Overlapping but Divergent Neural Correlates Underpinning Audiovisual Synchrony and Temporal Order Judgments

Differences in audiovisual temporal processing in autistic adults are specific to simultaneity judgments

Research has shown that children on the autism spectrum and adults with high levels of autistic traits are less sensitive to audiovisual asynchrony compared to their neurotypical peers. However, this evidence has been limited to simultaneity judgments (SJ) which require participants to consider the timing of two cues together. Given evidence of partly divergent perceptual and neural mechanisms involved in making temporal order judgments (TOJ) and SJ, and given that SJ require a more global type of processing which may be impaired in autistic individuals, here we ask whether the observed differences in audiovisual temporal processing are task and stimulus specific. We examined the ability to detect audiovisual asynchrony in a group of 26 autistic adult males and a group of age and IQ-matched neurotypical males. Participants were presented with beep-flash, point-light drumming, and face-voice displays with varying degrees of asynchrony and asked to make SJ and TOJ. The results indicated that autistic participants were less able to detect audiovisual asynchrony compared to the control group, but this effect was specific to SJ and more complex social stimuli (e.g., face-voice) with stronger semantic correspondence between the cues, requiring a more global type of processing. This indicates that audiovisual temporal processing is not generally different in autistic individuals and that a similar level of performance could be achieved by using a more local type of processing, thus informing multisensory integration theory as well as multisensory training aimed to aid perceptual abilities in this population.

Past and present experience shifts audiovisual temporal perception in rats

Our brains have a propensity to integrate closely-timed auditory and visual stimuli into a unified percept; a phenomenon that is highly malleable based on prior sensory experiences, and is known to be altered in clinical populations. While the neural correlates of audiovisual temporal perception have been investigated using neuroimaging and electroencephalography techniques in humans, animal research will be required to uncover the underlying cellular and molecular mechanisms. Prior to conducting such mechanistic studies, it is important to first confirm the translational potential of any prospective animal model. Thus, in the present study, we conducted a series of experiments to determine if rats show the hallmarks of audiovisual temporal perception observed in neurotypical humans, and whether the rat behavioral paradigms could reveal when they experienced perceptual disruptions akin to those observed in neurodevelopmental disorders. After training rats to perform a temporal order judgment (TOJ) or synchrony judgment (SJ) task, we found that the rats' perception was malleable based on their past and present sensory experiences. More specifically, passive exposure to asynchronous audiovisual stimulation in the minutes prior to behavioral testing caused the rats' perception to predictably shift in the direction of the leading stimulus; findings which represent the first time that this form of audiovisual perceptual malleability has been reported in non-human subjects. Furthermore, rats performing the TOJ task also showed evidence of rapid recalibration, in which their audiovisual temporal perception on the current trial was predictably influenced by the timing lag between the auditory and visual stimuli in the preceding trial. Finally, by manipulating either experimental testing parameters or altering the rats' neurochemistry with a systemic injection of MK-801, we showed that the TOJ and SJ tasks could identify when the rats had difficulty judging the timing of audiovisual stimuli. These findings confirm that the behavioral paradigms are indeed suitable for future testing of rats with perceptual disruptions in audiovisual processing. Overall, our collective results highlight that rats represent an excellent animal model to study the cellular and molecular mechanisms underlying the acuity and malleability of audiovisual temporal perception, as they showcase the perceptual hallmarks commonly observed in humans.

Reduced audiovisual temporal sensitivity in Chinese children with dyslexia

Background

Temporal processing deficits regarding audiovisual cross-modal stimuli could affect children's speed and accuracy of decoding.

Aim

To investigate the characteristics of audiovisual temporal sensitivity (ATS) in Chinese children, with and without developmental dyslexia and its impact on reading ability.

Methods

The audiovisual simultaneity judgment and temporal order judgment tasks were performed to investigate the ATS of 106 Chinese children (53 with dyslexia) aged 8 to 12 and 37 adults without a history of dyslexia. The predictive effect of children's audiovisual time binding window on their reading ability and the effects of extra cognitive processing in the temporal order judgment task on participants' ATS were also investigated.

Outcomes and results

With increasing inter-stimulus intervals, the percentage of synchronous responses in adults declined more rapidly than in children. Adults and typically developing children had significantly narrower time binding windows than children with dyslexia. The size of visual stimuli preceding auditory stimuli time binding window had a marginally significant predictive effect on children's reading fluency. Compared with the simultaneity judgment task, the extra cognitive processing of the temporal order judgment task affected children's ATS.

Conclusion and implications

The ATS of 8-12-year-old Chinese children is immature. Chinese children with dyslexia have lower ATS than their peers.

Audiovisual temporal processing in adult patients with first-episode schizophrenia and high-functioning autism

Schizophrenia and autism spectrum disorder (ASD) are both neurodevelopmental disorders with altered sensory processing. Widened temporal binding window (TBW) signifies reduced sensitivity to detect stimulus asynchrony, and may be a shared feature in schizophrenia and ASD. Few studies directly compared audiovisual temporal processing ability in the two disorders. We recruited 43 adult patients with first-episode schizophrenia (FES), 35 average intelligent and verbally-fluent adult patients with high-functioning ASD and 48 controls. We employed two unisensory Temporal Order Judgement (TOJ) tasks within visual or auditory modalities, and two audiovisual Simultaneity Judgement (SJ) tasks with flash-beeps and videos of syllable utterance as stimuli. Participants with FES exhibited widened TBW affecting both speech and non-speech processing, which were not attributable to altered unisensory sensory acuity because they had normal visual and auditory TOJ thresholds. However, adults with ASD exhibited intact unisensory and audiovisual temporal processing. Lower non-verbal IQ was correlated with larger TBW width across the three groups. Taking our findings with earlier evidence in chronic samples, widened TBW is associated with schizophrenia regardless illness stage. The altered audiovisual temporal processing in ASD may ameliorate after reaching adulthood.

Unisensory and multisensory temporal processing in autism and dyslexia: A systematic review and meta-analysis

This study presents a comprehensive systematic review and meta-analysis of temporal processing in autism spectrum disorder (ASD) and developmental dyslexia (DD), two neurodevelopmental disorders in which temporal processing deficits have been highly researched. The results provide strong evidence for impairments in temporal processing in both ASD (g = 0.48) and DD (g = 0.82), as measured by judgments of temporal order and simultaneity. In individual analyses, multisensory temporal processing was impaired for both ASD and DD, and unisensory auditory, visual and tactile processing were all impaired in DD. In ASD, speech stimuli showed moderate impairment effect sizes, whereas nonspeech stimuli showed small effects. Greater reading and spelling skills in DD were associated with greater temporal precision. Temporal deficits did not show changes with age in either disorder. In addition to more clearly defining temporal impairments in ASD and DD, the results highlight common and distinct patterns of temporal processing between these disorders. Deficits are discussed in relation to existing theoretical models, and recommendations are made for future research.

Audiovisual temporal integration: Cognitive processing, neural mechanisms, developmental trajectory and potential interventions

To integrate auditory and visual signals into a unified percept, the paired stimuli must co-occur within a limited time window known as the Temporal Binding Window (TBW). The width of the TBW, a proxy of audiovisual temporal integration ability, has been found to be correlated with higher-order cognitive and social functions. A comprehensive review of studies investigating audiovisual TBW reveals several findings: (1) a wide range of top-down processes and bottom-up features can modulate the width of the TBW, facilitating adaptation to the changing and multisensory external environment; (2) a large-scale brain network works in coordination to ensure successful detection of audiovisual (a)synchrony; (3) developmentally, audiovisual TBW follows a U-shaped pattern across the lifespan, with a protracted developmental course into late adolescence and rebounding in size again in late life; (4) an enlarged TBW is characteristic of a number of neurodevelopmental disorders; and (5) the TBW is highly flexible via perceptual and musical training. Interventions targeting the TBW may be able to improve multisensory function and ameliorate social communicative symptoms in clinical populations.