Souta Hidaka

Introduction Various genetic mutations have been implicated in autism spectrum disorder (ASD). Some candidate genes for ASD are known to be related to signal transduction and may be involved in hand development as well as neurodevelopment. Therefore, although subtle, anatomical variations in hand configurations may be observed in individuals with ASD. However, except for research on the finger ratio, which has been suggested to be related to prenatal sex hormone exposure, only few studies have been conducted. Given the spectrum characteristics of ASD, we explored whether hand configurations are associated with ASD-related traits in the general population. Methods Photographs of the dorsal surface of each hand were obtained, and the distances between the metacarpophalangeal joints and finger lengths were measured. The Autism Spectrum Quotient, Empathy Quotient, and Systemizing Quotient were used to evaluate ASD-related traits. Results We found a significant positive correlation between the aspect ratio of the right hand and the Systemizing Quotient score: individuals with a larger width relative to the finger length showed more systemizing traits. Discussion These findings suggest that gene polymorphisms or prenatal sex hormone exposure may underlie the relationship between systemizing traits and hand configurations.

Abstract 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.

Abstract 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.

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural orientation selectivity has been reported in somatosensory cortices. However, little research has investigated the perceptual characteristics of the tactile TAE. The aim of the current study was to provide the first demonstration of a tactile TAE on the hand and investigate the perceptual nature of tactile TAE on the hand surface. We used a 2-point stimulation with minimal input for orientation. We found clear TAEs on the hand surface: Adaptation induced shifts in subjective vertical sensation toward the orientation opposite to the adapted orientation. Further, adaptation aftereffects were purely based on orientation processing given that the effects transferred between different lengths across adaptor and test stimuli and type of stimuli. Finally, adaptation aftereffects were anchored to the hand: tactile TAE occurred independently of hand rotation and transferred from palm to dorsum sides of the hand, while the effects did not transfer between hands. Our findings demonstrate the existence of hand-centered perceptual processing for basic tactile orientation information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

<title>Abstract</title>Our bodily sensation is a fundamental cue for our self-consciousness. Whereas experimental studies have uncovered characteristics of bodily sensation, these studies investigated bodily sensations through manipulating bodily sensations to be apart from one’s own body and to be assigned to external, body-like objects. In order to capture our bodily sensation as it is, this questionnaire survey study explored the characteristics of bodily sensation using a large population-based sample (<italic>N</italic> = 580, comprising 20s to 70s age groups) without experimental manipulations. We focused on the sensations of ownership, the feeling of having a body part as one’s own, and agency, the feeling of controlling a body part by oneself, in multiple body parts (the eyes, ears, hands, legs, nose, and mouth). The ownership and agency sensations were positively related to each other in each body part. Interestingly, the agency sensation of the hands and legs had a positive relationship with the ownership sensations of the other body parts. We also found the 60s age group had a unique internal configuration, assessed by the similarity of rating scores, of the body parts for each bodily sensation. Our findings revealed the existence of unique characteristics for bodily sensations in a natural state.

Perceptual completion is a fundamental perceptual function serving to maintain robust perception against noise. For example, we can perceive a vivid experience of motion even for the discrete inputs across time and space (apparent motion: AM). In vision, stimuli irrelevant to AM perception are suppressed to maintain smooth AM perception along the AM trajectory where no physical inputs are applied. We investigated whether such perceptual masking induced by perceptual completion of dynamic inputs is general across sensory modalities by focusing on touch. Participants tried to detect a vibro-tactile target stimulus presented along the trajectory of AM induced by two other tactile stimuli on the forearm. In a control condition, the inducing stimuli were applied simultaneously, resulting in no motion percept. Tactile target detection was impaired with tactile AM. Our findings support the notion that the perceptual masking induced by perceptual completion mechanism of AM is a general function rather than a sensory specific effect.

Spatial distortions in touch have been investigated since the 19th century. For example, two touches applied to the hand dorsum feel farther apart when aligned with the mediolateral axis (i.e., across the hand) than when aligned with the proximodistal axis (along the hand). Stimulations to our sensory receptors are usually dynamic, where spatial and temporal inputs closely interact to establish our percept. For example, physically bigger tactile stimuli are judged to last longer than smaller stimuli. Given such links between space and time in touch, we investigated whether there is a tactile anisotropy in temporal perception analogous to the anisotropy described above. In this case, the perceived duration between the onset of two touches should be larger when they are aligned with the mediolateral than with the proximodistal axis of the hand dorsum. To test this hypothesis, we asked participants to judge which of two tactile temporal sequences, having the same spatial separation along and across the dorsum, felt longer. A clear anisotropy of the temporal perception was observed: temporal intervals across the hand were perceived as longer than those along the hand. Consistent with the spatial anisotropy, the temporal anisotropy did not appear on the palm side of the hand, indicating that the temporal anisotropy was based on perceptual processes rather than top-down modulations such as attentional or decisional/response biases. Contrary to our predictions, however, we found no correlation between the magnitudes of the temporal and spatial anisotropies. Our results demonstrated a novel type of temporal illusion in touch, which is strikingly similar in nature to the previously reported spatial anisotropy. Thus, qualitatively similar distorted somatosensory representations appear to underlie both temporal and spatial processing of touch.

Recent studies have demonstrated that mental representations of the hand dorsum are distorted even for healthy participants. Perceptual hand maps estimated by pointing to specific landmarks (e.g., knuckles and tips of fingers) is stretched and shrunk along the medio-lateral and the proximo-distal axes, respectively. Similarly, tactile distance perception between two touches is longer along the medio-lateral axis than the proximo-distal axis. The congruency of the two types of distortions suggests that common perceptual and neural representations may be involved in these processes. Prolonged stimulation by two simultaneous touches having a particular distance can bias subsequent perception of tactile distances (e.g., adaptation to a long distance induces shorter stimuli to be perceived even shorter). This tactile distance adaptation aftereffect has been suggested to occur based on the modulations of perceptual and neural responses at low somatosensory processing stages. The current study investigated whether tactile distance adaptation aftereffects affect also the pattern of distortions on the perceptual hand maps. Participants localized locations on the hand dorsum cued by tactile stimulations (Experiment 1) or visually presented landmarks on a hand silhouette (Experiment 2). Each trial was preceded by adaptation to either a small (2 cm) or large (4 cm) tactile distance. We found clear tactile distance aftereffects. However, no changes were observed for the distorted pattern of the perceptual hand maps following adaptation to a tactile distance. Our results showed that internal body representations involved in perceptual distortions may be distinct between tactile distance perception and the perceptual hand maps underlying position sense.

Crossmodal studies have reported not only facilitatory but also inhibitory perceptual interactions. For instance, tactile stimulation to the index finger of a hand leads to the degradation of visual discrimination performance (touch-induced visual suppression, TIVS). It has been suggested that the magnitude of TIVS depends on the spatial congruency of visuo-tactile stimuli and on individual differences in task performance. We performed a detailed investigation of the effects of spatial consistency and individual differences on the occurrence of TIVS. The visual target and tactile stimulus were presented at co-localized, ipsilateral but not co-localized, or contralateral positions. The degree of autistic traits has been reported to be well variable among the general population and to reflect differences in sensory processing. Therefore, we assessed the magnitude of autistic traits using the autism-spectrum quotient (AQ) as an index of individual differences. TIVS occurred particularly at the ipsilateral but not co-localized position. In contrast, the magnitude of the TIVS was positively correlated with the AQ score when the stimuli were presented at the co-localized position. These findings suggest that the occurrence of TIVS can be modulated both by the spatial relationship between the visual and tactile stimuli and by individual differences in autistic traits.

When we hold thin metallic bars between the palms of our hands and rub the palms against each other, the feeling of touching smooth velvet occurs. Previous studies have shown that tactile motion and pressure on the palms are important for this velvet hand illusion. Interestingly, when we experience this illusion, we cannot feel the texture of our palms as we usually do. In the present study, we investigated the possibility that tactile masking contributes to the occurrence of the velvet hand illusion. We measured vibrotactile detection performance on the palms of the hands during the occurrence of the velvet hand illusion. The detection performance was worse when the illusion occurred than when it did not. Moreover, the degradation of the detection performance correlated positively with the subjective magnitude of the illusion. We also examined whether additional surface texture could affect the occurrence of the illusion and found that the illusion became weaker as the roughness of the surface increased. These findings suggest that tactile motion and pressure information delivered by the bars of smooth surface mask tactile sensations on the palms of the hands, resulting in an illusory smooth, frictionless feeling on the palms.

In relation to the recent development of ultra high definition imaging technique (4K)<br> that have quadruple amount of pixels relative to high definition imaging (HD), it has<br> been reported that observer's subjective impression differ between these imaging. The<br> present study examined how differences in resolution (4K and HD imaging) influence<br> subjective impressions of movies in association with movie contents (natural/artificial<br> objects) and fields of view (wide/medium/narrow) (Exp1). We also investigated the<br> effects of the quantities of motion on subjective impressions of movies in different im-<br>ge resolutions with the flame rate higher (59.94 fps) than the previous study (23.98<br> fps) (Exp2). We found that 4K movies, as compared to HD movies, induced stronger<br> impressions regarding evaluation and comfort especially when they were presented with<br> natural scene and/or larger field of view. It was also shown that 4K movies with higher<br> flame rate induced stronger impressions regarding desirability and comfort regardless<br> of motion quantities, contrary to the previous finding that 4K movies with the larger<br> quantities of motion gave observer lower impression regarding desirability and comfort<br> than HD movies. These results demonstrate that the differences in image resolution<br> could modulate subjective impressions of movies in accordance with the differences in<br> movie contents, fields of view, and flame rate. Moreover, the current findings suggest<br> that there exist some desirable conditions under which the ultra high definition imaging<br> could effectively enhance observers' subjective impressions of movies.<br>

Ultra-high definition (4K) imaging allows us to achieve considerably higher image quality than would high definition (HD) imaging. The present study examined how 4K and HD imaging could influence subjective impressions of movies differently, in association with the quantities of motion and fields of view of these movies. We found that stronger impressions regarding comfort and impact were evoked for 4K movies with smaller quantities of motion and medium field of view. Stronger perceptions of impact occurred for HD movies with larger quantities of motion and larger field of view. HD movies also gave stronger impression regarding dynamics regardless of motion quantities. Additionally, HD movies down-converted from 4K movies tended to induce higher impressions regarding evaluation and comfort in some situations. These results suggest that subjective impressions of movies are influenced by the differences in resolution images, as well as interactions between imaging types and characteristics of movie contents.

For virtual reality systems, the enhancement of a sense of presence (a subjective experience of being in one place even when one is physically situated in another) has been the most important issue. Both theoretically and empirically, the sense of presence has been found to relate dominantly to background components contained in a scene. In contrast, the reality or virtuality which can be assumed to link essentially to foreground components in a scene has not been investigated in detail. The present study defined the latter type of sense as vraisemblance (verisimilitude), and made an exploratory investigation into spatio-temporal characteristics responsible for the higher vraisemblance by using a scene containing Shishi-odoshi (a traditional Japanese fountain made of bamboos) in a Japanese garden as audio-visual stimuli. In Experiment 1, the effects of the field size of view and the sound pressure level of the background were investigated. Higher vraisemblance was observed with the middle field size of view with the original sound pressure level of the background, whereas higher sense of presence was observed with the larger field size of view with the larger background sound. In Experiment 2, the effect of temporal asynchrony between the foreground audio-visual stimuli produced by Shishi-odoshi was investigated. The results show that the range of temporal-window for the audio-visual stimuli necessary for high vraisemblance was different from those for high presence. These findings suggest that the sense of vraisemblance can be distinguishable from the sense of presence, and deeply involved to the foreground-based aesthetic impression in a scene.