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People with autism spectrum disorder (ASD) or higher levels of autistic traits have atypical characteristics in sensory processing. Atypicalities have been reported for proprioceptive judgments, which are tightly related to internal bodily representations underlying position sense. However, no research has directly investigated whether self-bodily representations are different in individuals with ASD. Implicit hand maps, estimated based on participants' proprioceptive sensations without sight of their hand, are known to be distorted such that the shape is stretched along the medio-lateral hand axis even for neurotypical participants. Here, with the view of ASD as falling on a continuous distribution among the general population, we explored differences in implicit body representations along with autistic traits by focusing on relationships between autistic traits and the magnitudes of the distortions in implicit hand maps (N ~ 100). We estimated the magnitudes of distortions in implicit hand maps both for fingers and hand surfaces on the dorsal and palmar sides of the hand. Autistic traits were measured by questionnaires (Autism Spectrum [AQ] and Empathy/Systemizing [EQ-SQ] Quotients). The distortions in implicit hand maps were replicated in our experimental situations. However, there were no significant relationships between autistic traits and the magnitudes of the distortions as well as within-individual variabilities in the maps and localization performances. Consistent results were observed from comparisons between IQ-matched samples of people with and without a diagnosis of ASD. Our findings suggest that there exist perceptual and neural processes for implicit body representations underlying position sense consistent across levels of autistic traits., (© 2023 International Society for Autism Research, Wiley Periodicals LLC.)

Non-synesthetes exhibit a tendency to associate specific shapes with particular colors (i.e., circle-red, triangle-yellow, and square-blue). Such color-shape associations (CSAs) could potentially affect the feature binding of colors and shapes, thus resulting in people reporting more binding errors in the case of incongruent, rather than congruent, colored-shape pairs. Individuals with autism spectrum disorder (ASD) exhibit atypical sensory processing and impaired multisensory integration. Here, we examined whether autistic traits (Autism-Spectrum Quotient; AQ) influence the strength of color-shape associations, as evidenced by the occurrence of binding errors in incongruent minus congruent conditions. Participants took part in an experiment designed to reveal binding errors induced by incongruent and congruent colored-shape pairs, and completed the Japanese version of the AQ score. The results revealed a significant correlation between AQ scores and occurrence of binding errors when participants were presented with the circle-red and triangle-yellow CSAs: That is, individuals with higher autistic traits tend to make more binding errors in incongruent minus congruent colored-shape pairs, indicating a stronger binding of circle-red and triangle-yellow associations. These results therefore suggest that autistic traits play a role in forming color-shape associations, shedding light on the nature of both color-shape associations and autistic perception., (© 2023. The Author(s).)

The number of clinical diagnoses of autism spectrum disorder (ASD) is increasing annually. Interestingly, the human body temperature has also been reported to gradually decrease over the decades. An imbalance in the activation of the excitatory and inhibitory neurons is assumed to be involved in the pathogenesis of ASD. Neurophysiological evidence showed that brain activity decreases as cortical temperature increases, suggesting that an increase in brain temperature enhances the inhibitory neural mechanisms. Behavioral characteristics specific to clinical ASD were observed to be moderated when people with the diagnoses had a fever. To explore the possible relationship between ASD and body temperature in the general population, we conducted a survey study using a large population-based sample (N ~ 2000, in the age groups 20s to 70s). Through two surveys, multiple regression analyses did not show significant relationships between axillary temperatures and autistic traits measured by questionnaires (Autism Spectrum (AQ) and Empathy/Systemizing Quotients), controlling for covariates of age and self-reported circadian rhythms. Conversely, we consistently observed a negative relationship between AQ and age. People with higher AQ scores tended to have stronger eveningness. Our findings contribute to the understanding of age-related malleability and the irregularity of circadian rhythms related to autistic traits., (© 2023. The Author(s).)

Previous psychophysical studies reported a positive aftereffect in tactile temporal order judgments, which can be explained by the Bayesian estimation model ('Bayesian calibration'). We investigated the relationship between Bayesian calibration and autistic traits in participants with typical development (TD) and autism spectrum disorder (ASD). Bayesian calibration was weakened in TD participants with high autistic traits, consistent with the 'hypo-priors' hypothesis for autistic perceptions. The results from the ASD group were generally observed as a continuation of those from the TD groups. Meanwhile, two ASD participants showed irregularly large positive or negative aftereffects. We discussed the mechanisms behind the general results among TD and ASD participants and two particular results among ASD participants based on the Bayesian estimation model., (© 2022. The Author(s).)

Individuals with autism spectrum disorder exhibit atypical taste perception and eating behaviours. However, little is known about the effect of autistic traits on eating behaviours in the general population. This study explored the relationships between autistic traits, taste preferences, taste perceptions, and eating behaviours among Japanese population using an online questionnaire survey. The results showed significant effect of autistic traits on eating behaviours, that people with higher autistic traits tended to have higher selective eating behaviours, such as increased sensitivity to food texture and mixed flavours. Moreover, selective eating behaviours were correlated with the preference for sour taste and aftertaste sensitivity. Those results suggest that eating behaviours can be influenced by the relationship between autistic traits, taste perceptions, and taste preferences. We discuss these results in the context of previous findings, and future investigations into the possibility of solving selective eating problems in individuals with autism., (© 2022 The Authors. European Eating Disorders Review published by Eating Disorders Association and John Wiley & Sons Ltd.)

Individuals with autism spectrum disorder (ASD) have atypical sensory processing, particularly when sensory stimuli are delivered from different modalities with a temporal lag of subseconds. Previous studies have suggested that individuals with ASD require a longer temporal lag to judge temporal orders of successive audiovisual stimuli than neurotypical individuals; however, it remains unclear whether a lower temporal resolution in the visuotactile domain is associated with an individual's autistic traits. In addition, a previous study demonstrated that visuotactile temporal resolution degraded when the participants saw a hand image on a display. In this study, we investigated whether the temporal resolution of the visuotactile stimuli degrades when the participant's own hand or rubber hands are visible, and whether the effect of the hand's visibility on the temporal resolution decreases according to an individual's autistic traits. We used the temporal order judgment (TOJ) of the vibrotactile stimulus delivered to the participant's index finger and an LED attached above their own hand or rubber hand. Our findings suggest that when participants could not see their hand, temporal order judgment tended to be coarser in participants with higher autistic traits. However, this tendency was not observed when they could see both their own or the rubber hands. Moreover, temporal resolution degraded when the participants could see their own hands. These results indicate that autistic traits influence the temporal resolution of visuotactile stimuli if they are delivered as external signals in TOJ., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Eye movements toward sequentially presented face images with or without gaze cues were recorded to investigate whether those with ASD, in comparison to their typically developing (TD) peers, could prospectively perform the task according to gaze cues. Line-drawn face images were sequentially presented for one second each on a laptop PC display, and the face images shifted from side-to-side and up-and-down. In the gaze cue condition, the gaze of the face image was directed to the position where the next face would be presented. Although the participants with ASD looked less at the eye area of the face image than their TD peers, they could perform comparable smooth gaze shift to the gaze cue of the face image in the gaze cue condition. This appropriate gaze shift in the ASD group was more evident in the second half of trials in than in the first half, as revealed by the mean proportion of fixation time in the eye area to valid gaze data in the early phase (during face image presentation) and the time to first fixation on the eye area. These results suggest that individuals with ASD may benefit from the short-period trial experiment by enhancing the usage of gaze cue.

Visual distractors interfere with tactile temporal order judgment (TOJ) at moderately short stimulus onset asynchronies (SOAs) in typically developing participants. Presentation of a rubber hand in a forward direction to the participant's hand enhances this effect, while that in an inverted direction weakens the effect. Individuals with autism spectrum disorder (ASD) have atypical multisensory processing; however, effects of interferences on atypical multisensory processing in ASD remain unclear. In this study, we examined the effects of visual interference on tactile TOJ in individuals with ASD. Two successive tactile stimuli were delivered to the index and ring fingers of a participant's right hand in an opaque box. A rubber hand was placed on the box in a forward or inverted direction. Concurrently, visual stimuli provided by light-emitting diodes on the fingers of the rubber hand were delivered in a congruent or incongruent order. Participants were required to judge the temporal order of the tactile stimuli regardless of visual distractors. In the absence of a visual stimulus, participants with ASD tended to judge the simultaneous stimuli as the ring finger being stimulated first during tactile TOJ compared with typically developing (TD) controls, and congruent visual stimuli eliminated the bias. When incongruent visual stimuli were delivered, judgment was notably reversed in participants with ASD, regardless of the direction of the rubber hand. The findings demonstrate that there are considerable effects of visual interferences on tactile TOJ in individuals with ASD.

Several motor disabilities accompanied with autism spectrum disorder (ASD) are widely known despite limited reports of underlying neural mechanisms. Gamma-aminobutyric acid (GABA) levels in the motor-related cortical areas modulate several motor performances in healthy participants. We hypothesized that abnormal GABA concentrations in the primary motor area (M1) and supplementary motor area (SMA) associate with different motor difficulties for ASD adolescents/adults. We found that increased GABA concentrations in M1 measured using 1 H-magnetic resonance spectroscopy exhibited lower motor performance in tasks requiring increased muscle strength while lower GABA concentrations in SMA were associated with lower scores in tests measuring body coordination. The degrees of neural inhibition in the M1 and SMA regions would contribute to different dimensions of motor disabilities in autism.

We investigated whether covert ensembles of high- (emotion), and low-level (brightness) visual information, extracted from peripheral faces (presentation/encoding:200 ms), unintentionally influences perception of a central target face stimulus in individuals typically developing (TD) and with autism spectrum condition (ASC). Graded alterations in the summary intensities of the emotion and brightness of the peripheral stimuli modulated the perceptions of the target face in both TD and ASC. In contrast, when we measured goal-directed (overt) ensemble face- emotion and brightness perception, we found that in half of ASC the overt ensemble emotion perception was impaired than TD. Additionally, we repeated both experiments with a backward visual mask to restrict not just encoding but also background processing in the visual system to 200 ms. This revealed that the effect of peripheral ensembles on centre perception was present only with brightness at least in TD but of overt ensembles was evident with both emotion and brightness in TD and ASC alike. These results suggest that while ensemble statistics of low-level information derived automatically and rapidly (200 ms) from contextualized faces are used for target face perception, the same takes longer with high-level information. However, overt facial ensembles are rapidly processed in both TD and ASC.

Prediction is the process by which future events are anticipated based on past events; in contrast, postdiction is the retrospective interpretation of past events based on latter, more recent events. The prediction and postdiction are suggested to be similar based on theoretical models. Previous studies suggest that prediction is impaired in individuals with autism spectrum disorder (ASD). However, it is unclear whether postdiction is also impaired in individuals with ASD. In this study, we evaluated postdiction in individuals with ASD using the cutaneous and stick rabbit illusion paradigms in which the perceived location of a touch shifts postdictively in response to a subsequent touch stimulus. We observed significant cutaneous and stick rabbit illusion in both typically developing (TD) and ASD groups; therefore, postdiction was functional in individuals with ASD. Our present results suggest that postdiction involves a different neuronal process than prediction. We also observed that the ASD group exhibited significantly larger individual difference compared with the TD group in the stick rabbit illusion, which is considered to reflect extension of body schema to external objects. We discuss implications of the individual difference among the ASD participants in the context of sports requiring interactions between the body and external objects.

Many individuals with autism spectrum disorder (ASD) have symptoms of sensory hypersensitivity. Several studies have shown high individual variations in temporal processing of tactile stimuli. We hypothesized that these individual differences are linked to differences in hyper-reactivity among individuals with ASD. Participants performed two tasks as to vibrotactile stimuli: One is a temporal order judgement task, and another is a detection task. We found that individuals with ASD with higher temporal resolution tended to have more severe hypersensitivity symptoms. In contrast, the tactile detection threshold/sensitivity were related to the severities of stereotyped behaviour and restricted interests, rather than to hypersensitivity. Our findings demonstrate that higher temporal resolution to sensory stimuli may contribute to sensory hypersensitivity in individuals with ASD.

Most individuals with autism-spectrum disorders have hypersensitivity/hyposensitivity to various types of sensory stimuli. Although several hypotheses such as higher sensitivity to stimuli, alterations in brain structure and function, and dysfunction of inhibitory systems at the molecular level have been suggested, there is no convincing evidence. We found that individuals with high temporal resolution tended to have strong hypersensitivity to sensory stimuli and vice versa. In addition, we focused on a case with extraordinarily high temporal resolution across the tactile, auditory, and audio-tactile domains. We believe that studying such an extreme case of temporal processing could facilitate an understanding of the neural basis of time perception.

People with autism spectrum disorder (ASD) or higher levels of autistic traits have atypical characteristics in sensory processing. Atypicalities have been reported for proprioceptive judgments, which are tightly related to internal bodily representations underlying position sense. However, no research has directly investigated whether self‐bodily representations are different in individuals with ASD. Implicit hand maps, estimated based on participants' proprioceptive sensations without sight of their hand, are known to be distorted such that the shape is stretched along the medio‐lateral hand axis even for neurotypical participants. Here, with the view of ASD as falling on a continuous distribution among the general population, we explored differences in implicit body representations along with autistic traits by focusing on relationships between autistic traits and the magnitudes of the distortions in implicit hand maps (N ~ 100). We estimated the magnitudes of distortions in implicit hand maps both for fingers and hand surfaces on the dorsal and palmar sides of the hand. Autistic traits were measured by questionnaires (Autism Spectrum [AQ] and Empathy/Systemizing [EQ‐SQ] Quotients). The distortions in implicit hand maps were replicated in our experimental situations. However, there were no significant relationships between autistic traits and the magnitudes of the distortions as well as within‐individual variabilities in the maps and localization performances. Consistent results were observed from comparisons between IQ‐matched samples of people with and without a diagnosis of ASD. Our findings suggest that there exist perceptual and neural processes for implicit body representations underlying position sense consistent across levels of autistic traits. Lay Summary: Atypicalities related to autism spectrum disorder (ASD) have been reported for position sense, our ability to tell where our body parts are even when we cannot see them. People's internal hand images, estimated based on judgments of where different parts of the hands were located without seeing the hand, are shown to be distorted against the physical shapes, even in the general population. We investigated relationships between autistic traits and the distortions in internal hand images in the general population. We found no significant relationships between these measurements. Consistent results were observed from comparisons between people with and without ASD. These findings suggest that the perceptual and neural processes for internal body images are consistent across different levels of autistic traits. [ABSTRACT FROM AUTHOR]

The human brain is sensitive to incoming sensory information across multiple time scales. Temporal scales of information represented in the brain generally constrain behavior. Despite reports of the neural correlates of millisecond timing, how the human brain processes sensory stimuli in the sub-second range (≤100 ms) and its behavioral implications are areas of active scientific inquiry. An autism spectrum disorder (ASD) patient showed a tactile discrimination threshold of 6.49 ms on a temporal order judgment (TOJ) task which was approximately 10-fold superior than other ASD and healthy controls (59 and 69 ms, respectively). To investigate the brain regions of this extremely high temporal resolution in the patient, we used functional magnetic resonance imaging (fMRI) during TOJ. We observed greater activity notably in the left superior temporal gyrus (STG) and precentral gyrus (PrG) compared to that of controls. Generally, the left superior frontal gyrus (SFG) correlated positively, while the opercular part of right inferior frontal gyrus (IFG) correlated negatively, with the correct TOJ rate across all subjects (the patient + 22 healthy controls). We found that the performance was negatively correlated with the strength of neural responses in the right IFG overall in 30 participants (the patient + 22 healthy and 7 ASD controls). Our data reveal superior ability of this particular case of ASD in the millisecond scale for sensory inputs. We highlight several neural correlates of TOJ underlying the facilitation and/or inhibition of temporal resolution in humans. [ABSTRACT FROM AUTHOR]