Across a plethora of social situations, we touch others in natural and intuitive ways to share thoughts and emotions, such as tapping to get ones attention or caressing to soothe ones 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 touchers hand is tracked as a posed and positioned mesh by fitting a hand model to detected 3D hand joints, whereas a receivers 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 systems 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 systems 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.

The main objective of this study is to investigate whether one can use recordings of human-to-human touch, such as a caress, to improve tactile apparent motion interfaces to make them feel more natural. We report here preliminary recordings of natural and continuous human-to-human caresses. To do this, six accelerometers were positioned on the receiving hand next to the stimulated area while a finger gently stroked the skin. The results suggest that we are able to capture signals from real human caresses that can be compared to signals produced by apparent motion stimuli. This is encouraging for our plan to continue the study in the second stage, which consists of tuning vibrotactile actuators to reproduce a similar pattern of vibrational responses in the accelerometers. In this way, the actuators mimic human behavior.

Neural mechanisms of touch are typically studied in laboratory settings using robotic or other types of well-controlled devices. Such stimuli are very different from highly complex naturalistic human-to-human touch interactions. The lack of scientifically useful naturalistic stimuli hampers progress, particularly in social touch research. Vision science, on the other hand, has benefitted from inventions such as virtual reality systems that have provided researchers with precision control of naturalistic stimuli. In the field of touch research, producing and manipulating stimuli is particularly challenging due to the complexity of skin mechanics. Here, we review the history of touch neuroscience focusing on the contrast between strictly controlled and naturalistic stimuli, and compare the field to vision science. We discuss new methods that may overcome obstacles with precision-controlled tactile stimuli, and recent successes in naturalistic texture production. In social touch research, precise tracking and measurement of naturalistic human-to-human touch interactions offer exciting new possibilities.

Middleton, Perini et al. show that the role of Na(v)1.7 extends beyond pain perception. Using a multidisciplinary, cross-species approach, they show that Na(v)1.7 is also essential for C-low threshold mechanoreceptor function in mice and humans, regulating pleasant touch, punctate discrimination and sensitivity to cooling. Patients with bi-allelic loss of function mutations in the voltage-gated sodium channel Nav1.7 present with congenital insensitivity to pain (CIP), whilst low threshold mechanosensation is reportedly normal. Using psychophysics (n = 6 CIP participants and n = 86 healthy controls) and facial electromyography (n = 3 CIP participants and n = 8 healthy controls), we found that these patients also have abnormalities in the encoding of affective touch, which is mediated by the specialized afferents C-low threshold mechanoreceptors (C-LTMRs). In the mouse, we found that C-LTMRs express high levels of Nav1.7. Genetic loss or selective pharmacological inhibition of Nav1.7 in C-LTMRs resulted in a significant reduction in the total sodium current density, an increased mechanical threshold and reduced sensitivity to non-noxious cooling. The behavioural consequence of loss of Nav1.7 in C-LTMRs in mice was an elevation in the von Frey mechanical threshold and less sensitivity to cooling on a thermal gradient. Nav1.7 is therefore not only essential for normal pain perception but also for normal C-LTMR function, cool sensitivity and affective touch.

We routinely communicate distinct social and emotional sentiments through nuanced touch. For example, we might gently hold anothers arm to offer a sense of calm, yet intensively hold anothers arm to express excitement or anxiety. As this example indicates, distinct sentiments may be shaped by the subtlety in ones touch delivery. This work investigates how slight distinctions in skin-to-skin contact influence both the recognition of cued emotional messages (e.g., anger, sympathy) and the rating of emotional content (i.e., arousal, valence). By self-selecting preferred gestures (e.g., holding, stroking), touchers convey distinct messages by touching the receivers forearm. Skin-to-skin contact attributes (e.g., velocity, depth, area) are optically tracked in high resolution. Contact is then examined within gesture, between messages. The results indicate touchers subtly, but significantly, vary contact attributes of a gesture to communicate distinct messages, which are recognizable by receivers. This tuning also correlates with receivers arousal and valence. For instance, arousal increases with velocity for stroking, and depth for holding. Moreover, as shown here with human-to-human touch, valence is tied with velocity, which is the same trend as reported with brushes. The findings indicate that subtle nuance in skin-to-skin contact is important in conveying social messages and inducing emotions.

Touch is a powerful communication tool, but we have a limited understanding of the role played by particular physical features of interpersonal touch communication. In this study, adults living in Sweden performed a task in which messages (attention, love, happiness, calming, sadness, and gratitude) were conveyed by a sender touching the forearm of a receiver, who interpreted the messages. Two experiments (N = 32, N = 20) showed that within close relationships, receivers could identify the intuitive touch expressions of the senders, and we characterized the physical features of the touches associated with successful communication. Facial expressions measured with electromyography varied by message but were uncorrelated with communication performance. We developed standardized touch expressions and quantified the physical features with 3D hand tracking. In two further experiments (N = 20, N = 16), these standardized expressions were conveyed by trained senders and were readily understood by strangers unacquainted with the senders. Thus, the possibility emerges of a standardized, intuitively understood language of social touch.

BACKGROUND Mortality among patients admitted to intensive care units (ICUs) with COVID-19 is unclear due to variable follow-up periods. Few nationwide data are available to compare risk factors, treatment and outcomes of COVID-19 patients after ICU admission. OBJECTIVE To evaluate baseline characteristics, treatments and 30-day outcomes of patients admitted to Swedish ICUs with COVID-19. DESIGN Registry-based cohort study with prospective data collection. SETTING Admissions to Swedish ICUs from 6 March to 6 May 2020 with laboratory confirmed COVID-19 disease. PARTICIPANTS Adult patients admitted to Swedish ICUs. EXPOSURES Baseline characteristics, intensive care treatments and organ failures. MAIN OUTCOMES AND MEASURES The primary outcome was 30-day all-cause mortality. A multivariable model was used to determine the independent association between potential predictor variables and death. RESULTS We identified 1563 patients with complete 30-day follow-up. The 30-day all-cause mortality was 26.7%. Median age was 61 [52 to 69], Simplified Acute Physiology Score III (SAPS III) was 53 [46 to 59] and 62.5% had at least one comorbidity. Median PaO2/FiO(2) on admission was 97.5 [75.0 to 140.6] mmHg, 74.7% suffered from moderate-to-severe acute respiratory failure. Age, male sex [adjusted odds ratio (aOR) 1.5 (1.1 to 2.2)], SAPS III score [aOR 1.3 (1.2 to 1.4)], severe respiratory failure [aOR 3.0 (2.0 to 4.7)], specific COVID-19 pharmacotherapy [aOR 1.4 (1.0 to 1.9)] and continuous renal replacement therapy [aOR 2.1 (1.5 to 3.0)] were associated with increased mortality. Except for chronic lung disease, the presence of comorbidities was not independently associated with mortality. CONCLUSIONS Thirty-day mortality rate in COVID-19 patients admitted to Swedish ICUs is generally lower than previously reported despite a severe degree of hypoxaemia on admission. Mortality was driven by age, baseline disease severity, the presence and degree of organ failure, rather than pre-existing comorbidities.

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch.

Brushed stimuli are perceived as pleasant when stroked lightly on the skin surface of a touch receiver at certain velocities. While the relationship between brush velocity and pleasantness has been widely replicated, we do not understand how resultant skin movements - e.g., lateral stretch, stick-slip, normal indentation - drive us to form such judgments. In a series of psychophysical experiments, this work modulates skin movements by varying stimulus stiffness and employing various treatments. The stimuli include brushes of three levels of stiffness and an ungloved human finger. The skins friction is modulated via non-hazardous chemicals and washing protocols, and the skins thickness and lateral movement are modulated by thin sheets of adhesive film. The stimuli are hand-brushed at controlled forces and velocities. Human participants report perceived pleasantness per trial using ratio scaling. The results indicate that a brushs stiffness influenced pleasantness more than any skin treatment. Surprisingly, varying the skins friction did not affect pleasantness. However, the application of a thin elastic film modulated pleasantness. Such barriers, though elastic and only 40 microns thick, inhibit the skins tangential movement and disperse normal force. The finding that thin films modulate affective interactions has implications for wearable sensors and actuation devices.

Given emerging evidence that learning to play a musical instrument may lead to a number of cognitive benefits for older adults, it is important to clarify how these training programs can be delivered optimally and meaningfully. The effective acquisition of musical and domain-general skills by later-life learners may be influenced by social, cultural and individual factors within the learning environment. The current study examines the effects of a 10-week piano training program on healthy older adult novices cognitive and motor skills, in comparison to an inactive waitlisted control group. Fifteen participants completed piano training led by a music facilitator in small groups (max n = 4 per lesson class; two experimental, two waitlisted control groups). Data was collected using an explanatory sequential design: quantitative data from a battery of cognitive and motor tests was collected pre/post-test on all participants, with further post-test data from the waitlisted control group (n = 7). Qualitative data included weekly facilitator observations, participant practice diaries, and an individual, semi-structured, post-experiment interview. Bayesian modelling demonstrated moderate evidence of a strong positive impact of training on part A of the Trail Making test (TMT), indicating improved visuo-motor skills. Moderate evidence for negative impacts of training on part B of the Trail Making Test (and difference score delta) was also found, suggesting no benefit of cognitive switching. Qualitative results revealed that the group learning environment motivated participants to play in musical ensembles and to socialize. Motivation was optimal when all participants were happy with the chosen repertoire (participants reported they were motivated by learning to play familiar music) and when the facilitator observed that groups had formed cohesive bonds. Informed by these factors, exploratory analyses demonstrated strong evidence that a participants lesson class had an impact on post-test scores (TMT part A). These results not only demonstrate the extent of cognitive benefits of a short-term piano training intervention for older adults, but also the importance of considering the group dynamics in the learning environment.

Sensing movements across the skin surface is a complex task for the tactile sensory system, relying on sophisticated cortical processing. Functional MRI has shown that judgements of the direction of tactile stimuli moving across the skin are processed in distributed cortical areas in healthy humans. To further study which brain areas are important for tactile direction discrimination, we performed a lesion study, examining a group of patients with first-time stroke. We measured tactile direction discrimination in 44 patients, bilaterally on the dorsum of the hands and feet, within 2 weeks (acute), and again in 28 patients 3 months after stroke. The 3-month follow-up also included a structural MRI scan for lesion delineation. Fifty-nine healthy participants were examined for normative direction discrimination values. We found abnormal tactile direction discrimination in 29/44 patients in the acute phase, and in 21/28 3 months after stroke. Lesions that included the opercular parietal area 1 of the secondary somatosensory cortex, the dorsolateral prefrontal cortex or the insular cortex were always associated with abnormal tactile direction discrimination, consistent with previous functional MRI results. Abnormal tactile direction discrimination was also present with lesions including white matter and subcortical regions. We have thus delineated cortical, subcortical and white matter areas important for tactile direction discrimination function. The findings also suggest that tactile dysfunction is common following stroke.

The temporal pattern of action potentials can convey rich information in a variety of sensory systems. We describe a new non-invasive technique that enables precise, reliable generation of action potential patterns in tactile peripheral afferent neurons by brief taps on the skin. Using this technique, we demonstrate sophisticated coding of temporal information in the somatosensory system, that shows that perceived vibration frequency is not encoded in peripheral afferents as was expected by either their firing rate or the underlying periodicity of the stimulus. Instead, a burst gap or silent gap between trains of action potentials conveys frequency information. This opens the possibility of new encoding strategies that could be deployed to convey sensory information using mechanical or electrical stimulation in neural prostheses and brain-machine interfaces, and may extend to senses beyond artificial encoding of aspects of touch. We argue that a focus on appropriate use of effective temporal coding offers more prospects for rapid improvement in the function of these interfaces than attempts to scale-up existing devices.

Inter-personal touch is a powerful aspect of social interaction that we expect to he particularly important for emotional communication. We studied the capacity of closely acquainted humans to signal the meaning of several word cues (e.g. gratitude, sadness) using touch sensation alone. Participants communicated all cues with above chance performance. We show that emotionally close people can accurately signal the meaning of different words through touch, and that performance is affected by the amount of contextual information available. Even with minimal context and feedback, both attention-getting and love were communicated surprisingly well. Neither the type of close relationship, nor self-reported comfort with touch significantly affected performance.

Human-to-human touch conveys rich, meaningful social and emotional sentiment. At present, however, we understand neither the physical attributes that underlie such touch, nor how the attributes evoke responses in unique types of peripheral afferents. Indeed, nearly all electrophysiological studies use well-controlled but non-ecological stimuli. Here, we develop motion tracking and algorithms to quantify physical attributes indentation depth, shear velocity, contact area, and distance to the cutaneous sensory space (receptive field) of the afferent underlying human-to-human touch. In particular, 2-D video of the scene is combined with 3-D stereo infrared video of the touchers hand to measure contact interactions local to the receptive field of the receivers afferent. The combined and algorithmically corrected measurements improve accuracy, especially of occluded and misidentified fingers. Human subjects experiments track a toucher performing four gestures - single finger tapping, multi-finger tapping, multi-finger stroking and whole hand holding - while action potentials are recorded from a first-order afferent of the receiver. A case study with one rapidly-adapting (Pacinian) and one C-tactile afferent examines temporal ties between gestures and elicited action potentials. The results indicate this method holds promise in determining the roles of unique afferent types in encoding social and emotional touch attributes in their naturalistic delivery.

The established view is that vibrotactile stimuli evoke two qualitatively distinctive cutaneous sensations, flutter (frequencies amp;lt; 60 Hz) and vibratory hum (frequencies amp;gt; 60 Hz), subserved by two distinct receptor types (Meissners and Pacinian corpuscle, respectively), which may engage different neural processing pathways or channels and fulfil quite different biological roles. In psychological and physiological literature, those two systems have been labelled as Pacinian and non-Pacinian channels. However, we present evidence that low-frequency spike trains in Pacinian afferents can readily induce a vibratory percept with the same low frequency attributes as sinusoidal stimuli of the same frequency, thus demonstrating a universal frequency decoding system. We achieved this using brief low-amplitude pulsatile mechanical stimuli to selectively activate Pacinian afferents. This indicates that spiking pattern, regardless of receptor type, determines vibrotactile frequency perception. This mechanism may underlie the constancy of vibrotactile frequency perception across different skin regions innervated by distinct afferent types.

Couples often communicate their emotions, e.g., love or sadness, through physical expressions of touch. Prior efforts have used visual observation to distinguish emotional touch communications by certain gestures tied to ones hand contact, velocity and position. The work herein describes an automated approach to eliciting the essential features of these gestures. First, a tracking system records the timing and location of contact interactions in 3-D between a touchers hand and a receivers forearm. Second, data post-processing algorithms extract dependent measures, derived from prior visual observation, tied to the intensity and velocity of the touchers hand, as well as areas, durations and parts of the hand in contact. Third, behavioral data were obtained from five couples who sought to convey a variety of emotional word cues. We found that certain combinations of six dependent measures well distinguish the touch communications. For example, a typical sadness expression invokes more contact, evolves more slowly, and impresses less deeply into the forearm than a typical attention expression. Furthermore, cluster analysis indicates 2-5 distinct expression strategies are common per word being communicated. Specifying the essential features of touch communications can guide haptic devices in reproducing naturalistic interactions.

Background: HIV-associated distal polyneuropathy (HIV-PN) affects large and small sensory nerve fibers and can cause tactile insensitivity. This exploratory study forms part of an effort to apply subsensory electrical nerve stimulation (SENS) to improve tactile sensitivity of patients with HIV-PN. This work presented an opportunity to use a robust protocol to quantitatively describe the vibrotactile sensitivity of individuals with HIV-PN on effective antiretroviral therapy (ART) and correlate these findings with commonly used clinical vibration testing and scoring grades. Methods: The vibration perception thresholds (VPTs) of 20 patients with HIV-PN at three vibration frequencies (25, 50, and 128 Hz) were measured. We compare the vibration perception threshold (VPT) outcomes to an age- and gender-matched control cohort. We further correlated VPT findings with 128 Hz tuning fork (TF) assessments performed on the HIV-PN participants, accrued as part of a larger study. HIV-PN was defined as having at least one distal symmetrical neuropathic sign, although 18 of 20 had at least two neuropathic signs. Conclusions: HIV-PN participants were found to have lower VPT sensitivity than controls for all three vibration frequencies, and VPT was more sensitive at higher vibration frequencies for both HIV-PN and controls. VPT sensitivity was reduced with older age. Years on ART was correlated with VPT-25 Hz but not with VPT in general. Notably, VPT sensitivity did not correlate with the clinically used 128 Hz TF severity grades. Outcomes of tests for interaction with vibration frequency suggest that HIV-PN pathology does not affect all mechanoreceptors similarly.