Evidence for diminished multisensory integration in autism spectrum disorders

"Average is good, extremes are bad" - Non-linear inverted U-shaped relationship between neural mechanisms and functionality of mental features

Traditionally, studies emphasize differences in neural measures between pathological and healthy groups, assuming a binary distinction between the groups, and a linear relationship between neural measures and symptoms. Here, we present four examples that show a continuous relation across the divide of normal and pathological states between neural measures and mental functions. This relation can be characterized by a non-linear inverted-U shaped curve. Along this curve, mid-range or average expression of a neural measure is associated with optimal function of a mental feature (in healthy states), whereas extreme expression, either high or low, is associated with sub-optimal function, and occurs in different neural disorders. Neural expression between the optimal or intermediate and pathological or extreme values is associated with sub-optimal function and at-risk mental states. Thus, this model of neuro-mental relationship can be summarized as "average is good, extremes are bad". By focussing on neuro-mental relationships, this model can facilitate the transition of psychiatry from a categorical to a dimensional and individualized approach needed in the era of precision medicine.

Acquisition of Verb Meaning From Syntactic Distribution in Preschoolers With Autism Spectrum Disorder

Purpose

Our goal was to investigate whether preschool children with autism spectrum disorder (ASD) can begin to learn new word meanings by attending to the linguistic contexts in which they occur, even in the absence of visual or social context. We focused on verbs because of their importance for subsequent language development.

Method

Thirty-two children with ASD, ages 2;1-4;5 (years;months), participated in a verb-learning task. In a between-subjects design, they were randomly assigned to hear novel verbs in either transitive or intransitive syntactic frames while watching an unrelated silent animation or playing quietly with a toy. In an eye-tracking test, they viewed two video scenes, one depicting a causative event (e.g., boy spinning girl) and the other depicting synchronous events (e.g., boy and girl waving). They were prompted to find the referents of the novel verbs, and their eye gaze was measured.

Results

Like typically developing children in prior work, children with ASD who had heard the verbs in transitive syntactic frames preferred to look to the causative scene as compared to children who had heard intransitive frames.

Conclusions

This finding replicates and extends prior work on verb learning in children with ASD by demonstrating that they can attend to a novel verb's syntactic distribution absent relevant visual or social context, and they can use this information to assign the novel verb an appropriate meaning. We discuss points for future research, including examining individual differences that may impact success and contrasting social and nonsocial word-learning tasks directly.

Silent shapes and shapeless sounds: the robustness of the diminished crossmodal correspondences effect in autism spectrum conditions

We performed a registered replication of the Oberman and Ramachandran (Soc Neurosci 3(3–4):348–355, 2008) study on the ‘kiki/bouba’ effect in autism spectrum conditions (ASC). The aim of the study was to test the robustness of the diminished crossmodal correspondences effect in autism, but also to verify whether this effect is not an artifact of differences in intelligence. We tested a Polish-speaking sample of 21 participants with ADOS-confirmed autism spectrum conditions (mean age 15.90) and 21 age- (mean age 15.86), sex- and IQ-matched neurotypical control participants. Procedure closely followed the replicated study. Participants’ task was to match five pairs of unfamiliar words and shapes. Matching words and shapes had similar supramodal characteristics that allowed the match. We report partial replication of the diminished ‘kiki/bouba’ effect in individuals with ASC compared to the neurotypical control group. However, we found that nonverbal intelligence also significantly contributed to task performance, but only in participants with autism, suggesting a compensatory role of intelligence. Finally, the effect of autism severity (measured by ADOS classification) was significant—crossmodal correspondences were weaker in individuals with autism, compared to those with autism spectrum diagnosis.

Cross-situational and ostensive word learning in children with and without autism spectrum disorder

Numerous experimental studies have shown that infants and children can discover word meanings by using co-occurrences between labels and objects across individually ambiguous contexts-a phenomenon known as cross-situational learning. Like typically developing children, high-functioning school aged children with autism spectrum disorder (ASD) are capable of cross-situational learning. However, it is not yet clear whether cross-situational learning is similarly available to children with ASD who are younger and show a broader range of language and cognitive abilities. Using eye-tracking methodology, the current study provided the first evidence that preschool and early school-aged children with ASD can rely on cross-situational statistics to learn new words. In fact, children with ASD learned as well as typically developing children with similar vocabulary knowledge. In both groups, the children with the highest cross-situational learning accuracy were those who showed the best familiar word processing skills. Surprisingly, children in both groups learned words equally well in the cross-situational task and an ostensive word-learning task, which presented only a single label-object pairing at a time. In combination, these results point to similarities in the word learning abilities available to typically developing children and children with ASD.

Audiovisual multisensory integration in individuals with autism spectrum disorder: A systematic review and meta-analysis

An ever-growing literature has aimed to determine how individuals with autism spectrum disorder (ASD) differ from their typically developing (TD) peers on measures of multisensory integration (MSI) and to ascertain the degree to which differences in MSI are associated with the broad range of symptoms associated with ASD. Findings, however, have been highly variable across the studies carried out to date. The present work systematically reviews and quantitatively synthesizes the large literature on audiovisual MSI in individuals with ASD to evaluate the cumulative evidence for (a) group differences between individuals with ASD and TD peers, (b) correlations between MSI and autism symptoms in individuals with ASD and (c) study level factors that may moderate findings (i.e., explain differential effects) observed across studies. To identify eligible studies, a comprehensive search strategy was employed using the ProQuest search engine, PubMed database, forwards and backwards citation searches, direct author contact, and hand-searching of select conference proceedings. A significant between-group difference in MSI was evident in the literature, with individuals with ASD demonstrating worse audiovisual integration on average across studies compared to TD controls. This effect was moderated by mean participant age, such that between-group differences were more pronounced in younger samples. The mean correlation between MSI and autism and related symptomatology was also significant, indicating that increased audiovisual integration in individuals with ASD is associated with better language/communication abilities and/or reduced autism symptom severity in the extant literature. This effect was moderated by whether the stimuli were linguistic versus non-linguistic in nature, such that correlation magnitudes tended to be significantly greater when linguistic stimuli were utilized in the measure of MSI. Limitations and future directions for primary and meta-analytic research are discussed.

Does hearing aid use affect audiovisual integration in mild hearing impairment?

There is converging evidence for altered audiovisual integration abilities in hearing-impaired individuals and those with profound hearing loss who are provided with cochlear implants, compared to normal-hearing adults. Still, little is known on the effects of hearing aid use on audiovisual integration in mild hearing loss, although this constitutes one of the most prevalent conditions in the elderly and, yet, often remains untreated in its early stages. This study investigated differences in the strength of audiovisual integration between elderly hearing aid users and those with the same degree of mild hearing loss who were not using hearing aids, the non-users, by measuring their susceptibility to the sound-induced flash illusion. We also explored the corresponding window of integration by varying the stimulus onset asynchronies. To examine general group differences that are not attributable to specific hearing aid settings but rather reflect overall changes associated with habitual hearing aid use, the group of hearing aid users was tested unaided while individually controlling for audibility. We found greater audiovisual integration together with a wider window of integration in hearing aid users compared to their age-matched untreated peers. Signal detection analyses indicate that a change in perceptual sensitivity as well as in bias may underlie the observed effects. Our results and comparisons with other studies in normal-hearing older adults suggest that both mild hearing impairment and hearing aid use seem to affect audiovisual integration, possibly in the sense that hearing aid use may reverse the effects of hearing loss on audiovisual integration. We suggest that these findings may be particularly important for auditory rehabilitation and call for a longitudinal study.

Ripe for solution: Delayed development of multisensory processing in autism and its remediation

Difficulty integrating inputs from different sensory sources is commonly reported in individuals with Autism Spectrum Disorder (ASD). Accumulating evidence consistently points to altered patterns of behavioral reactions and neural activity when individuals with ASD observe or act upon information arriving through multiple sensory systems. For example, impairments in the integration of seen and heard speech appear to be particularly acute, with obvious implications for interpersonal communication. Here, we explore the literature on multisensory processing in autism with a focus on developmental trajectories. While much remains to be understood, some consistent observations emerge. Broadly, sensory integration deficits are found in children with an ASD whereas these appear to be much ameliorated, or even fully recovered, in older teenagers and adults on the spectrum. This protracted delay in the development of multisensory processing raises the possibility of applying early intervention strategies focused on multisensory integration, to accelerate resolution of these functions. We also consider how dysfunctional cross-sensory oscillatory neural communication may be one key pathway to impaired multisensory processing in ASD.

Distinct Autistic Traits Are Differentially Associated With the Width of the Multisensory Temporal Binding Window

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication and interaction, and restricted interests and behavior patterns. These characteristics are considered as a continuous distribution in the general population. People with ASD show atypical temporal processing in multisensory integration. Regarding the flash–beep illusion, which refers to how a single flash can be illusorily perceived as multiple flashes when multiple auditory beeps are concurrently presented, some studies reported that people with ASD have a wider temporal binding window and greater integration than typically developed people; others found the opposite or inconsistent tendencies. Here, we investigated the relationships between the manner of the flash–beep illusion and the various dimensions of ASD traits by estimating the degree of typically developed participants’ ASD traits including five subscales using the Autism-Spectrum Quotient. We found that stronger ASD traits of communication and social skill were associated with a wider and narrower temporal binding window respectively. These results suggest that specific ASD traits are differently involved in the particular temporal binding processes of audiovisual integration.

The impact of atypical sensory processing on social impairments in autism spectrum disorder

Altered sensory processing has been an important feature of the clinical descriptions of autism spectrum disorder (ASD). There is evidence that sensory dysregulation arises early in the progression of ASD and impacts social functioning. This paper reviews behavioral and neurobiological evidence that describes how sensory deficits across multiple modalities (vision, hearing, touch, olfaction, gustation, and multisensory integration) could impact social functions in ASD. Theoretical models of ASD and their implications for the relationship between sensory and social functioning are discussed. Furthermore, neural differences in anatomy, function, and connectivity of different regions underlying sensory and social processing are also discussed. We conclude that there are multiple mechanisms through which early sensory dysregulation in ASD could cascade into social deficits across development. Future research is needed to clarify these mechanisms, and specific focus should be given to distinguish between deficits in primary sensory processing and altered top-down attentional and cognitive processes.

An Investigation of the Relationships Between Autistic Traits and Crossmodal Correspondences in Typically Developing Adults

Autism spectrum disorder (ASD) includes characteristics such as social and behavioral deficits that are considered common across the general population rather than unique to people with the diagnosis. People with ASD are reported to have sensory irregularities, including crossmodal perception. Crossmodal correspondences are phenomena in which arbitrary crossmodal inputs affect behavioral performance. Crossmodal correspondences are considered to be established through associative learning, but the learning cues are considered to differ across the types of correspondences. In order to investigate whether and how ASD traits affect crossmodal associative learning, this study examined the relationships between the magnitude of crossmodal correspondences and the degree of ASD traits among non-diagnosed adults. We found that, among three types of crossmodal correspondences (brightness-loudness, visual size-pitch, and visual location-pitch pairs), the brightness-loudness pair was related with total ASD traits and a subtrait (social skill). The magnitude of newly learned crossmodal associations (the visual apparent motion direction-pitch pair) also showed a relationship with an ASD subtrait (attention switching). These findings demonstrate that there are unique relationships between crossmodal associations and ASD traits, indicating that each ASD trait is differently involved in sensory associative learning.

Increases in the autistic trait of attention to detail are associated with decreased multisensory temporal adaptation

Recent empirical evidence suggests that autistic individuals perceive the world differently than their typically-developed peers. One theoretical account, the predictive coding hypothesis, posits that autistic individuals show a decreased reliance on previous perceptual experiences, which may relate to autism symptomatology. We tested this through a well-characterized, audiovisual statistical-learning paradigm in which typically-developed participants were first adapted to consistent temporal relationships between audiovisual stimulus pairs (audio-leading, synchronous, visual-leading) and then performed a simultaneity judgement task with audiovisual stimulus pairs varying in temporal offset from auditory-leading to visual-leading. Following exposure to the visual-leading adaptation phase, participants' perception of synchrony was biased towards visual-leading presentations, reflecting the statistical regularities of their previously experienced environment. Importantly, the strength of adaptation was significantly related to the level of autistic traits that the participant exhibited, measured by the Autism Quotient (AQ). This was specific to the Attention to Detail subscale of the AQ that assesses the perceptual propensity to focus on fine-grain aspects of sensory input at the expense of more integrative perceptions. More severe Attention to Detail was related to weaker adaptation. These results support the predictive coding framework, and suggest that changes in sensory perception commonly reported in autism may contribute to autistic symptomatology.

Brief Report: Which Came First? Exploring Crossmodal Temporal Order Judgements and Their Relationship with Sensory Reactivity in Autism and Neurotypicals

Previous studies have indicated that visual-auditory temporal acuity is reduced in children with autism spectrum conditions (ASC) in comparison to neurotypicals. In the present study we investigated temporal acuity for all possible bimodal pairings of visual, tactile and auditory information in adults with ASC (n = 18) and a matched control group (n = 18). No group differences in temporal acuity for crossmodal stimuli were observed, suggesting that this may be typical in adults with ASC. However, visual-tactile temporal acuity and bias towards vision when presented with visual-auditory information were both predictors of self-reported sensory reactivity. This suggests that reduced multisensory temporal acuity and/or attention towards vision may contribute to atypical sensory reactivity.

A Predictive Coding Account of Psychotic Symptoms in Autism Spectrum Disorder

The co-occurrence of psychotic and autism spectrum disorder (ASD) symptoms represents an important clinical challenge. Here we consider this problem in the context of a computational psychiatry approach that has been applied to both conditions-predictive coding. Some symptoms of schizophrenia have been explained in terms of a failure of top-down predictions or an enhanced weighting of bottom-up prediction errors. Likewise, autism has been explained in terms of similar perturbations. We suggest that this theoretical overlap may explain overlapping symptomatology. Experimental evidence highlights meaningful distinctions and consistencies between these disorders. We hypothesize individuals with ASD may experience some degree of delusions without the presence of any additional impairment, but that hallucinations are likely indicative of a distinct process.

Sensory perception in autism

Autism is a complex neurodevelopmental condition, and little is known about its neurobiology. Much of autism research has focused on the social, communication and cognitive difficulties associated with the condition. However, the recent revision of the diagnostic criteria for autism has brought another key domain of autistic experience into focus: sensory processing. Here, we review the properties of sensory processing in autism and discuss recent computational and neurobiological insights arising from attention to these behaviours. We argue that sensory traits have important implications for the development of animal and computational models of the condition. Finally, we consider how difficulties in sensory processing may relate to the other domains of behaviour that characterize autism.

Multisensory speech perception in autism spectrum disorder: From phoneme to whole-word perception

Speech perception in noisy environments is boosted when a listener can see the speaker's mouth and integrate the auditory and visual speech information. Autistic children have a diminished capacity to integrate sensory information across modalities, which contributes to core symptoms of autism, such as impairments in social communication. We investigated the abilities of autistic and typically-developing (TD) children to integrate auditory and visual speech stimuli in various signal-to-noise ratios (SNR). Measurements of both whole-word and phoneme recognition were recorded. At the level of whole-word recognition, autistic children exhibited reduced performance in both the auditory and audiovisual modalities. Importantly, autistic children showed reduced behavioral benefit from multisensory integration with whole-word recognition, specifically at low SNRs. At the level of phoneme recognition, autistic children exhibited reduced performance relative to their TD peers in auditory, visual, and audiovisual modalities. However, and in contrast to their performance at the level of whole-word recognition, both autistic and TD children showed benefits from multisensory integration for phoneme recognition. In accordance with the principle of inverse effectiveness, both groups exhibited greater benefit at low SNRs relative to high SNRs. Thus, while autistic children showed typical multisensory benefits during phoneme recognition, these benefits did not translate to typical multisensory benefit of whole-word recognition in noisy environments. We hypothesize that sensory impairments in autistic children raise the SNR threshold needed to extract meaningful information from a given sensory input, resulting in subsequent failure to exhibit behavioral benefits from additional sensory information at the level of whole-word recognition. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1280-1290. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Magnetoencephalographic Imaging of Auditory and Somatosensory Cortical Responses in Children with Autism and Sensory Processing Dysfunction

This study compared magnetoencephalographic (MEG) imaging-derived indices of auditory and somatosensory cortical processing in children aged 8–12 years with autism spectrum disorder (ASD; N = 18), those with sensory processing dysfunction (SPD; N = 13) who do not meet ASD criteria, and typically developing control (TDC; N = 19) participants. The magnitude of responses to both auditory and tactile stimulation was comparable across all three groups; however, the M200 latency response from the left auditory cortex was significantly delayed in the ASD group relative to both the TDC and SPD groups, whereas the somatosensory response of the ASD group was only delayed relative to TDC participants. The SPD group did not significantly differ from either group in terms of somatosensory latency, suggesting that participants with SPD may have an intermediate phenotype between ASD and TDC with regard to somatosensory processing. For the ASD group, correlation analyses indicated that the left M200 latency delay was significantly associated with performance on the WISC-IV Verbal Comprehension Index as well as the DSTP Acoustic-Linguistic index. Further, these cortical auditory response delays were not associated with somatosensory cortical response delays or cognitive processing speed in the ASD group, suggesting that auditory delays in ASD are domain specific rather than associated with generalized processing delays. The specificity of these auditory delays to the ASD group, in addition to their correlation with verbal abilities, suggests that auditory sensory dysfunction may be implicated in communication symptoms in ASD, motivating further research aimed at understanding the impact of sensory dysfunction on the developing brain.

The cascading influence of multisensory processing on speech perception in autism

It has been recently theorized that atypical sensory processing in autism relates to difficulties in social communication. Through a series of tasks concurrently assessing multisensory temporal processes, multisensory integration and speech perception in 76 children with and without autism, we provide the first behavioral evidence of such a link. Temporal processing abilities in children with autism contributed to impairments in speech perception. This relationship was significantly mediated by their abilities to integrate social information across auditory and visual modalities. These data describe the cascading impact of sensory abilities in autism, whereby temporal processing impacts multisensory information of social information, which, in turn, contributes to deficits in speech perception. These relationships were found to be specific to autism, specific to multisensory but not unisensory integration, and specific to the processing of social information.

A Predictive Coding Account of Psychotic Symptoms in Autism Spectrum Disorder

The co-occurrence of psychotic and autism spectrum disorder (ASD) symptoms represents an important clinical challenge. Here we consider this problem in the context of a computational psychiatry approach that has been applied to both conditions-predictive coding. Some symptoms of schizophrenia have been explained in terms of a failure of top-down predictions or an enhanced weighting of bottom-up prediction errors. Likewise, autism has been explained in terms of similar perturbations. We suggest that this theoretical overlap may explain overlapping symptomatology. Experimental evidence highlights meaningful distinctions and consistencies between these disorders. We hypothesize individuals with ASD may experience some degree of delusions without the presence of any additional impairment, but that hallucinations are likely indicative of a distinct process.

Links between temporal acuity and multisensory integration across life span

The temporal relationship between individual pieces of information from the different sensory modalities is one of the stronger cues to integrate such information into a unified perceptual gestalt, conveying numerous perceptual and behavioral advantages. Temporal acuity, however, varies greatly over the life span. It has previously been hypothesized that changes in temporal acuity in both development and healthy aging may thus play a key role in integrative abilities. This study tested the temporal acuity of 138 individuals ranging in age from 5 to 80. Temporal acuity and multisensory integration abilities were tested both within and across modalities (audition and vision) with simultaneity judgment and temporal order judgment tasks. We observed that temporal acuity, both within and across modalities, improved throughout development into adulthood and subsequently declined with healthy aging, as did the ability to integrate multisensory speech information. Of importance, throughout development, temporal acuity of simple stimuli (i.e., flashes and beeps) predicted individuals' abilities to integrate more complex speech information. However, in the aging population, although temporal acuity declined with healthy aging and was accompanied by declines in integrative abilities, temporal acuity was not able to predict integration at the individual level. Together, these results suggest that the impact of temporal acuity on multisensory integration varies throughout the life span. Although the maturation of temporal acuity drives the rise of multisensory integrative abilities during development, it is unable to account for changes in integrative abilities in healthy aging. The differential relationships between age, temporal acuity, and multisensory integration suggest an important role for experience in these processes. (PsycINFO Database Record

A simple and efficient method to enhance audiovisual binding tendencies

Individuals vary in their tendency to bind signals from multiple senses. For the same set of sights and sounds, one individual may frequently integrate multisensory signals and experience a unified percept, whereas another individual may rarely bind them and often experience two distinct sensations. Thus, while this binding/integration tendency is specific to each individual, it is not clear how plastic this tendency is in adulthood, and how sensory experiences may cause it to change. Here, we conducted an exploratory investigation which provides evidence that (1) the brain’s tendency to bind in spatial perception is plastic, (2) that it can change following brief exposure to simple audiovisual stimuli, and (3) that exposure to temporally synchronous, spatially discrepant stimuli provides the most effective method to modify it. These results can inform current theories about how the brain updates its internal model of the surrounding sensory world, as well as future investigations seeking to increase integration tendencies.

An autism-associated serotonin transporter variant disrupts multisensory processing

Altered sensory processing is observed in many children with autism spectrum disorder (ASD), with growing evidence that these impairments extend to the integration of information across the different senses (that is, multisensory function). The serotonin system has an important role in sensory development and function, and alterations of serotonergic signaling have been suggested to have a role in ASD. A gain-of-function coding variant in the serotonin transporter (SERT) associates with sensory aversion in humans, and when expressed in mice produces traits associated with ASD, including disruptions in social and communicative function and repetitive behaviors. The current study set out to test whether these mice also exhibit changes in multisensory function when compared with wild-type (WT) animals on the same genetic background. Mice were trained to respond to auditory and visual stimuli independently before being tested under visual, auditory and paired audiovisual (multisensory) conditions. WT mice exhibited significant gains in response accuracy under audiovisual conditions. In contrast, although the SERT mutant animals learned the auditory and visual tasks comparably to WT littermates, they failed to show behavioral gains under multisensory conditions. We believe these results provide the first behavioral evidence of multisensory deficits in a genetic mouse model related to ASD and implicate the serotonin system in multisensory processing and in the multisensory changes seen in ASD.

Similarities in Autistic and Neurotypical Visual–Haptic Perception When Making Judgements About Conflicting Sensory Stimuli

A number of studies have shown that multisensory performance is well predicted by a statistically optimal maximum likelihood estimation (MLE) model. Under this model unisensory estimates are combined additively and weighted according to relative reliability. Recent theories have proposed that atypical sensation and perception commonly reported in autism spectrum condition (ASC) may result from differences in the use of reliability information. Furthermore, experimental studies have indicated that multisensory processing is less effective in those with the condition in comparison to neurotypical (NT) controls. In the present study, adults with ASC () and a matched NT group () completed a visual–haptic size judgement task (cf. Gori et al., 2008) in which participants compared the height of wooden blocks using either vision or haptics, and in a dual modality condition in which visual–haptic stimuli were presented in size conflict. Participants with ASC tended to produce more reliable estimates than the NT group. However, dual modality performance was not well predicted by the MLE model for either group. Performance was subsequently compared to alternative models in which the participant either switched between modalities trial to trial (rather than integrating) and a model of non-optimal integration. Performance of both groups was statistically comparable to the cue-switching model. These findings suggest that adults with ASC adopted a similar strategy to NTs when processing conflicting visual–haptic information. Findings are discussed in relation to multisensory perception in ASC and methodological considerations associated with multisensory conflict paradigms.

Effects of multisensory integration processes on response inhibition in adolescent autism spectrum disorder

BACKGROUND

In everyday life it is often required to integrate multisensory input to successfully conduct response inhibition (RI) and thus major executive control processes. Both RI and multisensory processes have been suggested to be altered in autism spectrum disorder (ASD). It is, however, unclear which neurophysiological processes relate to changes in RI in ASD and in how far these processes are affected by possible multisensory integration deficits in ASD.

METHOD

Combining high-density EEG recordings with source localization analyses, we examined a group of adolescent ASD patients (n = 20) and healthy controls (n = 20) using a novel RI task.

RESULTS

Compared to controls, RI processes are generally compromised in adolescent ASD. This aggravation of RI processes is modulated by the content of multisensory information. The neurophysiological data suggest that deficits in ASD emerge in attentional selection and resource allocation processes related to occipito-parietal and middle frontal regions. Most importantly, conflict monitoring subprocesses during RI were specifically modulated by content of multisensory information in the superior frontal gyrus.

CONCLUSIONS

RI processes are overstrained in adolescent ASD, especially when conflicting multisensory information has to be integrated to perform RI. It seems that the content of multisensory input is important to consider in ASD and its effects on cognitive control processes.

The Role of Sensorimotor Difficulties in Autism Spectrum Conditions

In addition to difficulties in social communication, current diagnostic criteria for autism spectrum conditions (ASC) also incorporate sensorimotor difficulties, repetitive motor movements, and atypical reactivity to sensory input (1). This paper explores whether sensorimotor difficulties are associated with the development and maintenance of symptoms in ASC. First, studies have shown difficulties coordinating sensory input into planning and executing movement effectively in ASC. Second, studies have shown associations between sensory reactivity and motor coordination with core ASC symptoms, suggesting these areas each strongly influence the development of social and communication skills. Third, studies have begun to demonstrate that sensorimotor difficulties in ASC could account for reduced social attention early in development, with a cascading effect on later social, communicative and emotional development. These results suggest that sensorimotor difficulties not only contribute to non-social difficulties such as narrow circumscribed interests, but also to the development of social behaviors such as effectively coordinating eye contact with speech and gesture, interpreting others' behavior, and responding appropriately. Further research is needed to explore the link between sensory and motor difficulties in ASC and their contribution to the development and maintenance of ASC.

Intramodal Olfactory Priming of Positive and Negative Odors in Humans Using Respiration-Triggered Olfactory Stimulation (RETROS)

Priming describes the principle of modified stimulus perception that occurs due to a previously presented stimulus. Although we have begun to understand the mechanisms of crossmodal priming, the concept of intramodal olfactory priming remains relatively unexplored. Therefore, we applied positive and negative odors using respiration-triggered olfactory stimulation (RETROS), enabling us to record the skin conductance response (SCR) and breathing data without a crossmodal cueing error and measure reaction times (RTs) for olfactory tasks. RT, SCR, and breathing data revealed that negative odors were perceived significantly more arousing than positive ones. In a second experiment, 2 odors were applied during consecutive respirations. Here, we observed intramodal olfactory priming effects: A negative odor preceded by a positive odor was rated as more pleasant than when the same odor was preceded by a negative odor. Additionally, a longer identification RT was found for the second compared with the first odor. We interpret this as increased "perceptual load" due to incomplete first odor processing while the second odor was presented. Furthermore, intramodal priming can be considered a possible reason for the increase of identification RT. The use of RETROS led to these novel insights into olfactory processing beyond crossmodal interaction by providing a noncued unimodal olfactory test, and therefore, RETROS can be used in the experimental design of future olfactory studies.

Investigating visual-tactile interactions over time and space in adults with autism

It has been suggested that the sensory symptoms which affect many people with autism spectrum conditions (ASC) may be related to alterations in multisensory processing. Typically, the likelihood of interactions between the senses increases when information is temporally and spatially coincident. We explored visual-tactile interactions in adults with ASC for the first time in two experiments using low-level stimuli. Both participants with ASC and matched neurotypical controls only produced crossmodal interactions to near simultaneous stimuli, suggesting that temporal modulation is unaffected in the adult population. We also provide preliminary evidence that visual-tactile interactions may occur over greater spatial distances in participants with ASC, which merits further exploration.

The Disrupted Connectivity Hypothesis of Autism Spectrum Disorders: Time for the Next Phase in Research

During the past decade, the disrupted connectivity theory has generated considerable interest as a pathophysiological model for autism spectrum disorders (ASD). This theory postulates that deficiencies in the way the brain coordinates and synchronizes activity amongst different regions may account for the clinical symptoms of ASD. This review critically examines the current structural and functional connectivity data in ASD and evaluates unresolved assumptions and gaps in knowledge that limit the interpretation of these data. Collectively, studies very often show group alterations in what are thought of as measures of cerebral connectivity, though the patterns of findings vary considerably. We argue that there are three principle needs in this research agenda. First, further basic research is needed to understand the links between measures commonly used (DTI, fMRI, EEG) and other (histological, computational) levels of analysis. Second, speculated causes of inconsistencies in the literature (age, clinical heterogeneity) demand studies that directly evaluate these interpretations. Finally, the field needs well-specified mechanistic models of altered cerebral communication in ASD whose predictions can be tested on multiple levels of analyses.

The Brain's Tendency to Bind Audiovisual Signals Is Stable but Not General

Previous studies have shown a surprising amount of between-subjects variability in the strength of interactions between sensory modalities. For the same set of stimuli, some subjects exhibit strong interactions, whereas others exhibit weak interactions. To date, little is known about what underlies this variability. Sensory integration in the brain could be governed by a global mechanism or by task-specific mechanisms that could be either stable or variable across time. We used a rigorous quantitative tool (Bayesian causal inference) to investigate whether integration (i.e., binding) tendencies generalize across tasks and are stable across time. We report for the first time that individuals' binding tendencies are stable across time but are task-specific. These results provide evidence against the hypothesis that sensory integration is governed by a single, global parameter in the brain.

Stimulus intensity modulates multisensory temporal processing

One of the more challenging feats that multisensory systems must perform is to determine which sensory signals originate from the same external event, and thus should be integrated or "bound" into a singular perceptual object or event, and which signals should be segregated. Two important stimulus properties impacting this process are the timing and effectiveness of the paired stimuli. It has been well established that the more temporally aligned two stimuli are, the greater the degree to which they influence one another's processing. In addition, the less effective the individual unisensory stimuli are in eliciting a response, the greater the benefit when they are combined. However, the interaction between stimulus timing and stimulus effectiveness in driving multisensory-mediated behaviors has never been explored - which was the purpose of the current study. Participants were presented with either high- or low-intensity audiovisual stimuli in which stimulus onset asynchronies (SOAs) were parametrically varied, and were asked to report on the perceived synchrony/asynchrony of the paired stimuli. Our results revealed an interaction between the temporal relationship (SOA) and intensity of the stimuli. Specifically, individuals were more tolerant of larger temporal offsets (i.e., more likely to call them synchronous) when the paired stimuli were less effective. This interaction was also seen in response time (RT) distributions. Behavioral gains in RTs were seen with synchronous relative to asynchronous presentations, but this effect was more pronounced with high-intensity stimuli. These data suggest that stimulus effectiveness plays an underappreciated role in the perception of the timing of multisensory events, and reinforces the interdependency of the principles of multisensory integration in determining behavior and shaping perception.

Behavioral, perceptual, and neural alterations in sensory and multisensory function in autism spectrum disorder

Although sensory processing challenges have been noted since the first clinical descriptions of autism, it has taken until the release of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) in 2013 for sensory problems to be included as part of the core symptoms of autism spectrum disorder (ASD) in the diagnostic profile. Because sensory information forms the building blocks for higher-order social and cognitive functions, we argue that sensory processing is not only an additional piece of the puzzle, but rather a critical cornerstone for characterizing and understanding ASD. In this review we discuss what is currently known about sensory processing in ASD, how sensory function fits within contemporary models of ASD, and what is understood about the differences in the underlying neural processing of sensory and social communication observed between individuals with and without ASD. In addition to highlighting the sensory features associated with ASD, we also emphasize the importance of multisensory processing in building perceptual and cognitive representations, and how deficits in multisensory integration may also be a core characteristic of ASD.

Keeping time in the brain: Autism spectrum disorder and audiovisual temporal processing

A growing area of interest and relevance in the study of autism spectrum disorder (ASD) focuses on the relationship between multisensory temporal function and the behavioral, perceptual, and cognitive impairments observed in ASD. Atypical sensory processing is becoming increasingly recognized as a core component of autism, with evidence of atypical processing across a number of sensory modalities. These deviations from typical processing underscore the value of interpreting ASD within a multisensory framework. Furthermore, converging evidence illustrates that these differences in audiovisual processing may be specifically related to temporal processing. This review seeks to bridge the connection between temporal processing and audiovisual perception, and to elaborate on emerging data showing differences in audiovisual temporal function in autism. We also discuss the consequence of such changes, the specific impact on the processing of different classes of audiovisual stimuli (e.g. speech vs. nonspeech, etc.), and the presumptive brain processes and networks underlying audiovisual temporal integration. Finally, possible downstream behavioral implications, and possible remediation strategies are outlined. Autism Res 2016, 9: 720-738. © 2015 International Society for Autism Research, Wiley Periodicals, Inc.

Self-motion perception in autism is compromised by visual noise but integrated optimally across multiple senses

Perceptual processing in autism spectrum disorder (ASD) is marked by superior low-level task performance and inferior complex-task performance. This observation has led to theories of defective integration in ASD of local parts into a global percept. Despite mixed experimental results, this notion maintains widespread influence and has also motivated recent theories of defective multisensory integration in ASD. Impaired ASD performance in tasks involving classic random dot visual motion stimuli, corrupted by noise as a means to manipulate task difficulty, is frequently interpreted to support this notion of global integration deficits. By manipulating task difficulty independently of visual stimulus noise, here we test the hypothesis that heightened sensitivity to noise, rather than integration deficits, may characterize ASD. We found that although perception of visual motion through a cloud of dots was unimpaired without noise, the addition of stimulus noise significantly affected adolescents with ASD, more than controls. Strikingly, individuals with ASD demonstrated intact multisensory (visual-vestibular) integration, even in the presence of noise. Additionally, when vestibular motion was paired with pure visual noise, individuals with ASD demonstrated a different strategy than controls, marked by reduced flexibility. This result could be simulated by using attenuated (less reliable) and inflexible (not experience-dependent) Bayesian priors in ASD. These findings question widespread theories of impaired global and multisensory integration in ASD. Rather, they implicate increased sensitivity to sensory noise and less use of prior knowledge in ASD, suggesting increased reliance on incoming sensory information.

Testing sensory and multisensory function in children with autism spectrum disorder

In addition to impairments in social communication and the presence of restricted interests and repetitive behaviors, deficits in sensory processing are now recognized as a core symptom in autism spectrum disorder (ASD). Our ability to perceive and interact with the external world is rooted in sensory processing. For example, listening to a conversation entails processing the auditory cues coming from the speaker (speech content, prosody, syntax) as well as the associated visual information (facial expressions, gestures). Collectively, the "integration" of these multisensory (i.e., combined audiovisual) pieces of information results in better comprehension. Such multisensory integration has been shown to be strongly dependent upon the temporal relationship of the paired stimuli. Thus, stimuli that occur in close temporal proximity are highly likely to result in behavioral and perceptual benefits--gains believed to be reflective of the perceptual system's judgment of the likelihood that these two stimuli came from the same source. Changes in this temporal integration are expected to strongly alter perceptual processes, and are likely to diminish the ability to accurately perceive and interact with our world. Here, a battery of tasks designed to characterize various aspects of sensory and multisensory temporal processing in children with ASD is described. In addition to its utility in autism, this battery has great potential for characterizing changes in sensory function in other clinical populations, as well as being used to examine changes in these processes across the lifespan.

A novel behavioral paradigm to assess multisensory processing in mice

Human psychophysical and animal behavioral studies have illustrated the benefits that can be conferred from having information available from multiple senses. Given the central role of multisensory integration for perceptual and cognitive function, it is important to design behavioral paradigms for animal models to provide mechanistic insights into the neural bases of these multisensory processes. Prior studies have focused on large mammals, yet the mouse offers a host of advantages, most importantly the wealth of available genetic manipulations relevant to human disease. To begin to employ this model species for multisensory research it is necessary to first establish and validate a robust behavioral assay for the mouse. Two common mouse strains (C57BL/6J and 129S6/SvEv) were first trained to respond to unisensory (visual and auditory) stimuli separately. Once trained, performance with paired audiovisual stimuli was then examined with a focus on response accuracy and behavioral gain. Stimulus durations varied from 50 ms to 1 s in order to modulate the effectiveness of the stimuli and to determine if the well-established "principle of inverse effectiveness" held in this model. Response accuracy in the multisensory condition was greater than for either unisensory condition for all stimulus durations, with significant gains observed at the 300 ms and 100 ms durations. Main effects of stimulus duration, stimulus modality and a significant interaction between these factors were observed. The greatest behavioral gain was seen for the 100 ms duration condition, with a trend observed that as the stimuli became less effective, larger behavioral gains were observed upon their pairing (i.e., inverse effectiveness). These results are the first to validate the mouse as a species that shows demonstrable behavioral facilitations under multisensory conditions and provides a platform for future mechanistically directed studies to examine the neural bases of multisensory integration.