The science of interpersonal touch: an overview

How material sensory properties and individual differences influence the haptic aesthetic appeal of visually presented stimuli

Touch plays a crucial role for humans. Despite its centrality in sensory experiences, the field of haptic aesthetics is underexplored. So far, existing research has revealed that preferences in the haptic domain are related to stimulus properties and the Gestalt laws of grouping. Additionally, haptic aesthetics is influenced by top-down processes, e.g., stimulus familiarity, and is likely to be modulated by personality and expertise. To further our understanding of these influences on haptic aesthetic appraisal, the current study investigated the imagined haptic aesthetic appeal of visually presented material surfaces, considering the role of haptic expertise, Need for touch, personality traits. The results revealed a positive influence of familiarity, simplicity, smoothness, warmth, lightness, dryness, slipperiness and a negative influence of complexity on individuals' aesthetic responses. While the study failed to support the predicted influence of Need for touch and haptic expertise on aesthetic responses, results did reveal an influence of openness to experience, conscientiousness and neuroticism. Despite the limitations related to the indirect stimuli presentation (vision only), the findings contribute to the relatively unexplored role of bottom-up and top-down features in haptic aesthetics that might be incorporated into the design of consumers' products to better meet their preferences.

Choice enhances touch pleasantness

We value what we choose more than what is imposed upon us. Choice-induced preferences are extensively demonstrated using behavioural and neural methods, mainly involving rewarding objects such as money or material goods. However, the impact of choice on experiences, especially in the realm of affective touch, remains less explored. In this study, we specifically investigate whether choice can enhance the pleasure derived from affective touch, thereby increasing its intrinsic rewarding value. We conducted an experiment in which participants were being touched by an experimenter and asked to rate how pleasant their experience of touch was. They were given either a choice or no choice over certain touch stimulus variables which differed in their relevance: some were of low relevance (relating to the colour of the glove that the experimenter would use to touch them), while others were of high relevance (relating to the location on their arm where they would be stroked). Before and during touching, pupillometry was used to measure the level of arousal. We found that having a choice over aspects of tactile stimuli-especially those relevant to oneself-enhanced the pleasant perception of the touch. In addition, having a choice increases arousal in anticipation of touch. Regardless of how relevant it is to the actual tactile stimulus, allowing one to choose may positively enhance a person's perception of the physical contact they receive.

Determinants for positive and negative experiences of interpersonal touch: context matters

The goal of the study was to determine which aspects of interpersonal touch interactions lead to a positive or negative experience. Previous research has focused primarily on physical characteristics. We suggest that this may not be sufficient to fully capture the complexity of the experience. Specifically, we examined how fulfilment of psychological needs influences touch experiences and how this relates to physical touch characteristics and situational factors.In two mixed-method studies, participants described their most positive and most negative interpersonal touch experience within a specific time frame. They reported fulfilment of nine needs, affect, intention, and reason for positivity/negativity, as well as the body part(s) touched, location, type of touch, interaction partner, and particular touch characteristics (e.g. humidity).Positive and negative touch experiences shared similar touch types, locations, and body parts touched, but differed in intended purpose and reasons. Overall, the valence of a touch experience could be predicted from fulfilment of relatedness, the interaction partner and initiator, and physical touch characteristics. Positive affect increased with need fulfilment, and negative affect decreased.The results highlight the importance of relatedness and reciprocity for the valence of touch, and emphasise the need to incorporate psychological needs in touch research.

A modern way to teach and practice manual therapy

BACKGROUND

Musculoskeletal conditions are the leading contributor to global disability and health burden. Manual therapy (MT) interventions are commonly recommended in clinical guidelines and used in the management of musculoskeletal conditions. Traditional systems of manual therapy (TMT), including physiotherapy, osteopathy, chiropractic, and soft tissue therapy have been built on principles such as clinician-centred assessment, patho-anatomical reasoning, and technique specificity. These historical principles are not supported by current evidence. However, data from clinical trials support the clinical and cost effectiveness of manual therapy as an intervention for musculoskeletal conditions, when used as part of a package of care.

PURPOSE

The purpose of this paper is to propose a modern evidence-guided framework for the teaching and practice of MT which avoids reference to and reliance on the outdated principles of TMT. This framework is based on three fundamental humanistic dimensions common in all aspects of healthcare: safety, comfort, and efficiency. These practical elements are contextualised by positive communication, a collaborative context, and person-centred care. The framework facilitates best-practice, reasoning, and communication and is exemplified here with two case studies.

METHODS

A literature review stimulated by a new method of teaching manual therapy, reflecting contemporary evidence, being trialled at a United Kingdom education institute. A group of experienced, internationally-based academics, clinicians, and researchers from across the spectrum of manual therapy was convened. Perspectives were elicited through reviews of contemporary literature and discussions in an iterative process. Public presentations were made to multidisciplinary groups and feedback was incorporated. Consensus was achieved through repeated discussion of relevant elements.

CONCLUSIONS

Manual therapy interventions should include both passive and active, person-empowering interventions such as exercise, education, and lifestyle adaptations. These should be delivered in a contextualised healing environment with a well-developed person-practitioner therapeutic alliance. Teaching manual therapy should follow this model.

Closing the loop in minimally supervised human-robot interaction: formative and summative feedback

Human instructors fluidly communicate with hand gestures, head and body movements, and facial expressions, but robots rarely leverage these complementary cues. A minimally supervised social robot with such skills could help people exercise and learn new activities. Thus, we investigated how nonverbal feedback from a humanoid robot affects human behavior. Inspired by the education literature, we evaluated formative feedback (real-time corrections) and summative feedback (post-task scores) for three distinct tasks: positioning in the room, mimicking the robot's arm pose, and contacting the robot's hands. Twenty-eight adults completed seventy-five 30-s-long trials with no explicit instructions or experimenter help. Motion-capture data analysis shows that both formative and summative feedback from the robot significantly aided user performance. Additionally, formative feedback improved task understanding. These results show the power of nonverbal cues based on human movement and the utility of viewing feedback through formative and summative lenses.

The impact of daily affective touch on cortisol levels in institutionalized & fostered children

Institutionalized children are often deprived of affective touch. Such tactile deprivation often leads to constant stress, as measured by the levels of salivary cortisol. We report here the impact of an affective touch program, optimized to activate a specific population of unmyelinated mechanosensitive nerves in the skin called c-tactile afferents (CT) on stress resistance. Two populations of children (age 4-10) were recruited: (i) a cohort living in an orphanage and (ii) a fostered cohort. Both groups received the affective touch program daily for 10-15 min for 5-6 weeks. A cohort of age-matched children living in a family environment acted as a control group and did not receive any instructions for tactile stimulation. Salivary cortisol was collected at the beginning (T1) and at the end (T2) of the study in all three groups. For institutionalized and fostered children there was a significant improvement in the level of cortisol (p < 0.0001) between T1 and T2, which is manifested in the balancing cortisol levels: a decrease where it was elevated and an increase, where the critically low level testified to the distress of the child. Balancing cortisol levels is a process of recovery to normal values, which indicates the restoration of neurohumoral mechanisms of stress regulation. The effect of balancing cortisol levels was more pronounced in the group of fostered children compared to the group of orphanage children (p = 0.0326). The children in the control group had no significant differences.

Soft Sensors and Actuators for Wearable Human-Machine Interfaces

Haptic human-machine interfaces (HHMIs) combine tactile sensation and haptic feedback to allow humans to interact closely with machines and robots, providing immersive experiences and convenient lifestyles. Significant progress has been made in developing wearable sensors that accurately detect physical and electrophysiological stimuli with improved softness, functionality, reliability, and selectivity. In addition, soft actuating systems have been developed to provide high-quality haptic feedback by precisely controlling force, displacement, frequency, and spatial resolution. In this Review, we discuss the latest technological advances of soft sensors and actuators for the demonstration of wearable HHMIs. We particularly focus on highlighting material and structural approaches that enable desired sensing and feedback properties necessary for effective wearable HHMIs. Furthermore, promising practical applications of current HHMI technology in various areas such as the metaverse, robotics, and user-interactive devices are discussed in detail. Finally, this Review further concludes by discussing the outlook for next-generation HHMI technology.

Modulation of facial muscle responses by another person's presence and affiliative touch during affective image viewing

Stimulating CT-afferents by forearm caresses produces the subjective experience of pleasantness in the receiver and modulates subjective evaluations of viewed affective images. Receiving touch from another person includes the social element of another person's presence, which has been found to influence affective image evaluations without involving touch. The current study investigated whether these modulations translate to facial muscle responses associated with positive and negative affect across touch-involving and mere presence conditions. Female participants (N = 40, M(age) = 22.4, SD = 5.3) watched affective images (neutral, positive, negative) while facial electromyography was recorded (sites: zygomaticus, corrugator). Results from ANOVAs showed that providing touch to another person or oneself modulated zygomaticus site responses when viewing positive images. Providing CT-afferent stimulating touch (i.e., forearm caresses) to another person or oneself dampened the positive affective facial muscle response to positive affective images. Providing touch to another person generally increased corrugator facial muscle activity related to negative affect. Receiving touch did not modulate affective facial muscle responses during the viewing of affective images but may have effects on later cognitive processes. Together, previously reported social and touch modulations of subjective evaluations of affective images do not translate to facial muscle responses during affective image viewing, which were differentially modulated.

An in-depth analysis of the polyvagal theory in light of current findings in neuroscience and clinical research

The polyvagal theory has led to the understanding of the functions of the autonomic nervous system in biological development in humans, since the vagal system, a key structure within the polyvagal theory, plays a significant role in addressing challenges of the mother-child dyad. This article aims to summarize the neurobiological aspects of the polyvagal theory, highlighting some of its strengths and limitations through the lens of new evidence emerging in several research fields-including comparative anatomy, embryology, epigenetics, psychology, and neuroscience-in the 25 years since the theory's inception. Rereading and incorporating the polyvagal idea in light of modern scientific findings helps to interpret the role of the vagus nerve through the temporal dimension (beginning with intrauterine life) and spatial dimension (due to the numerous connections of the vagus with various structures and systems) in the achievement and maintenance of biopsychosocial well-being, from the uterus to adulthood.

Sensory, Affective, and Social Experiences with Haptic Devices in Intramural Care Practice

Previous work has shown that technology can facilitate the communication of emotions, social touch, and social presence through haptic devices, meaning devices that provide a haptic stimulation. However, for special user groups living in long-term care facilities, such as people with dementia, the applications of these haptic devices are not apparent. The aim of this study is to understand how haptic devices can be used in intramural care facilities in times of social isolation, focusing on haptic devices that utilize haptic sensation. Five haptic devices were tested at three care facilities. Insights from this study highlight the potential of haptic devices to enhance sensory, affective, and social experiences during video calling between residents and their relatives. Moreover, the importance of the tactile sensation and form factor of haptic devices in the care context is addressed, along with insights on how to create the appropriate atmosphere during video calling.

Virtually simulated interpersonal touch negatively affects perceived closeness and social affiliation to an avatar partner

Interpersonal touch is an essential component of human non-verbal communication, facilitating social affiliation and bonding. With the widespread use of digital interfaces and online platforms in all realms of human interactions, there are fewer opportunities for communicating through touch. Popular online platforms that virtually simulate human interactions rely primarily on visual and auditory modalities, providing limited or no capacity for the exchange of tactile cues. Previous studies of virtual interactions have explored the simulation of social touch using haptic devices, but little is known about how the visual representation of interpersonal touch is perceived and integrated into a virtual social experience. In two studies we examined how the exchange of virtual touch mediated by simulated 3-dimensional human characters, or avatars, within an online virtual environment influenced affiliation towards an unfamiliar interaction partner. Surprisingly, the exchange of virtual touch negatively affected the perceived closeness and affiliation to the partner and the social evaluation of the interaction but did not affect the level of physiological arousal during the interaction. These results indicate that the visual representation of social touch is sufficient to virtually communicate touch-related cues that impact social affiliation, but the influence of touch may be dependent on the interaction context.

Exploring social touch in autistic and non-autistic adults via a self-report body-painting task: The role of sex, social context and body area

LAY ABSTRACT

What is already known about the topic?At least in neurotypical individuals, social touch represents an important channel for emotional communication associated with social bonding and pain/anxiety modulation. Autistic adults report to avoid social touch more and to have different tactile sensitivity than their non-autistic comparisons.What this paper adds?Few studies specifically investigated social touch in autistic individuals, and none of them examined the role of participants' sex, social context in which social touch occurs, and specific body areas being touched. In our study, adult participants reported how pleasant, erogenous and appropriate they would consider touches delivered by another person over their entire body in intimate (date), friendly (dance class) and professional (physiotherapy-massage session) social contexts. Autistic adults reported social touch to be less pleasant, erogenous and appropriate specifically in intimate and friendly social contexts and in body areas typically touched in these situations. Importantly, autistic females seem more at risk to experience unpleasant social touch as, although they considered it more unpleasant than non-autistic females and autistic males, they did consider it similarly appropriate in professional social contexts where touch is normed to be socially appropriate.Implications for practice, research or policyOur results might improve awareness and understanding about autistic adults' different, and often more discomforting, experience of social touch and thus help consider and respect it during everyday social interactions. Our results might also benefit future research investigating, for instance, the neural underpinnings of social touch differences in autism or aiming at developing support for autistic individuals seeking help in the diverse spheres of social touch.

Granger Geweke Causality reveals information exchange during physical interaction is modulated by task difficulty

The haptic sense is an important mode of communication during physical interactions, and it is known to enable humans to estimate key features of their partner's behavior. It is proposed that such estimations are based upon the exchange of information mediated by the interaction forces, resulting in role distribution and coordination between partners. In the present study, we examined whether the information exchange is functionally modified to adapt to the task, or whether it is a fixed process, leaving the adaptation to individual's behaviors. We analyzed the forces during an empirical dyadic interaction task using Granger-Geweke causality analysis, which allowed us to quantify the causal influence of each individual's forces on their partner's. The dynamics of relative phase were also examined. We observed an increase of inter-partner influence with an increase in the spatial accuracy required by the task, demonstrating an adaptation of information flow to the task. This increase of exchange with the spatial accuracy constraint was accompanied by an increase of errors and of the variability of the relative phase between forces. The influence was dominated by participants in a specific role, showing a clear role division as well as task division between the dyad partners. Moreover, the influence occurred in the [2.15-7] Hz frequency band, demonstrating its importance as a frequency band of interest during cooperation involving haptic interaction. Several interpretations are introduced, ranging from sub-division of motion control to phase-amplitude coupling.

Attitudes to Interpersonal Touch in the Workplace in Autistic and non-Autistic Groups

Unemployment and underemployment have consistently been shown to be higher in autistic adults relative to non-autistic adults. This may be due, in part, to a lack of workplace accommodations being made for autistic people. One factor that may contribute to employment inequalities in autistic people is differences in attitudes towards interpersonal touch. This study acts as a preliminary investigation into whether employed autistic and non-autistic participants differ in their attitudes towards touch in the workplace, and in their loneliness and wellbeing. The current dataset was drawn from a larger online survey (the Touch Test) designed to explore attitudes and experiences towards touch. We found that employed autistic participants had more negative attitudes to general, social and workplace touch relative to non-autistic participants. Autistic participants also experienced greater loneliness and reduced wellbeing. Attachment-related anxiety was the only significant predictor of wellbeing in employed autistic adults. However, attachment-related anxiety, general attitudes to touch and the role of touch in the workplace predicted wellbeing in employed non-autistic adults. With regards to loneliness, general attitudes to touch and the role of touch in the workplace predicted loneliness in autistic participants. We also replicated the finding that a greater proportion of autistic participants were unemployed relative to non-autistic participants. Collectively, this research highlights the importance of considering touch in research investigating employment, and its impact on loneliness and wellbeing, in autistic participants.

A Shared Intentionality Account of Uniquely Human Social Bonding

Many mechanisms of social bonding are common to all primates, but humans seemingly have developed some that are unique to the species. These involve various kinds of interactive experiences-from taking a walk together to having a conversation-whose common feature is the triadic sharing of experience. Current theories of social bonding have no explanation for why humans should have these unique bonding mechanisms. Here we propose a shared intentionality account of uniquely human social bonding. Humans evolved to participate with others in unique forms of cooperative and communicative activities that both depend on and create shared experience. Sharing experience in these activities causes partners to feel closer because it allows them to assess their partner's cooperative competence and motivation toward them and because the shared representations created during such interactions make subsequent cooperative interactions easier and more effective.

Enhancing the design of wine labels

Introduction

The knowledge accrued through research in the domain of crossmodal correspondences has had a significant influence on a diverse array of disciplines, including behavioral studies, neuroscience, computational modeling, and notably, marketing, with the objective of aligning sensory experiences to help shape patterns of consumer behavior. A study is reported that explores the extension of these principles to the communication of products having a notably complex sensory profile, specifically within the context of wine. The central aim of the project is to explore the feasibility of using crossmodal communication as a strategic tool to augment the congruence between the consumers' multisensory expectations and their sensory experiences. For consumers venturing into the realm of wine selection without the advantage of prior tasting experience, it is of paramount importance to possess a robust understanding of the mandated information. This encompasses critical elements such as the wine's origin, grape varietal(s) used, geographical indications, producer qualifications, and the potential implications of these factors on the final wine product. This level of comprehension stands as a necessary prerequisite, enabling these consumers to make informed choices that align with their preferences, even in the absence of previous sensory encounters. Nonetheless, semiotic investigations underscore the significance attributed to symbolic components such as signs, logos, colors, gestures, and linguistic cues. Research from the field performing multisensory studies, presents a counterpoint to prevailing communication paradigms, advocating for a heightened incorporation of metaphors, analogies, symbols, metonymies, and allegories. This alternative approach aims to enhance the efficacy of communication strategies, offering a more profound and evocative means of conveying intricate messages on a more holistic level.

Methods

A questionnaire was sent to a specific group of engaged wine consumers (n = 329). Besides questions regarding demographics, purchase behavior, and consumption behavior, the questionnaire included examples of multisensory communication through a selection of symbols, as well as alternative wine information.

Results

The results showed significant correlations between demographics, consumption behavior, and attitudes toward the tested multisensory symbols and alternative information, thus helping to gain a better understanding of the sensory properties that should be communicated on wine labels.

Discussion

The findings reported here highlight the effectiveness of visual crossmodal communication as a promising pathway capable of skillfully capturing consumer attributes, conveying multisensory experiences, and portraying the comprehensive timeline of taste evolution. As a result, it assumes a pivotal role as a communicative tool for intricate consumables, like wine, functioning at the crossroads of visual and sensory dimensions.

Hedonic and autonomic responses in promoting affective touch

Interpersonal touch is intrinsically reciprocal since it entails a person promoting and another receiving the touch. While several studies have investigated the beneficial effects of receiving affective touch, the affective experience of caressing another individual remains largely unknown. Here, we investigated the hedonic and autonomic responses (skin conductance and heart rate) in the person promoting affective touch. We also examined whether interpersonal relationship, gender, and eye contact modulate these responses. As expected, caressing the partner was perceived as more pleasant than caressing a stranger, especially if the affective touch occurred together with mutual eye contact. Promoting affective touch to the partner also resulted in a decrease of both autonomic responses and anxiety levels, suggesting the occurrence of a calming effect. Additionally, these effects were more pronounced in females compared to males, indicating that hedonic and autonomic aspects of affective touch are modulated by both social relationship and gender. These findings show for the first time that caressing a beloved one is not only pleasant but also reduces autonomic responses and anxiety in the person promoting the touch. This might suggest that affective touch has an instrumental role for romantic partners in promoting and reinforcing their affective bonding.

Social and Emotional Touch Between Romantic Partners is Affectively More Pleasant Due to Finely Tuned Contact Interactions

Our daily observations tell us that the delivery of social sentiments and emotions differs between strangers and romantic partners. This work explores how relationship status influences our delivery and perception of social touches and emotions, by evaluating the physics of contact interactions. In a study with human participants, strangers and romantically involved touchers delivered emotional messages to receivers' forearms. Physical contact interactions were measured using a customized 3D tracking system. The results indicate that strangers and romantic receivers recognize emotional messages with similar accuracy, but with higher levels of valence and arousal between romantic partners. Further investigation into the contact interactions which underlie the higher levels of valence and arousal reveals that a toucher tunes their strategy with their romantic partner. For example, when stroking, romantic touchers use velocities preferential to C-tactile afferents, and maintain contact for longer durations with larger contact areas. Notwithstanding, while we show that relationship intimacy influences the deployment of touch strategies, such impact is relatively subtle compared to distinctions between gestures, emotional messages, and individual preferences.

Perspectives on interpersonal touch are related to subjective sleep quality

Affective touch has been reported for its calming effects; however, it is less clear whether touch is associated with sleep. Here, the relationship between different touch variables and self-reported sleep indicators was investigated. Data were extracted from the Touch Test, a cross-sectional survey conducted in 2020. Data from a sample of 15,049 healthy adults from the UK (mean age = 56.13, SD = 13.8; 75.4% female) were analysed. Participants were asked to attribute positive, negative, or no effects on sleep to hugs, strokes, massages, intimate touch, and sleep onset with and without touch. The time since last intentional touch, touch amount satisfaction, and childhood bed routine with hugs and kisses were assessed. Sleep quality, duration, latency, wake after sleep onset and diurnal preference were measured. Data were analysed using chi-square tests and logistic regressions. Affective touch before sleep was perceived to have positive effects on sleep. Touch recency emerged as a significant predictor for some sleep variables, with a longer timespan since the last intentional touch relating to improved sleep quality, longer sleep duration, and shorter and fewer instances of waking up after sleep onset in some participants. Experiencing too much touch was related to lower sleep quality and higher instances of waking up after sleep onset. These findings highlight the importance of interpersonal touch for subjective sleep quality.

The Dark Side of Interpersonal Touch: Physical Contact Leads to More Non-compliance With Preventive Measures to COVID-19

Following preventive measures is crucial for slowing the rate of COVID-19 spread. To date, most research has focused on the role of individual differences and personality in compliance with preventive measures to COVID-19. Building on findings that interpersonal touch instills a feeling of security, we propose that interpersonal touching behavior, an underexplored factor tied to social interaction, leads to more breaches of coronavirus restrictions by inducing security feelings. In a lab experiment (Experiment 1) and a field study (Experiment 2), we demonstrated that a female experimenter's fleeting and comforting pat on the shoulder made people less willing to abide by preventive measures in their self-report and actual behavior. Further, we excluded a potential alternative explanation that touch intervention by the experimenter presents the defiance of COVID-19 rules because the effect cannot be observed when the touch consists of a handshake rather than a comforting pat on the shoulder (Experiment 3). Finally, consistent with our theoretical perspective, the results revealed that sense of security mediated the effect of interpersonal touch on violation of instructions to follow coronavirus precautions. Taken together, interpersonal touch not only enhances trust and security, but also can push people away from health guidelines.

Touched by your words: How touch-related vocabulary prompts charitable behavior by reducing the negative effect of disgust

Getting help is often difficult for people who trigger disgust (e.g., homeless, sick, or disabled people) as well as the charities representing them because of low trust in these groups. Prior research has demonstrated that physical contact can help increase generosity. However, it is difficult to trigger this phenomenon-called Midas Touch Effect-when people feel disgust and are uncomfortable with interpersonal touch. This research examines touch-related vocabulary (e.g., "I would be touched," "anyone who I can contact") as an alternative, non-physical way for prompting the Midas Touch Effect. This research examines if such a vocabulary may reduce the negative effects of disgust on trust, and thus increase the willingness to donate. Across two studies, it is shown that while disgust has a negative effect on trust and willingness to donate to a homeless person when no touch-related vocabulary is used, no such negative effect is observed when the message includes touch-related vocabulary.

The Associations Between Attitudes Toward Interpersonal Affective Touch, Negative Cognitions and Social Anxiety: A Pilot Study

Objective: Affectionate touch promotes psychological well-being likely through inducing cognitive and neurobiological changes, which implies the inverse association of affectionate touch to negative cognitive and psychosocial outcomes. Our aim was to explore relationships between attitudes toward interpersonal touch and social anxiety through fear of negative evaluation and self-critical rumination as mediating variables.Method: Data from 250 participants (69.6% females, n = 174) ranging in age from 18 to 65 years were collected through self-report inventories assessing attitudes toward physical touch from friends and family, nonromantic intimate person and unfamiliar person, fear of negative evaluation, self-critical rumination, and social anxiety. A moderated-mediation analysis was conducted. Results: No direct link was seen between attitudes toward friends and family touch experiences and social anxiety in both genders, but mediation through fear of negative evaluation was significant (p < .05). Attitudes toward nonromantic intimate touch were related to social anxiety only in females and only indirectly through self-critical rumination (p < .05). In both males and females, attitudes toward touch from unfamiliar persons were linked to social anxiety directly (p < .05) but indirect paths through fear of negative evaluation (p < .05) and self-critical rumination were seen only in females (p < .05). Conclusions: Findings indicate that attitudes toward interpersonal affectionate touch may be predictive of social anxiety and the negative cognitions associated with it, extending previous findings on social pain and attesting to the potential clinical utility of touch-based interventions for social anxiety.

Complexity theory in the management of patients with musculoskeletal pain

Nonlinear systems are not susceptible to research with a reductionist approach. In this sense, the complexity theory provides an alternative approach to quantify the importance of contextual factors in patients with musculoskeletal pain. The use of positive (placebo) or negative (nocebo) contextual factors in the therapeutic setting could largely account for the non-specific component of treatment efficacy, directly affecting the quality of patients’ health-related outcomes (e.g., pain, disability, or satisfaction). In recent years, there has been a better understanding of the effects of contextual factors. However, the knowledge and awareness of them is limited and heterogeneous among physical therapists, reducing their translational value in the field of physiotherapy. The purpose of this essay is to describe the management of patients with musculoskeletal pain from the complexity theory perspective.

The brain-body disconnect: A somatic sensory basis for trauma-related disorders

Although the manifestation of trauma in the body is a phenomenon well-endorsed by clinicians and traumatized individuals, the neurobiological underpinnings of this manifestation remain unclear. The notion of somatic sensory processing, which encompasses vestibular and somatosensory processing and relates to the sensory systems concerned with how the physical body exists in and relates to physical space, is introduced as a major contributor to overall regulatory, social-emotional, and self-referential functioning. From a phylogenetically and ontogenetically informed perspective, trauma-related symptomology is conceptualized to be grounded in brainstem-level somatic sensory processing dysfunction and its cascading influences on physiological arousal modulation, affect regulation, and higher-order capacities. Lastly, we introduce a novel hierarchical model bridging somatic sensory processes with limbic and neocortical mechanisms regulating an individual's emotional experience and sense of a relational, agentive self. This model provides a working framework for the neurobiologically informed assessment and treatment of trauma-related conditions from a somatic sensory processing perspective.

Pet ownership, feelings of loneliness, and mood in people affected by the first COVID-19 lockdown

The outbreak of the COVID-19 pandemic has caused dramatic changes to our lifestyle, particularly affecting our ability to interact “in person” with our social network. These changes have had a detrimental effect on the mental welfare of the global population. The international questionnaire “Pets in Lockdown” was designed to investigate whether feelings of loneliness were affecting the mood of people during the COVID-19 lockdown and whether pet ownership may have had a positive influence on both loneliness and general mood. As expected, higher loneliness scores were associated with higher negative and lower positive affective states. In addition, lower loneliness scores were associated with pet ownership and living with other people, but not with more frequent interactions with people from outside the household, suggesting that physical and close contact has an important role in decreasing feelings of loneliness. Besides the effects on the loneliness score, pet ownership was not associated with positive or negative affective states. The strength of the attachment to animals, measured as the amount of comfort that people obtain from their pets, was stronger in people with potentially limited access to affiliative physical human contact and was associated with both higher positive and negative affective states. Additionally, people obtained significantly more comfort from dogs and horses compared with other pet species. The results suggest that during the confinement period, pets may have benefited people with smaller social networks by alleviating loneliness and offering comfort and embodied close contact.

Interacting humans use forces in specific frequencies to exchange information by touch

Object-mediated joint action is believed to be enabled by implicit information exchange between interacting individuals using subtle haptic signals within their interaction forces. The characteristics of these haptic signals have, however, remained unclear. Here we analyzed the interaction forces during an empirical dyadic interaction task using Granger–Geweke causality analysis, which allowed us to quantify the causal influence of each individual’s forces on their partner’s. We observed that the inter-partner influence was not the same at every frequency. Specifically, in the frequency band of [2.15–7] Hz, we observed inter-partner differences of causal influence that were invariant of the movement frequencies in the task and present only when information exchange was indispensable for task performance. Moreover, the inter-partner difference in this frequency band was observed to be correlated with the task performance by the dyad. Our results suggest that forces in the [2.15–7] Hz band constitute task related information exchange between individuals during physical interactions.

The analgesic power of pleasant touch in individuals with chronic pain: Recent findings and new insights

This mini-review covers recent works on the study of pleasant touch in patients with chronic pain (CP) and its potential use as a treatment. While experiments have demonstrated that pleasant touch, through the activation of CT-afferents and the brain regions involved in its affective value, might reduce the unpleasantness and intensity of induced pain, the interaction between pleasant touch and CP remains under-examined. Some experiments show that CP might disrupt the positive aspects of receiving pleasant touch, while in other studies the perception of pleasantness is preserved. Moreover, only a few attempts have been made to test whether touch can have a modulatory effect on CP, but these results also remain inconclusive. Indeed, while one recent study demonstrated that CT-touch can diminish CP after a short stimulation, another study suggested that pleasant touch might not be sufficient. Future studies should further investigate the psychological and neural interplay between pleasant touch and CP. In the conclusion of this mini-review, we propose a new tool we have recently developed using immersive virtual reality (IVR).

In touch: Cardiac and respiratory patterns synchronize during ensemble singing with physical contact

Musical ensemble performances provide an ideal environment to gain knowledge about complex human interactions. Network structures of synchronization can reflect specific roles of individual performers on the one hand and a higher level of organization of all performers as a superordinate system on the other. This study builds on research on joint singing, using hyperscanning of respiration and heart rate variability (HRV) from eight professional singers. Singers performed polyphonic music, distributing their breathing within the same voice and singing without and with physical contact: that is touching each other's shoulder or waist. The idea of singing with touch was motivated by historical depictions of ensemble performances that showed singers touching each other. It raises the question of the potential benefit of touch for group performances. From a psycho-physiological point of view, physical contact should increase the synchronization of singing coordination. The results confirm previous findings on synchronization of respiration and HRV during choir singing and extend those findings to a non-homophonic musical repertoire while also revealing an increase in synchronization in respiration during physical contact. These effects were significant across different frequency ranges. The effect of physical contact was stronger when all singers were singing in comparison to the partial ensemble. Importantly, the synchronization could not be fully explained by the singing action (i.e., singing the same voice, or singing vs. listening) or by the standing position or touch. This finding suggests a higher level of organization of all singers, forming a superordinate system.

Exploring views on affective haptic devices in times of COVID-19

Affective haptic devices (AHDs) are communication technologies utilizing the sense of touch, and include mediated social touch (MST), symbolic haptic messaging, and awareness systems that, for example, let one feel another person's heartbeat. The COVID-19 pandemic and consequent social distancing measures have led to a reemphasis of the importance of social touch, and many people have experienced firsthand what it is like to miss touching loved ones. This offers an excellent opportunity to study people's intention to use AHDs. For this purpose, a survey study (n = 277) was conducted combining qualitative and quantitative data analysis methods. Touch deprivation, resulting from not being able to touch a loved one, was associated with intention to use AHDs: the more deprived an individual, the higher his or her intention to use AHDs. Technology readiness and touch aversion did not affect intention to use AHDs. AHDs for symbolic messaging gained higher interest than MST and awareness devices, and long-distance relationships were seen as the most likely scenario for using AHDs. Bi-directionality, synchronicity, and symmetry were regarded as important features for providing shared meaning and a sense of connectedness. Reviewability, multimodality, and actuation type were also deemed important. Limitations of the study and implications for the design of AHDs are discussed.

Inviting Robot Touch (By Design)

What is the role of touch in inviting social interaction with robots? Forms of functional haptics in collaboration and socially assistive robots for example indicate one pathway. But what of more naturalistic and affective forms of touch that are more inviting, that encourage pro-social behaviors? This is a tale of three loops. First, the haptic feedback loop, where human-human touch still remains underexplored, and where human-machine touch is produced through mechanical engineering as ‘force display’ and perceived by the user as tactile (e.g. Srinivasan and Basdogan 1997). Second, the affective feedback loop, courtesy of Höök (2008; 2009) and Dumouchel and Damiano (2017), where technical systems influence, and are influenced by, a human user corporeally. Bringing these loops together encourages interaction design to consider how touch and affect may more effectively invite a range of users to interact with social robots, and their role in the perception of Artificial Empathy (AE).

Mirror neurons 30 years later: implications and applications

Mirror neurons (MNs) were first described in a seminal paper in 1992 as a class of monkey premotor cells discharging during both action execution and observation. Despite their debated origin and function, recent studies in several species, from birds to humans, revealed that beyond MNs properly so called, a variety of cell types distributed among multiple motor, sensory, and emotional brain areas form a 'mirror mechanism' more complex and flexible than originally thought, which has an evolutionarily conserved role in social interaction. Here, we trace the current limits and envisage the future trends of this discovery, showing that it inspired translational research and the development of new neurorehabilitation approaches, and constitutes a point of no return in social and affective neuroscience.

What Makes Touch Comfortable? An Examination of Touch Giving and Receiving in Two Cultures

This study examined how touch role and culture shape affective touch experiences. Germans (N = 130) and Chinese (N = 130) were surveyed once as toucher and once as touchee. For different touch actions, they (a) provided free-text descriptions of what prompts touch, (b) indicated with whom touch feels comfortable, and (c) highlighted areas of touch comfort on a body outline. Overall, touch was prompted by affectionate feelings, was more comfortable with more closely bonded individuals, and when directed at the upper arms, shoulders, and upper back. Touch role mattered for the experiences prompting touch in that touchees felt less positive than touchers. Culture differentiated touch comfort topographies. Compared with Chinese, Germans felt more comfortable with more intimate touch to the torso and upper back and less comfortable with more public touch to the hands. Notably, however, examining touch role and culture revealed more overlap than divergence, ensuring mutual comfort as individuals physically connect.

3D Visual Tracking to Quantify Physical Contact Interactions in Human-to-Human Touch

Across a plethora of social situations, we touch others in natural and intuitive ways to share thoughts and emotions, such as tapping to get one’s attention or caressing to soothe one’s anxiety. A deeper understanding of these human-to-human interactions will require, in part, the precise measurement of skin-to-skin physical contact. Among prior efforts, each measurement approach exhibits certain constraints, e.g., motion trackers do not capture the precise shape of skin surfaces, while pressure sensors impede skin-to-skin contact. In contrast, this work develops an interference-free 3D visual tracking system using a depth camera to measure the contact attributes between the bare hand of a toucher and the forearm of a receiver. The toucher’s hand is tracked as a posed and positioned mesh by fitting a hand model to detected 3D hand joints, whereas a receiver’s forearm is extracted as a 3D surface updated upon repeated skin contact. Based on a contact model involving point clouds, the spatiotemporal changes of hand-to-forearm contact are decomposed as six, high-resolution, time-series contact attributes, i.e., contact area, indentation depth, absolute velocity, and three orthogonal velocity components, together with contact duration. To examine the system’s capabilities and limitations, two types of experiments were performed. First, to evaluate its ability to discern human touches, one person delivered cued social messages, e.g., happiness, anger, sympathy, to another person using their preferred gestures. The results indicated that messages and gestures, as well as the identities of the touchers, were readily discerned from their contact attributes. Second, the system’s spatiotemporal accuracy was validated against measurements from independent devices, including an electromagnetic motion tracker, sensorized pressure mat, and laser displacement sensor. While validated here in the context of social communication, this system is extendable to human touch interactions such as maternal care of infants and massage therapy.

Linking Haptic Parameters to the Emotional Space for Mediated Social Touch

Social touch is essential for creating and maintaining strong interpersonal bonds amongst humans. However, when distance separates users, they often rely on voice and video communication technologies to stay connected with each other, and the lack of tactile interactions between users lowers the quality of the social interactions. In this research, we investigated haptic patterns to communicate five tactile messages comprising of four types of social touch (high five, handshake, caress, and asking for attention) and one physiological signal (the pulse of a heartbeat), delivered on the hand through a haptic glove. Since social interactions are highly dependent on their context, we conceived two interaction scenarios for each of the five tactile messages, conveying distinct emotions being spread across the circumplex model of emotions. We conducted two user studies: in the first one participants tuned the parameters of haptic patterns to convey tactile messages in each scenario, and a follow up study tested naïve participants to assess the validity of these patterns. Our results show that all haptic patterns were recognized above chance level, and the well-defined parameter clusters had a higher recognition rate, reinforcing the hypothesis that some social touches have more universal patterns than others. We also observed parallels between the parameters' levels and the type of emotions they conveyed based on their mapping in the circumplex model of emotions.

What Can a Robot’s Skin Be? Designing Texture-Changing Skin for Human-Robot Social Interaction

Biological skin has numerous functions like protection, sensing, expression, and regulation. On the contrary, a robot’s skin is usually regarded as a passive and static separation between the body and environment. In this paper, we explore the design opportunities of a robot’s skin as a socially expressive medium. Inspired by living organisms, we discuss the roles of interactive robotic skin from four perspectives: expression, perception, regulation, and mechanical action. We focus on the expressive function of skin to sketch design concepts and present a flexible technical method for embodiment. The proposed method integrates pneumatically actuated dynamic textures on soft skin, with forms and kinematic patterns generating a variety of visual and haptic expressions. We demonstrate the proposed design space with six texture-changing skin prototypes and discuss their expressive capacities.

Visuo-Motor Affective Interplay: Bonding Scenes Promote Implicit Motor Pre-dispositions Associated With Social Grooming-A Pilot Study

Proximity and interpersonal contact are prominent components of social connection. Giving affective touch to others is fundamental for human bonding. This brief report presents preliminary results from a pilot study. It explores if exposure to bonding scenes impacts the activity of specific muscles related to physical interaction. Fingers flexion is a very important component when performing most actions of affectionate contact. We explored the visuo-motor affective interplay by priming participants with bonding scenes and assessing the electromyographic activity of the fingers flexor muscle, in the absence of any overt movements. Photographs of dyads in social interaction and of the same dyads not interacting were employed. We examined the effects upon the electromyographical activity: (i) during the passive exposure to pictures, and (ii) during picture offset and when expecting the signal to perform a fingers flexion task. Interacting dyads compared to matched non-interacting dyads increased electromyographic activity of the fingers flexor muscle in both contexts. Specific capture of visual bonding cues at the level of visual cortex had been described in the literature. Here we showed that the neural processing of visual bonding cues reaches the fingers flexor muscle. Besides, previous visualization of bonding cues enhanced background electromyographic activity during motor preparation to perform the fingers flexion task, which might reflect a sustained leakage of central motor activity downstream leading to increase in firing of the respective motor neurons. These data suggest, at the effector level, an implicit visuo-motor connection in which social interaction cues evoke intrinsic dispositions toward affectionate social behavior.

Robotic Stroking on the Face and Forearm: Touch Satiety and Effects on Mechanical Pain

Background: Slow stroking touch is generally perceived as pleasant and reduces thermal pain. However, the tactile stimuli applied tend to be short-lasting and typically applied to the forearm. This study aimed to compare the effects of a long-lasting brushing stimulus applied to the facial region and the forearm on pressure pain thresholds (PPTs) taken on the hand. Outcome measurements were touch satiety and concurrent mechanical pain thresholds of the hand.

Methods: A total of 24 participants were recruited and randomized to receive continuous stroking, utilizing a robotic stimulator, at C-tactile (CT) favorable (3 cm/s) and non-favorable (30 cm/s) velocities applied to the right face or forearm. Ratings of touch pleasantness and unpleasantness and PPTs from the hypothenar muscle of the right hand were collected at the start of stroking and once per minute for 5 min.

Results: A reduction in PPTs (increased pain sensitivity) was observed over time (P < 0.001). However, the increase in pain sensitivity was less prominent when the face was stroked compared to the forearm (P = 0.001). Continuous stroking resulted in a significant interaction between region and time (P = 0.008) on pleasantness ratings, with a decline in ratings observed over time for the forearm, but not on the face. Unpleasantness ratings were generally low.

Conclusion: We observed touch satiety for 5 min of continuous robotic brushing on the forearm confirming previous studies. However, we did not observe any touch satiety for brushing the face. Mechanical pain sensitivity, measured in the hand, increased over the 5-min period but less so when paired with brushing on the face than with brushing on the forearm. The differential effects of brushing on the face and forearm on touch satiety and pain modulation may be by the differences in the emotional relevance and neuronal pathways involved.

Physical Intimacy in Older Couples' Everyday Lives: Its Frequency and Links with Affect and Salivary Cortisol

OBJECTIVES

Physical intimacy is important for communicating affection in romantic relationships. Theoretical and empirical work highlights linkages between physical intimacy, affect, and physiological stress among young and middle-aged adults, but not older adults. We examine physical intimacy and its associations with positive and negative affect and cortisol levels in the daily lives of older couples.

METHOD

We applied actor-partner multilevel models to repeated daily life assessments of physical intimacy (experienced and wished) and affect obtained six times a day over seven consecutive days from 120 older heterosexual German couples (Mage= 71.6, SDage= 5.94). Physiological stress was indexed as total daily cortisol output, the area under the curve with respect to ground (AUCg).

RESULTS

Physical intimacy experienced and wished were reported at the vast majority of occasions, but to different degrees at different times. Within persons, in moments when participants experienced more physical intimacy, older women reported less negative affect, whereas older men reported more positive affect. Between persons, higher overall levels of physical intimacy experienced were associated with higher positive affect and less negative affect among women and with lower daily cortisol output among men. A stronger wish for intimacy was related to more negative affect among both women and men, and to higher daily cortisol output among men.

DISCUSSION

Physical intimacy is linked with mood and stress hormones in the daily life of older couples. We consider routes for future inquiry on physical intimacy among older adults.

Therapeutic Alliance as Active Inference: The Role of Therapeutic Touch and Synchrony

Recognizing and aligning individuals' unique adaptive beliefs or "priors" through cooperative communication is critical to establishing a therapeutic relationship and alliance. Using active inference, we present an empirical integrative account of the biobehavioral mechanisms that underwrite therapeutic relationships. A significant mode of establishing cooperative alliances-and potential synchrony relationships-is through ostensive cues generated by repetitive coupling during dynamic touch. Established models speak to the unique role of affectionate touch in developing communication, interpersonal interactions, and a wide variety of therapeutic benefits for patients of all ages; both neurophysiologically and behaviorally. The purpose of this article is to argue for the importance of therapeutic touch in establishing a therapeutic alliance and, ultimately, synchrony between practitioner and patient. We briefly overview the importance and role of therapeutic alliance in prosocial and clinical interactions. We then discuss how cooperative communication and mental state alignment-in intentional communication-are accomplished using active inference. We argue that alignment through active inference facilitates synchrony and communication. The ensuing account is extended to include the role of (C-) tactile afferents in realizing the beneficial effect of therapeutic synchrony. We conclude by proposing a method for synchronizing the effects of touch using the concept of active inference.

Imaging affective and non-affective touch processing in two-year-old children

Touch is an important component of early parent-child interaction and plays a critical role in the socio-emotional development of children. However, there are limited studies on touch processing amongst children in the age range from one to three years. The present study used frequency-domain diffuse optical tomography (DOT) to investigate the processing of affective and non-affective touch over left frontotemporal brain areas contralateral to the stimulated forearm in two-year-old children. Affective touch was administered by a single stroke with a soft brush over the child's right dorsal forearm at 3 cm/s, while non-affective touch was provided by multiple brush strokes at 30 cm/s. We found that in the insula, the total haemoglobin (HbT) response to slow brushing was significantly greater than the response to fast brushing (slow > fast). Additionally, a region in the postcentral gyrus, Rolandic operculum and superior temporal gyrus exhibited greater response to fast brushing than slow brushing (fast > slow). These findings confirm that an adult-like pattern of haemodynamic responses to affective and non-affective touch can be recorded in two-year-old subjects using DOT. To improve the accuracy of modelling light transport in the two-year-old subjects, we used a published age-appropriate atlas and deformed it to match the exterior shape of each subject's head. We estimated the combined scalp and skull, and grey matter (GM) optical properties by fitting simulated data to calibrated and coupling error corrected phase and amplitude measurements. By utilizing a two-compartment cerebrospinal fluid (CSF) model, the accuracy of estimation of GM optical properties and the localization of activation in the insula was improved. The techniques presented in this paper can be used to study neural development of children at different ages and illustrate that the technology is well-tolerated by most two-year-old children and not excessively sensitive to subject movement. The study points the way towards exciting possibilities in functional imaging of deeper functional areas near sulci in small children.

Newborns' clinical conditions are correlated with the neonatal assessment manual scorE (NAME)

OBJECTIVE

To investigate the relationship between the Neonatal Assessment Manual scorE (NAME) and newborns' clinical condition on a large number of infants. The NAME model was developed as an instrument to assess the infant's general conditions, especially in NICUs, by evaluating how the infant's body responds to an external stressor such as static touch. Previous studies, employing experienced assessors, showed good validity indices as well as high inter-rater reliability.

STUDY DESIGN

Newborns were recruited at the "Vittore Buzzi" Pediatric Hospital NICU ward in Milan and their clinical conditions were collected through a standardized form-the complexity index. Two manual practitioners assessed all eligible newborns using the NAME scores. Data was analyzed using Kendall's τ correlation and odds ratio (OR) to assess the relationship between the NAME scores and the complexity index.

RESULTS

Two hundred two newborns (46% female; 34.1 w ± 4.3; birth weight of 2,093.4 gr ± 879.8) entered the study. The Kendall's correlation between the clinical conditions (complexity index) and the NAME score was -0.206 [95% CI: (-0.292, -0.116), p-value < 0.001], corresponding to an OR of 0.838 [95% CI: (0.757, 0.924), p-value < 0.001]. Further exploratory analyses showed significant correlation between gestational age, birth weight and NAME scores.

CONCLUSION

The present paper adds evidence to the NAME model validity by demonstrating its applicability in the clinical neonatological context.

Acute tryptophan depletion alters affective touch perception

RATIONALE

Affiliative tactile interactions help regulate physiological arousal and confer resilience to acute and chronic stress. C-tactile afferents (CTs) are a population of unmyelinated, low threshold mechanosensitive cutaneous nerve fibres which respond optimally to a low force stimulus, moving at between 1 and 10 cm/s. As CT firing frequencies correlate positively with subjective ratings of touch pleasantness, they are hypothesised to form the first stage of encoding affiliative tactile interactions. Serotonin is a key modulator of social responses with known effects on bonding.

OBJECTIVES

The aim of the present study was to determine the effect of acutely lowering central serotonin levels on perceptions of CT-targeted affective touch.

METHODS

In a double blind, placebo-controlled design, the effect of acute tryptophan depletion (ATD) on 25 female participants' ratings of directly and vicariously experienced touch was investigated. Psychophysical techniques were used to deliver dynamic tactile stimuli; some velocities were targeted to optimally activate CTs (1-10 cm/s), whereas other, faster and slower strokes fell outside the CT optimal range. Discriminative tactile function, cold pain threshold and tolerance were also measured.

RESULTS

ATD significantly increased pleasantness ratings of both directly and vicariously experienced affective touch, increasing discrimination of the specific hedonic value of CT targeted velocities. While ATD had no effect on either tactile or cold pain thresholds, there was a trend for reduced tolerance to cold pain.

CONCLUSIONS

These findings are consistent with previous reports that depletion of central serotonin levels modulates neural and behavioural responsiveness to appetitive sensory signals.