children with AS using an event-related potential (ERP) paradigm that was previously applied to children with autism.

METHODS

ERPs were measured to pitch, duration, and phonetic changes in vowels and to corresponding changes in non-speech sounds. Active sound discrimination was evaluated with a sound-identification task.

RESULTS

The mismatch negativity (MMN), indexing sound-discrimination accuracy, showed right-hemisphere dominance in the AS group, but not in the controls. Furthermore, the children with AS had diminished MMN-amplitudes and decreased hit rates for duration changes. In contrast, their MMN to speech pitch changes was parietally enhanced. The P3a, reflecting involuntary orienting to changes, was diminished in the children with AS for speech pitch and phoneme changes, but not for the corresponding non-speech changes.

CONCLUSIONS

The children with AS differ from controls with respect to their sound-discrimination and orienting abilities.

SIGNIFICANCE

The results of the children with AS are relatively similar to those earlier obtained from children with autism using the same paradigm, although these clinical groups differ markedly in their language development.

Autism at the beginning: microstructural and growth abnormalities underlying the cognitive and behavioral phenotype of autism

Autistic symptoms begin in the first years of life, and recent magnetic resonance imaging studies have discovered brain growth abnormalities that precede and overlap with the onset of these symptoms. Recent postmortem studies of the autistic brain provide evidence of cellular abnormalities and processes that may underlie the recently discovered early brain overgrowth and arrest of growth that marks the first years of life in autism. Alternative origins and time tables for these cellular defects and processes are discussed. These cellular and growth abnormalities are most pronounced in frontal, cerebellar, and temporal structures that normally mediate the development of those same higher order social, emotional, speech, language, speech, attention, and cognitive functions that characterize autism. Cellular and growth pathologies are milder and perhaps nonexistent in other structures (e.g., occipital cortex), which are known to mediate functions that are often either mildly affected or entirely unaffected in autistic patients. It is argued that in autism, higher order functions largely fail to develop normally in the first place because frontal, cerebellar, and temporal cellular and growth pathologies occur prior to and during the critical period when these higher order neural systems first begin to form their circuitry. It is hypothesized that microstructural maldevelopment results in local and short distance overconnectivity in frontal cortex that is largely ineffective and in a failure of long-distance cortical-cortical coupling, and thus a reduction in frontal-posterior reciprocal connectivity. This altered circuitry impairs the essential role of frontal cortex in integrating information from diverse functional systems (emotional, sensory, autonomic, memory, etc.) and providing context-based and goal-directed feedback to lower level systems.

Advances in autism neuroimaging research for the clinician and geneticist

This review focuses on recent advances in the in vivo study of the whole brain in idiopathic autism. The brain is abnormally large in some but not all children with autism during post-natal development. Age-related changes in brain volume in autism are complex and appear to be abnormal from infancy into adulthood. Diffuse differences in total and regional gray and white matter volumes are found. The volumetric abnormalities appear to follow anomalous, complex, and non-uniform developmental curves. Diffuse abnormalities of brain chemical concentrations, neural network anatomy, brain lateralization, intra- and inter-hemispheric morphologic and functional connectivity, and serotonin synthesis capacity are also found. Abnormalities of head growth are first apparent during infancy. Abnormalities of total brain volume, gray and white matter volumes, brain chemistry, serotonin synthesis, and brain electrophysiology are evident by early childhood. Currently, no method of brain imaging helps with diagnosis or treatment of idiopathic autism, but ongoing research aims to unravel the heterogeneity of autism and may provide future diagnostic tools that inform treatment.

Change detection in children with autism: An auditory event-related fMRI study

Autism involves impairments in communication and social interaction, as well as high levels of repetitive, stereotypic, and ritualistic behaviours, and extreme resistance to change. This latter dimension, whilst required for a diagnosis, has received less research attention. We hypothesise that this extreme resistance to change in autism is rooted in atypical processing of unexpected stimuli. We tested this using auditory event-related fMRI to determine regional brain activity associated with passive detection of infrequently occurring frequency-deviant and complex novel sounds in a no-task condition. Participants were twelve 10- to 15-year-old children with autism and a group of 12 age- and sex-matched healthy controls. During deviance detection, significant activation common to both groups was located in the superior temporal and inferior frontal gyri. During 'novelty detection', both groups showed activity in the superior temporal gyrus, the temporo-parietal junction, the superior and inferior frontal gyri, and the cingulate gyrus. Children with autism showed reduced activation of the left anterior cingulate cortex during both deviance and novelty detection. During novelty detection, children with autism also showed reduced activation in the bilateral temporo-parietal region and in the right inferior and middle frontal areas. This study confirms previous evidence from ERP studies of atypical brain function related to automatic change detection in autism. Abnormalities involved a cortical network known to have a role in attention switching and attentional resource distribution. These results throw light on the neurophysiological processes underlying autistic 'resistance to change'.

Annotation: what do we know about sensory dysfunction in autism? A critical review of the empirical evidence

BACKGROUND

Unusual responses to sensory stimuli are seen in many children with autism. Their presence was highlighted both in early accounts of autism and in more recent first-person descriptions. There is a widespread belief that sensory symptoms characterize autism and differentiate it from other disorders. This paper examines the empirical evidence for this assumption.

METHOD

All controlled experimental laboratory investigations published since 1960 were identified through systematic searches using Medline/PubMed and PsycInfo search engines. A total of 48 empirical papers and 27 theoretical or conceptual papers were reviewed.

RESULTS

Sensory symptoms are more frequent and prominent in children with autism than in typically developing children, but there is not good evidence that these symptoms differentiate autism from other developmental disorders. Certain groups, including children with fragile X syndrome and those who are deaf-blind, appear to demonstrate higher rates of sensory symptoms than children with autism. In reviewing the evidence relevant to two theories of sensory dysfunction in autism, over- and under-arousal theory, we find that there is very little support for hyper-arousal and failure of habituation in autism. There is more evidence that children with autism, as a group, are hypo-responsive to sensory stimuli, but there are also multiple failures to replicate findings and studies that demonstrate lack of group differences.

CONCLUSIONS

The use of different methods, the study of different sensory modalities, and the changing scientific standards across decades complicate interpretation of this body of work. We close with suggestions for future research in this area.

The discrimination of and orienting to speech and non-speech sounds in children with autism

The present study aimed to find out how different stages of cortical auditory processing (sound encoding, discrimination, and orienting) are affected in children with autism. To this end, auditory event-related potentials (ERP) were studied in 15 children with autism and their controls. Their responses were recorded for pitch, duration, and vowel changes in speech stimuli, and for corresponding changes in the non-speech counterparts of the stimuli, while the children watched silent videos and ignored the stimuli. The responses to sound repetition were diminished in amplitude in the children with autism, reflecting impaired sound encoding. The mismatch negativity (MMN), an ERP indexing sound discrimination, was enhanced in the children with autism as far as pitch changes were concerned. This is consistent with earlier studies reporting auditory hypersensitivity and good pitch-processing abilities, as well as with theories proposing enhanced perception of local stimulus features in individuals with autism. The discrimination of duration changes was impaired in these children, however. Finally, involuntary orienting to sound changes, as reflected by the P3a ERP, was more impaired for speech than non-speech sounds in the children with autism, suggesting deficits particularly in social orienting. This has been proposed to be one of the earliest symptoms to emerge, with pervasive effects on later development.

Similarities in the phenotype of the auditory neural substrate in children with Asperger syndrome and their parents

Asperger syndrome (AS) is a developmental disorder of brain function characterized by deficits in social interaction including difficulties in understanding emotional expressions. Children with AS share some of the behavioural characteristics with their parents and AS seems to run particularly in the male members of the same families. The aim of the present study was to determine whether similarities could be found between children with AS and their parents at central auditory processing. It was found that in children with AS the sound encoding, as reflected by the exogenous components of event-related potentials, was similarly abnormal as in both their mothers and fathers. However, their abnormal cortical auditory discrimination, as indexed by the prolonged latency of the mismatch negativity, resembled that of their fathers but not that of their mothers. The present results suggest that complex genetic mechanisms may contribute to auditory abnormalities encountered in children with AS.

Auditory abnormalities in autism: toward functional distinctions among findings

Recently, findings on a wide range of auditory abnormalities among individuals with autism have been reported. To date, functional distinctions among these varied findings are poorly established. Such distinctions should be of interest to clinicians and researchers alike given their potential therapeutic and experimental applications. This review suggests three general trends among these findings as a starting point for future analyses. First, studies of auditory perception of linguistic and social auditory stimuli among individuals with autism generally have found impaired perception versus normal controls. Such findings may correlate with impaired language and communication skills and social isolation observed among individuals with autism. Second, studies of auditory perception of pitch and music among individuals with autism generally have found enhanced perception versus normal controls. These findings may correlate with the restrictive and highly focused behaviors observed among individuals with autism. Third, findings on the auditory perception of non-linguistic, non-musical stimuli among autism patients resist any generalized conclusions. Ultimately, as some researchers have already suggested, the distinction between impaired global processing and enhanced local processing may prove useful in making sense of apparently discordant findings on auditory abnormalities among individuals with autism.

Delayed automatic detection of change in speech sounds in adults with autism: a magnetoencephalographic study

OBJECTIVE

Autism is a form of pervasive developmental disorder in which dysfunction in interpersonal relationships and communication is fundamental. This study evaluated neurophysiological abnormalities at the basic level of language processing, i.e. automatic change detection of speech and non-speech sounds, using magnetoencephalographic recording of mismatch response elicited by change in vowels and tones.

METHODS

The auditory magnetic mismatch field (MMF) was evaluated in 9 adults with autism and 19 control subjects using whole-head magnetoencephalography. The MMF in response to the duration change of a pure tone or vowel /a/ and that in response to across-phoneme change between vowels /a/ and /o/, were recorded.

RESULTS

The groups were not significantly different in MMF power under any conditions. However, the autism group showed a left-biased latency prolongation of the MMF particularly under the across-phoneme change condition, and this latency delay was significantly associated with greater symptom severity.

CONCLUSIONS

These results suggest that adults with autism are associated with delayed processing for automatic change detection of speech sounds. These electrophysiological abnormalities at the earliest level of information processing may contribute to the basis for language deficits observed in autism.

SIGNIFICANCE

These results provide the first evidence for delayed latency of phonetic MMF in adults with autism.

Long-Lasting Modulation by Stimulus Context in Primate Auditory Cortex

A sound embedded in an acoustic stream cannot be unambiguously segmented and identified without reference to its stimulus context. To understand the role of stimulus context in cortical processing, we investigated the responses of auditory cortical neurons to 2-sound sequences in awake marmosets, with a focus on stimulus properties other than carrier frequency. Both suppressive and facilitatory modulations of cortical responses were observed by using combinations of modulated tone and noise stimuli. The main findings are as follows. 1) Preceding stimuli could suppress or facilitate responses to succeeding stimuli for durations >1 s. These long-lasting effects were dependent on the duration, sound level, and modulation parameters of the preceding stimulus, in addition to the carrier frequency. They occurred regardless of whether the 2 stimuli were separated by a silent interval. 2) Suppression was often tuned such that preceding stimuli whose parameters were similar to succeeding stimuli produced the strongest suppression. However, the responses of many units could be suppressed, although often weaker, even when the 2 stimuli were dissimilar. In some cases, only a dissimilar preceding stimulus produced suppression in the responses to the succeeding stimulus. 3) In contrast to suppression, facilitation of responses to succeeding stimuli by the preceding stimulus was usually strongest when the 2 stimuli were dissimilar. 4) There was no clear correlation between the firing rate evoked by the preceding stimulus and the change in the firing rate evoked by the succeeding stimulus, indicating that the observed suppression was not simply a result of habituation or spike adaptation. These results demonstrate that persistent modulations of the responses of an auditory cortical neuron to a given stimulus can be induced by preceding stimuli. Decreases or increases of responses to the succeeding stimuli are dependent on the spectral, temporal, and intensity properties of the preceding stimulus. This indicates that cortical auditory responses to a sound are not static, but instead depend on the stimulus context in a stimulus-specific manner. The long-lasting impact of stimulus context and the prevalence of facilitation suggest that such cortical response properties are important for auditory processing beyond forward masking, such as for auditory streaming and segregation.

Links between social and linguistic processing of speech in preschool children with autism: behavioral and electrophysiological measures

Data on typically developing children suggest a link between social interaction and language learning, a finding of interest both to theories of language and theories of autism. In this study, we examined social and linguistic processing of speech in preschool children with autism spectrum disorder (ASD) and typically developing chronologically matched (TDCA) and mental age matched (TDMA) children. The social measure was an auditory preference test that pitted 'motherese' speech samples against non-speech analogs of the same signals. The linguistic measure was phonetic discrimination assessed with mismatch negativity (MMN), an event-related potential (ERP). As a group, children with ASD differed from controls by: (a) demonstrating a preference for the non-speech analog signals, and (b) failing to show a significant MMN in response to a syllable change. When ASD children were divided into subgroups based on auditory preference, and the ERP data reanalyzed, ASD children who preferred non-speech still failed to show an MMN, whereas ASD children who preferred motherese did not differ from the controls. The data support the hypothesis of an association between social and linguistic processing in children with ASD.

Subjective face recognition difficulties, aberrant sensibility, sleeping disturbances and aberrant eating habits in families with Asperger syndrome

BACKGROUND

The present study was undertaken in order to determine whether a set of clinical features, which are not included in the DSM-IV or ICD-10 for Asperger Syndrome (AS), are associated with AS in particular or whether they are merely a familial trait that is not related to the diagnosis.

METHODS

Ten large families, a total of 138 persons, of whom 58 individuals fulfilled the diagnostic criteria for AS and another 56 did not to fulfill these criteria, were studied using a structured interview focusing on the possible presence of face recognition difficulties, aberrant sensibility and eating habits and sleeping disturbances.

RESULTS

The prevalence for face recognition difficulties was 46.6% in individuals with AS compared with 10.7% in the control group. The corresponding figures for subjectively reported presence of aberrant sensibilities were 91.4% and 46.6%, for sleeping disturbances 48.3% and 23.2% and for aberrant eating habits 60.3% and 14.3%, respectively.

CONCLUSION

An aberrant processing of sensory information appears to be a common feature in AS. The impact of these and other clinical features that are not incorporated in the ICD-10 and DSM-IV on our understanding of AS may hitherto have been underestimated. These associated clinical traits may well be reflected by the behavioural characteristics of these individuals.

From superior adaptation and function to brain dysfunction--the neglect of epigenetic factors

With optimal pregnancy conditions (natural, enriched diet which includes fish) African (Digo) infants are 3-4 weeks ahead of European/American infants in sensorimotor terms at birth, and during the first year. Infants of semi-aquatic sea-gypsies swim before they walk, and have superior visual acuity compared with us. With adverse pregnancy behaviour (fear of fat, a trend to dieting), neglecting the need for brain fat to secure normal brain development and function, we run a risk of dysfunction--death. Sudden Infant Death Syndrome victims have depressed birth weight, lower levels of marine fat in brainstem than controls, and >80 suffer multiple hypoxic episodes prior to death. Depressed birth weight (more than 10% below mean) is seen in learning and behaviour disorders, and a trend towards weights of less than 3kg is increasing, which supports a rise in antenatal sub optimality. Given marine fat deficiency in pregnancy and infancy, neurons starved for fuel could delay myelination and maturation in the latest developed Frontal Lobes. The phylogenetic oldest Lateral Frontal Lobe System (feed-back mechanism etc.) derived from olfactory bulb-amygdala, which crosses in Anterior Commisure is probably spared, while the Medial Frontal Lobe System derived from Hippocampus-Cingulum and crosses in Corpus Callosum (delayed response task) is most likely affected. The rise in infantile autism (intact vision and hearing) with deficit in delayed response task only, could suggest a deficit in the Medial Frontal Lobe System. The human species is unique; 70% of total energy to the foetus goes to development of the brain, which mainly consists of marine fat. It undergoes pervasive regressive events, before birth, in infancy and at puberty. Minimal retraction of neuronal arborisation is advantageous. Attributable to adverse pregnancy childrearing practice, excessive retraction is likely prenatally and in infancy. Pubertal age affects the fundamental property of nervous tissue, excitability: excessive excitatory drive is seen in early, and a deficiency in late puberty. It is postulated that with adequate marine fat, there is probably no risk of psychopathology at the extremes, whereas a deficiency could lead to paroxysmal (subcortical) dysfunction in early puberty, and breakdown of cortical circuitry and cognitive dysfunctions in late puberty. The post-pubertal psychoses, schizophrenia and manic-depressive psychosis at the extremes of the pubertal age continuum, with contrasting excitability and biological treatment, are probably the result of continuous dietary deficiency, which has inactivated the expression of genes for myelin development and oligodendrocyte-related genes in their production of myelin. The beneficial effect of marine fat in both disorders, in other CNS disorders as well as in developmental dyslexia (DD) and ADHD among others, supports our usual diet is persistently deficient. We have neglected the similarity of our great brain to other mammals, and our marine heritage. Given the amount of marine fat needed to secure normal brain development and function is not known, nor the present dietary level, it seems unduly conjectural to postulate that a dietary deficiency in marine fat is causing brain dysfunction and death. However, all observations point in the same direction: our diet focusing on protein mainly, is deficient, the deficiency is most pronounced in maternal nutrition and in infancy.

Auditory spatial localization and attention deficits in autistic adults

The objective of this study was to compare autistic adults and matched control subjects in their ability to focus attention selectively on a sound source in a noisy environment. Event-related brain potentials (ERPs) were recorded while subjects attended to a fast paced sequence of brief noise bursts presented in free-field at a central or peripheral location. Competing sequences of noise bursts at adjacent locations were to be ignored. Both behavioral measures of target detection and auditory ERP amplitudes indicated that control subjects were able to focus their attention more sharply on the relevant sound source than autistic subjects. These findings point to a fundamental deficit in the spatial focusing of auditory attention in autism, which may be a factor that impedes social interactions and sensory-guided behavior, particularly in noisy environments.

Long-term exposure to occupational noise alters the cortical organization of sound processing

OBJECTIVE

Long-term exposure to noise may cause an altered hemispheric lateralization of speech processing even in silent conditions. We examined whether this lateralization shift is speech specific or occurs also for other sounds.

METHODS

Brain responses from 10 healthy noise-exposed workers (>5 years) and 10 matched controls were recorded with a 32-channel electroencephalogram in two conditions, one including standard and deviant speech sounds, the other non-speech sounds, with novel sounds in both.

RESULTS

The deviant-sound elicited mismatch negativity (MMN) was larger to non-speech than speech sounds in control subjects, while it did not differ between the sound types in the noise-exposed subjects. Moreover, the MMN to speech sounds was lateralized to the right hemisphere in exposed workers, while it was left-hemisphere predominant in control subjects. No group topography difference was found for non-speech sounds. The deviant sounds that were close in formant space to the standards elicited a longer MMN latency in both speech and non-speech conditions in exposed subjects than controls. No group differences were found for cortical responses to novel sounds.

CONCLUSIONS

Long-term noise exposure altered the strength and the hemispheric organization of speech-sound discrimination and decreased the speed of sound-change processing.

SIGNIFICANCE

Subpathological changes in cortical responses to sounds may occur even in subjects without a peripheral damage but continuously exposed to noisy auditory environments.

Behavioral alterations in rats prenatally exposed to valproic acid: animal model of autism

Autism is a severe behavioral disorder characterized by pervasive impairments in social interactions, deficits in verbal and nonverbal communication, and stereotyped, repetitive patterns of behaviors and interests. Recently, a new rodent model of autism was created by exposure of rat fetuses to valproic acid (VPA) on the 12.5th day of gestation (VPA rats). The model has striking anatomical, pathological, and etiological similarities to human data; however, it has not been characterized behaviorally. In order to determine if VPA rats present behavioral aberrations observed in autism, their behavior was extensively evaluated in a battery of tests. The results of the present experiments demonstrate that VPA rats exhibit: (1) lower sensitivity to pain and higher sensitivity to nonpainful stimuli, (2) diminished acoustic prepulse inhibition, (3) locomotor and repetitive/stereotypic-like hyperactivity combined with lower exploratory activity, and (4) decreased number of social behaviors and increased latency to social behaviors. In addition, VPA rats showed delayed maturation, lower body weight, delayed motor development, and attenuated integration of a coordinated series of reflexes, delayed nest-seeking response mediated by olfactory system, and normal negative geotaxis. Interestingly, all behavioral aberrations described in this paper appear before puberty, which could distinguish the VPA rat model of autism from other animal models of neurodevelopmental disorders, especially rodent models of schizophrenia. Our results bring further support to validity of the proposed VPA animal model of autism, suggesting similarities between the observed pattern of behavioral alterations in VPA rats and features of disturbed behavior in autistic patients.

Deviant gaze processing in children with autism: an ERP study

This study investigated event-related potentials (ERP) during an oddball task in which detection of specific eye direction was required of children with and without autism. The detection of a change in eye direction elicited occipito-temporal negativity, which had two major differences between children with and without autism. First, while this occipito-temporal negativity predominated in the right hemisphere of typically developed children, it was distributed equally bilaterally in children with autism. Second, the amplitude of this negativity was more pronounced in typically developed children in response to the detection of direct gaze as compared to averted gaze, but was not sensitive to direct/averted gaze direction in children with autism, which converges with behavioral reports. The results concur with previous literature, suggesting the importance of the right hemisphere, especially the superior temporal sulcus, in gaze processing. Results indicate that deviant neural substrates might be involved in gaze processing in individuals with autism.

Abnormal cortical voice processing in autism

Impairments in social interaction are a key feature of autism and are associated with atypical social information processing. Here we report functional magnetic resonance imaging (fMRI) results showing that individuals with autism failed to activate superior temporal sulcus (STS) voice-selective regions in response to vocal sounds, whereas they showed a normal activation pattern in response to nonvocal sounds. These findings suggest abnormal cortical processing of socially relevant auditory information in autism.

Autism clinical trials: biological and medical issues in patient selection and treatment response

Biomedical measures are critical in the initial patient-screening and -selection phases of a clinical trial in autism and related disorders. These measures can also play an important role in the assessment and characterization of response and can provide an opportunity to study underlying etiologic and pathophysiologic processes. Thus, biomedical measures, including clinical laboratory analyses, metabolic screening, and chromosomal analysis, are used to screen for potential safety-related problems, to decrease biological and genetic heterogeneity, and to define subgroups. Neurobiological measures can be examined as possible predictors, modifiers or surrogates of therapeutic response, and adverse effects. Neurobiological research measures can also be used to study mechanisms and extent of drug action and to perform baseline and longitudinal investigations of possible pathophysiologic alterations. The potential utility and desirability of specific measures are considered and the general approach to choosing measures for incorporation is discussed.

Language and auditory processing in autism

Autism is characterized by varying degrees of disorders in language, communication and imagination. What are the prospects for making sense of this heterogeneous condition? Advances in identifying phenotypes in relation to subgroups within autism, based on disproportionate language impairment, have been recently reported by Tager-Flusberg and Joseph. The symptom severity of these subgroups requires investigation for underlying deficits, such as in auditory processing. Other recent reports support the view that a deficit in auditory processing might be a key factor in autism.