Perceptual error based on Bayesian cue combination drives implicit motor adaptation.

The sensorimotor system can recalibrate itself without our conscious awareness, a type of procedural learning whose computational mechanism remains undefined. Recent findings on implicit motor adaptation, such as over-learning from small perturbations and fast saturation for increasing perturbation size, challenge existing theories based on sensory errors. We argue that perceptual error, arising from the optimal combination of movement-related cues, is the primary driver of implicit adaptation. Central to our theory is the increasing sensory uncertainty of visual cues with increasing perturbations, which was validated through perceptual psychophysics (Experiment 1). Our theory predicts the learning dynamics of implicit adaptation across a spectrum of perturbation sizes on a trial-by-trial basis (Experiment 2). It explains proprioception changes and their relation to visual perturbation (Experiment 3). By modulating visual uncertainty in perturbation, we induced unique adaptation responses in line with our model predictions (Experiment 4). Overall, our perceptual error framework outperforms existing models based on sensory errors, suggesting that perceptual error in locating one's effector, supported by Bayesian cue integration, underpins the sensorimotor system's implicit adaptation.

Abnormalities in motor adaptation to different types of perturbations in schizophreniaperturbations in schizophrenia.

Schizophrenia is a mental health disorder that often includes psychomotor disturbances, impacting how individuals adjust their motor output based on the cause of motor errors. While previous motor adaptation studies on individuals with schizophrenia have largely focused on large and consistent perturbations induced by abrupt experimental manipulations, such as donning prism goggles, the adaptation process to random perturbations, either caused by intrinsic motor noise or external disturbances, has not been examined - despite its ecological relevance. Here, we used a unified behavioral task paradigm to examine motor adaptation to perturbations of three causal structures among individuals in the remission stage of schizophrenia, youth with ultra-high risk of psychosis, adults with active symptoms, and age-matched controls. Results showed that individuals with schizophrenia had reduced trial-by-trial adaptation and large error variance when adapting to their own motor noise. When adapting to random but salient perturbations, they showed intact adaptation and normal causal inference of errors. This contrasted with reduced adaptation to large yet consistent perturbations, which could reflect difficulties in forming cognitive strategies rather than the often-assumed impairments in procedural learning or sense of agency. Furthermore, the observed adaptation effects were correlated with the severity of positive symptoms across the diagnosis groups. Our findings suggest that individuals with schizophrenia face challenges in accommodating intrinsic perturbations when motor errors are ambiguous but adapt with intact causal attribution when errors are salient.

Neural correlates of an illusionary sense of agency caused by virtual reality.

Sense of agency (SoA) is the sensation that self-actions lead to ensuing perceptual consequences. The prospective mechanism emphasizes that SoA arises from motor prediction and its comparison with actual action outcomes, while the reconstructive mechanism stresses that SoA emerges from retrospective causal processing about the action outcomes. Consistent with the prospective mechanism, motor planning regions were identified by neuroimaging studies using the temporal binding (TB) effect, a behavioral measure often linked to implicit SoA. Yet, TB also occurs during passive observation of another's action, lending support to the reconstructive mechanism, but its neural correlates remain unexplored. Here, we employed virtual reality (VR) to modulate such observation-based SoA and examined it with functional magnetic resonance imaging (fMRI). After manipulating an avatar hand in VR, participants passively observed an avatar's "action" and showed a significant increase in TB. The binding effect was associated with the right angular gyrus and inferior parietal lobule, which are critical nodes for inferential and agency processing. These results suggest that the experience of controlling an avatar may potentiate inferential processing within the right inferior parietal cortex and give rise to the illusionary SoA without voluntary action.

Gravity matters for the neural representations of action semantics.

The dynamic relationship between the neural representation of action word semantics and specific sensorimotor experience remains controversial. Here, we temporarily altered human subjects' sensorimotor experience in a 15-day head-down tilt bed rest setting, a ground-based analog of microgravity that disproportionally affects sensorimotor experiences of the lower limbs, and examined whether such effector-dependent activity deprivation specifically affected the neural processes of comprehending verbs of lower-limb actions (e.g. to kick) relative to upper-limb ones (e.g. to pinch). Using functional magnetic resonance imaging, we compared the multivoxel neural patterns for such action words prior to and after bed rest. We found an effector-specific (lower vs. upper limb) experience modulation in subcortical sensorimotor-related and anterior temporal regions. The neural action semantic representations in other effector-specific verb semantic regions (e.g. left lateral posterior temporal cortex) and motor execution regions were robust against such experience alterations. These effector-specific, sensorimotor-experience-sensitive and experience-independent patterns of verb neural representation highlight the multidimensional and dynamic nature of semantic neural representation, and the broad influence of microgravity (hence gravity) environment on cognition.

Atypical development of social and nonsocial working memory capacity among preschoolers with autism spectrum disorders.

Individuals with autism spectrum disorders (ASD) have shown impaired performance in canonical and nonsocial working memory (WM). However, no study has investigated social WM and its early development. Using biological motion stimuli, our study assessed the development of social and nonsocial WM capacity among children with or without ASD across the age span between 4 and 6 (N = 150). While typically developing (TD) children show a rapid development from age 5 to 6, children with ASD showed a delayed development for both social and nonsocial WM capacity, reaching a significant group difference at age 6. Furthermore, we found a negative correlation between social (but not nonsocial) WM capacity and the severity of autistic symptoms among children with ASD. In contrast, there is a positive correlation between both types of WM capacity and intelligence among TD children but not among children with ASD. Our findings thus indicate that individuals with ASD miss the rapid development of WM capacity in early childhood and, particularly, their delayed social WM development might contribute to core symptoms that critically depend on social information processing.

Transcranial Direct-Current Stimulation Does Not Affect Implicit Sensorimotor Adaptation: A Randomized Sham-Controlled Trial.

Humans constantly calibrate their sensorimotor system to accommodate environmental changes, and this perception-action integration is extensively studied using sensorimotor adaptation paradigms. The cerebellum is one of the key brain regions for sensorimotor adaptation, but previous attempts to modulate sensorimotor adaptation with cerebellar transcranial direct current stimulation (ctDCS) produced inconsistent findings. Since both conscious/explicit learning and procedural/implicit learning are involved in adaptation, researchers have proposed that ctDCS only affects sensorimotor adaptation when implicit learning dominates the overall adaptation. However, previous research had both types of learning co-exist in their experiments without controlling their potential interaction under the influence of ctDCS. Here, we used error clamp perturbation and gradual perturbation, two effective techniques to elicit implicit learning only, to test the ctDCS effect on sensorimotor adaptation. We administrated ctDCS to independent groups of participants while they implicitly adapted to visual errors. In Experiment 1, we found that cerebellar anodal tDCS had no effect on implicit adaptation induced by error clamp. In Experiment 2, we applied both anodal and cathodal stimulation and used a smaller error clamp to prevent a potential ceiling effect, and replicated the null effect. In Experiment 3, we used gradually imposed visual errors to elicit implicit adaptation but still found no effect of anodal tDCS. With a total of 174 participants, we conclude that the previous inconsistent tDCS effect on sensorimotor adaptation cannot be explained by the relative contribution of implicit learning. Given that the cerebellum is simultaneously involved in explicit and implicit learning, our results suggest that the complex interplay between the two learning processes and large individual differences associated with this interplay might contribute to the inconsistent findings from previous studies on ctDCS and sensorimotor adaptation.

Pupil-Linked Arousal Response Reveals Aberrant Attention Regulation among Children with Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a developmental disorder that is characterized by difficulties with social interaction and interpersonal communication. It has been argued that abnormal attentional function to exogenous stimuli precedes and contributes to the core ASD symptoms. Notably, the locus ceruleus (LC) and its noradrenergic projections throughout the brain modulate attentional function, but the extent to which this locus ceruleus-norepinephrine (LC-NE) system influences attention in individuals with ASD, who frequently exhibit dysregulated alerting and attention orienting, is unknown. We examined dynamic attention control in girls and boys with ASD at rest using the pupil dilation response (PDR) as a noninvasive measure of LC-NE activity. When gender- and age-matched neurotypical participants were passively exposed to an auditory stream, their PDR decreased for recurrent stimuli but remained sensitive to surprising deviant stimuli. In contrast, children with ASD showed less habituation to recurrent stimuli as well as a diminished phasic response to deviants, particularly those containing social information. Their tonic habituation impairment predicts their phasic orienting impairment, and both impairments correlated with the severity of ASD symptom. Because of the fact that these pupil-linked responses are observed when individuals passively listen without any task engagement, our findings imply that the intricate and dynamic attention allocation mechanism, mediated by the subcortical LC-NE system, is impaired in ASD.SIGNIFICANCE STATEMENT Autistic individuals show attentional abnormalities to even simple sensory inputs, which emerge even before formal diagnosis. One possible mechanism behind these abnormalities is a malfunctioning pacemaker of their attention system, the locus ceruleus-norepinephrine pathway. Here we found, according to the pupillary response (a noradrenergic activity proxy), autistic children are hypersensitive to repeated sounds but hyposensitive to surprising deviant sounds when compared with age-matched controls. Importantly, hypersensitivity to repetitions predicts hyposensitivity to deviant sounds, and both abnormalities positively correlate to the severity of autistic symptoms. This provides strong evidence that autistic children have faulty noradrenergic regulation, which might underly the attentional atypicalities previously evidenced in various cortical responses in autistic individuals.

Improving postural stability among people with lower-limb amputations by tactile sensory substitution.

BACKGROUND: For people with lower-limb amputations, wearing a prosthetic limb helps restore their motor abilities for daily activities. However, the prosthesis's potential benefits are hindered by limited somatosensory feedback from the affected limb and its prosthesis. Previous studies have examined various sensory substitution systems to alleviate this problem; the prominent approach is to convert foot-ground interaction to tactile stimulations. However, positive outcomes for improving their postural stability are still rare. We hypothesized that the sensory substiution system based on surrogated tactile stimulus is capable of improving the standing stability among people with lower-limb amputations. METHODS: We designed a wearable device consisting of four pressure sensors and two vibrators and tested it among people with unilateral transtibial amputations (n = 7) and non-disabled participants (n = 8). The real-time measurements of foot pressure were fused into a single representation of foot-ground interaction force, which was encoded by varying vibration intensity of the two vibrators attached to the participants' forearm. The vibration intensity followed a logarithmic function of the force representation, in keeping with principles of tactile psychophysics. The participants were tested with a classical postural stability task in which visual disturbances perturbed their quiet standing. RESULTS: With a brief familiarization of the system, the participants exhibited better postural stability against visual disturbances when switching on sensory substitution than without. The body sway was substantially reduced, as shown in head movements and excursions of the center of pressure. The improvement was present for both groups of participants and was particularly pronounced in more challenging conditions with larger visual disturbances. CONCLUSIONS: Substituting otherwise missing foot pressure feedback with vibrotactile signals can improve postural stability for people with lower-limb amputations. The design of the mapping between the foot-ground interaction force and the tactile signals is essential for the user to utilize the surrogated tactile signals for postural control, especially for situations that their postural control is challenged.

Sensorimotor knowledge from task-irrelevant feedback contributes to motor learning.

Exposure to task-irrelevant feedback leads to perceptual learning, but its effect on motor learning has been understudied. Here, we asked human participants to reach a visual target with a hand-controlled cursor while observing another cursor moving independently in a different direction. Although the task-irrelevant feedback did not change the main task's performance, it elicited robust savings in subsequent adaptation to classical visuomotor rotation perturbation. We demonstrated that the saving effect resulted from a faster formation of strategic learning through a series of experiments, not from gains in the implicit learning process. Furthermore, the saving effect was robust against drastic changes in stimulus features (i.e., rotation size or direction) or task types (i.e., for motor adaptation and skill learning). However, the effect was absent when the task-irrelevant feedback did not carry the visuomotor relationship embedded in visuomotor rotation. Thus, though previous research on perceptual learning has related task-irrelevant feedback to changes in early sensory processes, our findings support its role in acquiring abstract sensorimotor knowledge during motor learning. Motor learning studies have traditionally focused on task-relevant feedback, but our study extends the scope of feedback processes and sheds new light on the dichotomy of explicit and implicit learning in motor adaptation and motor structure learning.NEW & NOTEWORTHY When the motor system faces perturbations, such as fatigue or new environmental changes, it adapts to these changes by voluntarily selecting new action plans or implicitly fine-tuning the control. We show that the action selection part can be enhanced without practice or explicit instruction. We further demonstrate that this enhancement is probably linked to the acquisition of abstract knowledge about the to-be-adapted novel visual feedback. Our findings draw an interesting parallel between motor and perceptual learning by showing that top-down information affects both types of procedural learning.

Automatic classification of children with autism spectrum disorder by using a computerized visual-orienting task.

Early screening and diagnosis of autism spectrum disorder (ASD) primarily rely on behavioral observations by qualified clinicians whose decision process can benefit from the combination of machine learning algorithms and sensor data. We designed a computerized visual-orienting task with gaze-related or non-gaze-related directional cues, which triggered participants' gaze-following behavior. Based on their eye-movement data registered by an eye tracker, we applied the machine learning algorithms to classify high-functioning children with ASD (HFA), low-functioning children with ASD (LFA), and typically developing children (TD). We found that TD children had higher success rates in obtaining rewards than HFA children, and HFA children had higher rates than LFA children. Based on raw eye-tracking data, our machine learning algorithm could classify the three groups with an accuracy of 81.1% and relatively high sensitivity and specificity. Classification became worse if only data from the gaze or nongaze conditions were used, suggesting that "less-social" directional cues also carry useful information for distinguishing these groups. Our findings not only provide insights about visual-orienting deficits among children with ASD but also demonstrate the promise of combining classical behavioral paradigms with machine learning algorithms for aiding the screening for individuals with ASD.

Examining modifications of execution strategies during a continuous task.

How strategies are formulated during a performance is an important aspect of motor control. Knowledge of the strategy employed in a task may help subjects achieve better performances, as it would help to evidence other possible strategies that could be used as well as help perfect a certain strategy. We sought to investigate how much of a performance is conditioned by the initial state and whether behavior throughout the performance is modified within a short timescale. In other words, we focus on the process of execution and not on the outcome. To this scope we used a repeated continuous circle tracing task. Performances were decomposed into different components (i.e., execution variables) whose combination is able to numerically determine movement outcome. By identifying execution variables of speed and duration, we created an execution space and a solution manifold (i.e., combinations of execution variables yielding zero discrepancy from the desired outcome) and divided the subjects according to their initial performance in that space into speed preference, duration preference, and no-preference groups. We demonstrated that specific strategies may be identified in a continuous task, and strategies remain relatively stable throughout the performance. Moreover, as performances remained stable, the initial location in the execution space can be used to determine the subject's strategy. Finally, contrary to other studies, we demonstrated that, in a continuous task, performances were associated with reduced exploration of the execution space.

Accuracy of hand localization is subject-specific and improved without performance feedback.

Accumulating evidence indicates that the spatial error of human's hand localization appears subject-specific. However, whether the idiosyncratic pattern persists across time with good within-subject consistency has not been adequately examined. Here we measured the hand localization map by a Visual-matching task in multiple sessions over 2 days. Interestingly, we found that participants improved their hand localization accuracy when tested repetitively without performance feedback. Importantly, despite the reduction of average error, the spatial pattern of hand localization errors remained idiosyncratic. Based on individuals' hand localization performance, a standard convolutional neural network classifier could identify participants with good accuracy. Moreover, we did not find supporting evidence that participants' baseline hand localization performance could predict their motor performance in a visual Trajectory-matching task even though both tasks require accurate mapping of hand position to visual targets in the same workspace. Using a separate experiment, we not only replicated these findings but also ruled out the possibility that performance feedback during a few familiarization trials caused the observed improvement in hand localization. We conclude that the conventional hand localization test itself, even without feedback, can improve hand localization but leave the idiosyncrasy of hand localization map unchanged.

"I Dreamed of My Hands and Arms Moving Again": A Case Series Investigating the Effect of Immersive Virtual Reality on Phantom Limb Pain Alleviation.

Phantom limb pain (PLP) is a type of chronic pain that follows limb amputation, brachial plexus avulsion injury, or spinal cord injury. Treating PLP is a well-known challenge. Currently, virtual reality (VR) interventions are attracting increasing attention because they show promising analgesic effects. However, most previous studies of VR interventions were conducted with a limited number of patients in a single trial. Few studies explored questions such as how multiple VR sessions might affect pain over time, or if a patient's ability to move their phantom limb may affect their PLP. Here we recruited five PLP patients to practice two motor tasks for multiple VR sessions over 6 weeks. In VR, patients "inhabit" a virtual body or avatar, and the movements of their intact limbs are mirrored in the avatar, providing them with the illusion that their limbs respond as if they were both intact and functional. We found that repetitive exposure to our VR intervention led to reduced pain and improvements in anxiety, depression, and a sense of embodiment of the virtual body. Importantly, we also found that their ability to move their phantom limbs improved as quantified by shortened motor imagery time with the impaired limb. Although the limited sample size prevents us from performing a correlational analysis, our findings suggest that providing PLP patients with sensorimotor experience for the impaired limb in VR appears to offer long-term benefits for patients and that these benefits may be related to changes in their control of the phantom limbs' movement.

Abnormal Gait Patterns in Autism Spectrum Disorder and Their Correlations with Social Impairments.

Ground walking in humans is typically stable, symmetrical, characterized by smooth heel-to-toe ground contact. Previous studies on children with autism spectrum disorder (ASD) identified various gait abnormalities. However, they produced inconsistent findings, particularly for the occurrence of toe walking and gait symmetry between feet, owing to their reliance on retrospective reports, visual analysis of videos, or kinematic analysis of the gait. The present study examined gait functions in children with ASD using plantar pressure that quantified foot-ground interaction with high spatial and temporal resolutions. Fifty-eight 4-6-year-old children with ASD (12 low-functioning and 46 high-functioning autism) and 28 age-matched typically developed children walked straight 6 m at their preferred speed for 10 repetitions. We found that both ASD groups walked with more flat-footed contact pattern, more left-right asymmetry, and larger step-to-step variability than their controls. Furthermore, these abnormal gait characteristics were related to social impairments measured by the Autism Spectrum Quotient and Social Responsive Scale, supporting a close association between impaired motor coordination and core symptoms of autism. Autism Res 2020, 13: 1215-1226. © 2020 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: We examined gait functions among children with autism by measuring their foot plantar pressure during simple straight walking. Children with ASD walked with a characteristic foot-ground contact pattern with inappropriate contact forces and large step-to-step variability when compared with their age-matched controls. These walking abnormalities were dependent on their social impairments but independent from their intelligence, indicating a close relationship between atypical motor coordination and core symptoms of autism.

Target selection by gaze pointing and manual confirmation: performance improved by locking the gaze cursor.

Eye movement-based human-computer interactions are emerging in diverse scenarios. When selecting targets on a user interface, the method of combining fast gaze pointing with reliable manual action is becoming increasingly popular. However, this method suffers from noise in gaze pointing caused by eye jitters and users' habitual early move-away of gaze before manual actions. Here we propose a novel solution to mitigate these problems by locking the gaze cursor at the target for imminent manual selection. We compared this gaze-lock cursor with a conventional gaze cursor in a typing task with varying key sizes and key gaps. Results show that typing performance was significantly better with larger key size and gap. More importantly, the gaze-lock cursor significantly increased speed and decreased errors when compared to a conventional gaze cursor. Our findings demonstrate that the gaze-lock cursor is a promising tool for gaze interactions involving frequent target selections. Practitioner summary: Target selection by gaze pointing and manual confirmation suffers from eye jitters and users' habitual early move-away of gaze before manual actions. The performance of this method can be improved by applying the gaze-lock cursor we proposed, increasing target size or increasing the target gap. Abbreviations: WTC: warping to target center; ALCM: automatic lock of cursor movement; LCD: liquid crystal display; EWMA: exponential weighted moving average; ER: error rate; ET: execution time; ED: edit distance; CV: coefficients of variation; ANOVA: analysis of variance; GUIs: general user interfaces.

Savings in sensorimotor adaptation without an explicit strategy.

The hallmark of long-term retention of sensorimotor adaptation is a faster relearning when similar perturbations are encountered again. However, what processes underlie this saving effect is in debate. Though motor adaptation is traditionally viewed as a type of procedural learning, its savings has been recently shown to be solely based on a quick recall of explicit adaptation strategy. Here, we showed that adaptation to a novel error-invariant perturbation without an explicit strategy could enable subsequent savings. We further showed that adaptation to gradual perturbations could enable savings, which was supported by enhanced implicit learning. Our study provides supporting evidence that long-term retention of motor adaptation is possible without forming or recalling a cognitive strategy, and the interplay between implicit and explicit learning critically depends on the specifics of learning protocol and available sensory feedback.NEW & NOTEWORTHY Savings in motor learning sometimes refers to faster learning when one encounters the same perturbation again. Previous studies assert that forming a cognitive strategy for countering perturbations is necessary for savings. We used novel experimental techniques to prevent the formation of a cognitive strategy during initial adaptation and found that savings still existed during relearning. Our findings suggest that savings in sensorimotor adaptation do not exclusively depend on forming and recalling an explicit strategy.

Visuomotor perturbation in a continuous circle tracing task: novel approach for quantifying motor adaptation.

The study of motor adaptation certainly has advanced greatly through the years and helped to shed light on the mechanisms of motor learning. Most paradigms used to study adaptation employ a discrete approach, where people adapt in successive attempts. Continuous tasks on the other hand, while known to possess different characteristics than discrete ones, have received little attention regarding the study motor adaptation. In this paper, we test for adaptation using a continuous circle tracing task with a visuomotor gain perturbation. To examine the feasibility of this task, 45 normal subjects divided into 3 groups were tested for adaptation, aftereffects, and generalization. All subjects exhibited a gradual adaptation when faced with a perturbation as well as opposite aftereffects once the perturbation was removed. Aftereffects tended to persist unless veridical feedback was given. The task generalized well both in size and in space. We believe that this task, by being continuous, could allow for a thorough investigation of visuomotor adaptation to gain perturbations in particular, and perhaps be expanded to other types of adaptations as well, especially when used alongside discrete tasks.

Pose estimates from online videos show that side-by-side walkers synchronize movement under naturalistic conditions.

Marker-less video-based pose estimation promises to allow us to do movement science on existing video databases. We revisited the old question of how people synchronize their walking using real world data. We thus applied pose estimation to 348 video segments extracted from YouTube videos of people walking in cities. As in previous, more constrained, research, we find a tendency for pairs of people to walk in phase or in anti-phase with each other. Large video databases, along with pose-estimation algorithms, promise answers to many movement questions without experimentally acquiring new data.

Sensorimotor priors are effector dependent.

During sensorimotor tasks, subjects use sensory feedback but also prior information. It is often assumed that the sensorimotor prior is just given by the experiment and that the details for acquiring this prior (e.g., the effector) are irrelevant. However, recent research has suggested that the construction of priors is nontrivial. To test if the sensorimotor details matter for the construction of a prior, we designed two tasks that differ only in the effectors that subjects use to indicate their estimate. For both a typical reaching setting and an atypical wrist rotation setting, prior and feedback uncertainty matter as quantitatively predicted by Bayesian statistics. However, in violation of simple Bayesian models, the importance of the prior differs across effectors. Subjects overly rely on their prior in the typical reaching case compared with the wrist case. The brain is not naively Bayesian with a single and veridical prior. NEW & NOTEWORTHY Traditional Bayesian models often assume that we learn statistics of movements and use the information as a prior to guide subsequent movements. The effector is merely a reporting modality for information processing. We asked subjects to perform a visuomotor learning task with different effectors (finger or wrist). Surprisingly, we found that prior information is used differently between the effectors, suggesting that learning of the prior is related to the movement context such as the effector involved or that naive models of Bayesian behavior need to be extended.

The uncanny valley effect in typically developing children and its absence in children with autism spectrum disorders.

Robots and virtual reality are gaining popularity in the intervention of children with autism spectrum disorder (ASD). To shed light on children's attitudes towards robots and characters in virtual reality, this study aims to examine whether children with ASD show the uncanny valley effect. We varied the realism of facial appearance by morphing a cartoon face into a human face, and induced perceptual mismatch by enlarging the eyes, which has previously been shown as an effective method to induce the uncanny valley effect in adults. Children with ASD and typically developing (TD) children participated in a two-alternative forced choice task that asked them to choose one they liked more from the two images presented on the screen. We found that TD children showed the effect, i.e., the enlargement of eye size and the approaching realism reduced their preference. In contrast, children with ASD did not show the uncanny valley effect. Our findings in TD children help resolve the controversy in the literature about the existence of the uncanny valley effect among young children. Meanwhile, the absence of the uncanny valley effect in children with ASD might be attributed to their reduced sensitivity to subtle changes of face features and their limited visual experience to faces caused by diminished social motivation. Last, our findings provide practical implications for designing robots and virtual characters for the intervention of children with ASD.