Three key questions to move towards a theoretical framework of visuospatial perspective taking.

What would a theory of visuospatial perspective taking (VSPT) look like? Here, ten researchers in the field, many with different theoretical viewpoints and empirical approaches, present their consensus on the three big questions we need to answer in order to bring this theory (or these theories) closer.

Interoceptive abilities facilitate taking another's spatial perspective.

Information can be perceived from a multiplicity of spatial perspectives, which is central to effectively understanding and interacting with our environment and other people. Interoception, the sense of the physiological state of our body, is also a fundamental component contributing to our perception. However, whether the perception of our inner body signals influences our ability to adopt and flexibly change between different spatial perspectives remains poorly understood. To investigate this, 90 participants completed tasks assessing multiple dimensions of interoception (interoceptive sensibility, cardiac interoceptive accuracy and awareness) and the Graphesthesia task to assess tactile spatial perspective-taking and its flexibility. The results revealed that higher cardiac interoceptive awareness is associated with greater consistency in adopting a perspective decentred from the self. Second, higher cardiac interoceptive accuracy was associated with slower and less accurate performance in switching from a decentred to an egocentred perspective. These results show that interoceptive abilities facilitate decentred spatial perspective-taking, likely reflecting stronger perceived boundaries between internal states and the external world.

Mother knows best: Mothers are more egocentric towards their own child's bodily feelings.

Our emotional state can influence how we understand other people's emotions, leading to biases in social understanding. Yet emotional egocentric biases in specific relationships such as parent-child dyads, where not only understanding but also emotional and bodily regulation is key, remain relatively unexplored. To investigate these biases and control for sensory priors, we first conducted two experiments in dyads of adult strangers (total N=75) using a bodily Emotional Egocentricity Task that enables simultaneous affective tactile stimulation within a dyad. We showed its effectiveness in eliciting both classical and sensory-controlled egocentric biases. We then recruited 68 mother-child dyads and found that mothers exhibit higher classical and sensory-controlled emotional egocentric biases towards their own child compared to an unfamiliar child. Results suggest that mothers tend to rely on their bodily feelings more when judging the states of their own child than those of other children, possibly consistent with their regulatory parental role.

Spatial perspective-taking: insights from sensory impairments.

Information can be perceived from a multiplicity of spatial perspectives, which is central to effectively understanding and interacting with our environment and other people. Sensory impairments such as blindness are known to impact spatial representations and perspective-taking is often thought of as a visual process. However, disturbed functioning of other sensory systems (e.g., vestibular, proprioceptive and auditory) can also influence spatial perspective-taking. These lines of research remain largely separate, yet together they may shed new light on the role that each sensory modality plays in this core cognitive ability. The findings to date reveal that spatial cognitive processes may be differently affected by various types of sensory loss. The visual system may be crucial for the development of efficient allocentric (object-to-object) representation; however, the role of vision in adopting another's spatial perspective remains unclear. On the other hand, the vestibular and the proprioceptive systems likely play an important role in anchoring the perceived self to the physical body, thus facilitating imagined self-rotations required to adopt another's spatial perspective. Findings regarding the influence of disturbed auditory functioning on perspective-taking are so far inconclusive and thus await further data. This review highlights that spatial perspective-taking is a highly plastic cognitive ability, as the brain is often able to compensate in the face of different sensory loss.

Social touch deprivation during COVID-19: effects on psychological wellbeing and craving interpersonal touch.

Social touch has positive effects on social affiliation and stress alleviation. However, its ubiquitous presence in human life does not allow the study of social touch deprivation 'in the wild'. Nevertheless, COVID-19-related restrictions such as social distancing allowed the systematic study of the degree to which social distancing affects tactile experiences and mental health. In this study, 1746 participants completed an online survey to examine intimate, friendly and professional touch experiences during COVID-19-related restrictions, their impact on mental health and the extent to which touch deprivation results in craving touch. We found that intimate touch deprivation during COVID-19-related restrictions is associated with higher anxiety and greater loneliness even though this type of touch is still the most experienced during the pandemic. Moreover, intimate touch is reported as the type of touch most craved during this period, thus being more prominent as the days practising social distancing increase. However, our results also show that the degree to which individuals crave touch during this period depends on individual differences in attachment style: the more anxiously attached, the more touch is craved; with the reverse pattern for avoidantly attached. These findings point to the important role of interpersonal and particularly intimate touch in times of distress and uncertainty.

Interactions between interoception and perspective-taking: Current state of research and future directions.

Interoception, the sense of the physiological state of the body, and perspective-taking, the ability to take another's point of view, are two fundamental components contributing to our perception and interaction with the external world. However, whether the perception of our inner body influences how we perceive the external world and other people remains poorly understood. Here, we review recent behavioural and neuroimaging evidence investigating the links between dimensions of interoception (i.e., accuracy, sensibility and awareness) and perspective-taking (i.e., affective, cognitive and visual). So far, only a limited subset of these dimensions has been investigated together and the results suggest that interoceptive abilities may only interact with perspective-taking when embodied mental transformations are required. Furthermore, mainly the emotional aspects of perspective-taking are related to interoception, influencing the ability to empathise with others. Future research should systematically investigate the links between all dimensions of interoception and perspective-taking to provide full understanding of the specific role interoception has on how we perceive the world and take another's point of view.

Updating beliefs beyond the here-and-now: the counter-factual self in anosognosia for hemiplegia.

The syndrome of anosognosia for hemiplegia, or the lack of awareness for one's paralysis following right hemisphere stroke, can provide unique insights into the neurocognitive mechanisms of self-awareness. Yet it remains unclear whether anosognosia for hemiplegia is a modality-specific deficit of sensorimotor monitoring, or whether domain-general processes of attention and belief-updating converge to cause anosognosia for hemiplegia. Using a Bayesian learning framework, we formalized and empirically investigated the hypothesis that failures to update anosognosic beliefs can be explained by abnormalities in the relative uncertainty (i.e. precision) ascribed to prior beliefs versus sensory information in different contexts. We designed a new motor belief-updating task that manipulated both the temporal (prospective and retrospective) and spatial (hemispace most affected by inattention and hemispace less affected by inattention) conditions in which beliefs had to be updated, and we validated its sensitivity to anosognosia for hemiplegia in 26 patients with right hemisphere stroke. We then computed and empirically tested two different Bayesian predictors of prospective beliefs using two proxies for precision in anosognosia for hemiplegia patients: (i) standardized, neuropsychological measures of objective attention abilities, i.e. visuospatial neglect scores and (ii) subjective uncertainty reports, i.e. confidence ratings. Our results suggest that while neglect does not affect local, sensorimotor error monitoring, it does seem to affect the degree to which observed errors are used to update more general, prospective beliefs about counterfactual motor abilities in anosognosia for hemiplegia. Difficulties in such 'counterfactual' belief-updating were associated with disruptions in tracts of the ventral attentional network (i.e. superior longitudinal fasciculus connecting the temporo-parietal junction and ventral frontal cortex) and associated lesions to the insula, inferior parietal cortex and superior temporal regions. These results suggest that self-awareness extends beyond local, retrospective monitoring, requiring also salience-based, convergence of beliefs about the self that go beyond the 'here-and-now' of sensorimotor experience.

Exploring three levels of interoception in people with functional motor disorders.

INTRODUCTION: A three-level model of interoception has recently been defined. We aim to study the interoceptive processing in individuals with functional motor disorder (FMD). METHODS: Twenty-two patients with FMD were compared to 23 healthy controls. They underwent a protocol measuring different levels of interoception including: accuracy (a heart-beat tracking task), awareness (participant's confidence level) and sensibility (the Body Awareness Questionnaire-BAQ). Depression, anxiety and alexithymia were assessed by means of validated clinical scales. RESULTS: The FMD group showed a lower cardiac interoceptive accuracy and sensibility than healthy controls but they did not differ in terms of awareness (p = 0.03 and 0.005 respectively). They were aware of their poor performance in the accuracy task. Cardiac interoceptive accuracy positively correlated with the BAQ sub-scales "Predict Body Reaction" (r = 0.49, p = 0.001) and "Sleep-Wake Cycle" (r = 0.52, p < 0.001). A mediation analysis showed a significant indirect effect of group on cardiac interoceptive accuracy through BAQ "Predict Body Reaction" (b = -2.95, 95% BCa CI[-7.2;-0.2]). The direct effect of group on "Predict Body Reaction" was still significant (b = - 6.95, p = 0.02, 95% CI[-13.18;-0.73]). CONCLUSIONS: People with FMD have impaired cardiac interoceptive accuracy and sensibility but no difference in metacognitive interoception compared to healthy controls.

Dissociating embodiment and emotional reactivity in motor responses to artworks.

Perceiving art is known to elicit motor cortex activation in an observer's brain. This motor activation has often been attributed to a covert approach response associated with the emotional valence of an art piece (emotional reaction hypothesis). However, recent accounts have proposed that aesthetic experiences could be grounded in the motor simulation of actions required to produce an art piece and of the sensorimotor states embedded in its subject (embodied aesthetic hypothesis). Here, we aimed to test these two hypotheses by assessing whether motor facilitation during artwork perception mirrors emotional or motor simulation processes. To this aim, we capitalized on single pulse transcranial magnetic stimulation revealing a two-stage motor coding of emotional body postures: an early, non-specific activation related to emotion processing and a later action-specific activation reflecting motor simulation. We asked art-naïve individuals to rate how much they liked a series of pointillist and brushstroke canvases; photographs of artistic gardens served as control natural stimuli. After an early (150 ms) or a later (300 ms) post-stimulus delay, motor evoked potentials were recorded from wrist-extensor and finger muscles that were more involved in brushstroke- and pointillist-like painting, respectively. Results showed that observing the two canvas styles did not elicit differential motor activation in the early time window for either muscle, not supporting the emotional reaction hypothesis. However, in support of the embodied aesthetic hypothesis, we found in the later time window greater motor activation responses to brushstroke than pointillist canvases for the wrist-extensor, but not for the finger muscle. Furthermore, this muscle-selective facilitation was associated with lower liking ratings of brushstroke canvases and with greater empathy dispositions. These findings support the claim that simulation of the painter's movements is crucial for aesthetic experience, by documenting a link between motor simulation, dispositional empathy, and subjective appreciation in artwork perception.

Vision shapes tactile spatial perspective taking.

Information from the environment can be perceived according to ego-centered or decentered spatial perspectives. Different spatial perspectives can be adopted when perceiving not only visual but also auditory or tactile information. Because vision may be dominant in setting up spatial information processing, visual loss might affect perspective taking in other sensory modalities. The present study investigated the influence of vision on the perspective that is adopted naturally and the influence of visual experience on the ability to switch between perspectives in the tactile domain. Participants with varying degrees of visual experience (early blind, late blind, blindfolded-sighted, and sighted) completed a tactile recognition task of ambiguous letter stimuli ("b," "d," "p," and "q") presented on the body, for which 3 perspectives can be adopted (trunk centered, head centered, and decentered). The participants were first free to adopt any perspective they wanted before either the same or a different perspective was imposed. The results showed that both a temporary and a permanent lack of vision promote spontaneous adoption of ego-centered spatial coordinates, anchored to the head. Moreover, more decentered coordinates were adopted by the blindfolded-sighted compared with the early and late blind, suggesting that blindness reduces the adoption of decentered perspectives. Finally, the early blind exhibited a greater cost of switching perspectives compared with the sighted, suggesting that early visual experience is important for flexible perspective taking. Overall, our study reveals that vision shapes both the naturally adopted perspective and the flexibility to change perspective. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Harnessing tactile waves to measure skin-to-skin interactions.

Skin-to-skin touch is an essential form of tactile interaction, yet there is no known method to quantify how we touch our own skin or someone else's skin. Skin-to-skin touch is particularly challenging to measure objectively, since interposing an instrumented sheet, no matter how thin and flexible, between the interacting skins is not an option. To fill this gap, we explored a technique that takes advantage of the propagation of vibrations from the locus of touch to pick up a signal that contains information about skin-to-skin tactile interactions. These "tactile waves" were measured by an accelerometer sensor placed on the touching finger. Applied pressure and speed had a direct influence on measured signal power when the target of touch was the self or another person. The measurements were insensitive to changes in the location of the sensor relative to the target. Our study suggests that this method has potential for probing behaviour during skin-to-skin tactile interactions and could be a valuable technique to study social touch, self-touch, and motor control. The method is non-invasive, easy to commission, inexpensive, and robust.

Welcoming back my arm: affective touch increases body ownership following right-hemisphere stroke.

Right-hemisphere stroke can impair the ability to recognize one's contralesional body parts as belonging to one's self. The study of this so-called 'disturbed sense of limb ownership' can provide unique insights into the neurocognitive mechanisms of body ownership. In this study, we address a hypothesis built upon experimental studies on body ownership in healthy volunteers. These studies have shown that affective (pleasant) touch, an interoceptive modality associated with unmyelinated, slow-conducting C-tactile afferents, has a unique role in the sense of body ownership. In this study, we systematically investigated whether affective touch stimulation could increase body ownership in patients with a disturbed sense of limb ownership following right-hemisphere stroke. An initial feasibility study in 16 adult patients with acute stroke enabled us to optimize and calibrate an affective touch protocol to be administered by the bedside. The main experiment, conducted with a different sample of 26 right hemisphere patients, assessed changes in limb ownership elicited following self- (patient) versus other- (experimenter) generated tactile stimulation, using a velocity known to optimally activate C-tactile fibres (i.e. 3 cm/s), and a second velocity that is suboptimal for C-tactile activation (i.e. 18 cm/s). We further examined the specificity and mechanism of observed changes in limb ownership in secondary analyses looking at (i) the influence of perceived intensity and pleasantness of touch, (ii) touch laterality and (iii) level of disturbed sense of limb ownership on ownership change and (iv) changes in unilateral neglect arising from touch. Findings indicated a significant increase in limb ownership following experimenter-administered, C-tactile-optimal touch. Voxel-based lesion-symptom mapping identified damage to the right insula and, more substantially, the right corpus callosum, associated with a failure to increase body ownership following experimenter-administered, affective touch. Our findings suggest that affective touch can increase the sense of body-part ownership following right-hemisphere stroke, potentially due to its unique role in the multisensory integration processes that underlie the sense of body ownership.

Damage to the right insula disrupts the perception of affective touch.

Specific, peripheral C-tactile afferents contribute to the perception of tactile pleasure, but the brain areas involved in their processing remain debated. We report the first human lesion study on the perception of C-tactile touch in right hemisphere stroke patients (N = 59), revealing that right posterior and anterior insula lesions reduce tactile, contralateral and ipsilateral pleasantness sensitivity, respectively. These findings corroborate previous imaging studies regarding the role of the posterior insula in the perception of affective touch. However, our findings about the crucial role of the anterior insula for ipsilateral affective touch perception open new avenues of enquiry regarding the cortical organization of this tactile system.

Mixing up the Senses: Sensory Substitution Is Not a Form of Artificially Induced Synaesthesia.

Sensory Substitution Devices (SSDs) are typically used to restore functionality of a sensory modality that has been lost, like vision for the blind, by recruiting another sensory modality such as touch or audition. Sensory substitution has given rise to many debates in psychology, neuroscience and philosophy regarding the nature of experience when using SSDs. Questions first arose as to whether the experience of sensory substitution is represented by the substituted information, the substituting information, or a multisensory combination of the two. More recently, parallels have been drawn between sensory substitution and synaesthesia, a rare condition in which individuals involuntarily experience a percept in one sensory or cognitive pathway when another one is stimulated. Here, we explore the efficacy of understanding sensory substitution as a form of 'artificial synaesthesia'. We identify several problems with previous suggestions for a link between these two phenomena. Furthermore, we find that sensory substitution does not fulfil the essential criteria that characterise synaesthesia. We conclude that sensory substitution and synaesthesia are independent of each other and thus, the 'artificial synaesthesia' view of sensory substitution should be rejected.

Vestibular modulation of multisensory integration during actual and vicarious tactile stimulation.

The vestibular system has been shown to contribute to multisensory integration by balancing conflictual sensory information. It remains unclear whether such modulation of exteroceptive (e.g., vision), proprioceptive, and interoceptive (e.g., affective touch) sensory sources is influenced by epistemically different aspects of tactile stimulation (i.e., felt from within vs. seen, vicarious touch). In the current study, we aimed to (a) replicate previous findings regarding the effects of galvanic stimulation of the right vestibular network in multisensory integration, and (b) examine vestibular contributions to multisensory integration when touch is felt but not seen (and vice versa). During artificial vestibular stimulation (LGVS, i.e., right vestibular stimulation), RGVS (i.e., bilateral stimulation), and sham (i.e., placebo stimulation), healthy participants (N = 36, Experiment 1; N = 37, Experiment 2) looked at a rubber hand while either their own unseen hand or the rubber hand were touched by affective or neutral touch. We found that (a) LGVS led to enhancement of vision over proprioception during visual only conditions (replicating our previous findings), and (b) LGVS (versus sham) favored proprioception over vision when touch was felt (Experiment 1), with the opposite results when touch was vicariously perceived via vision (Experiment 2) and with no difference between affective and neutral touch. We showed how vestibular signals modulate the weight of each sensory modality according to the context in which they are perceived and that such modulation extends to different aspects of tactile stimulation: felt and seen touch are differentially balanced in multisensory integration according to their epistemic relevance.

Affective certainty and congruency of touch modulate the experience of the rubber hand illusion.

Our sense of body ownership relies on integrating different sensations according to their temporal and spatial congruency. Nevertheless, there is ongoing controversy about the role of affective congruency during multisensory integration, i.e. whether the stimuli to be perceived by the different sensory channels are congruent or incongruent in terms of their affective quality. In the present study, we applied a widely used multisensory integration paradigm, the Rubber Hand Illusion, to investigate the role of affective, top-down aspects of sensory congruency between visual and tactile modalities in the sense of body ownership. In Experiment 1 (N = 36), we touched participants with either soft or rough fabrics in their unseen hand, while they watched a rubber hand been touched synchronously with the same fabric or with a 'hidden' fabric of 'uncertain roughness'. In Experiment 2 (N = 50), we used the same paradigm as in Experiment 1, but replaced the 'uncertainty' condition with an 'incongruent' one, in which participants saw the rubber hand being touched with a fabric of incongruent roughness and hence opposite valence. We found that certainty (Experiment 1) and congruency (Experiment 2) between the felt and vicariously perceived tactile affectivity led to higher subjective embodiment compared to uncertainty and incongruency, respectively, irrespective of any valence effect. Our results suggest that congruency in the affective top-down aspects of sensory stimulation is important to the multisensory integration process leading to embodiment, over and above temporal and spatial properties.

Dance Training Shapes Action Perception and Its Neural Implementation within the Young and Older Adult Brain.

How we perceive others in action is shaped by our prior experience. Many factors influence brain responses when observing others in action, including training in a particular physical skill, such as sport or dance, and also general development and aging processes. Here, we investigate how learning a complex motor skill shapes neural and behavioural responses among a dance-naïve sample of 20 young and 19 older adults. Across four days, participants physically rehearsed one set of dance sequences, observed a second set, and a third set remained untrained. Functional MRI was obtained prior to and immediately following training. Participants' behavioural performance on motor and visual tasks improved across the training period, with younger adults showing steeper performance gains than older adults. At the brain level, both age groups demonstrated decreased sensorimotor cortical engagement after physical training, with younger adults showing more pronounced decreases in inferior parietal activity compared to older adults. Neural decoding results demonstrate that among both age groups, visual and motor regions contain experience-specific representations of new motor learning. By combining behavioural measures of performance with univariate and multivariate measures of brain activity, we can start to build a more complete picture of age-related changes in experience-dependent plasticity.

Balancing body ownership: Visual capture of proprioception and affectivity during vestibular stimulation.

The experience of our body as our own (i.e. body ownership) involves integrating different sensory signals according to their contextual relevance (i.e. multisensory integration). Until recently, most studies of multisensory integration and body ownership concerned only vision, touch and proprioception; the role of other modalities, such as the vestibular system and interoception, has been neglected and remains poorly understood. In particular, no study to date has directly explored the combined effect of vestibular and interoceptive signals on body ownership. Here, we investigated for the first time how Galvanic Vestibular Stimulation (left, right, sham), tactile affectivity (a reclassified interoceptive modality manipulated by applying touch at C-tactile optimal versus non-optimal velocities), and their combination, influence proprioceptive and subjective measures of body ownership during a rubber hand illusion paradigm with healthy participants (N = 26). Our results show that vestibular stimulation (left GVS) significantly increased proprioceptive drift towards the rubber hand during mere visual exposure to the rubber hand. Moreover, it also enhanced participants' proprioceptive drift towards the rubber hand during manipulations of synchronicity and affective touch. These findings suggest that the vestibular system influences multisensory integration, possibly by re-weighting both the two-way relationship between proprioception and vision, as well as the three-way relationship between proprioception, vision and affective touch. We discuss these findings in relation to current predictive coding models of multisensory integration and body ownership.

Neurodevelopmental perspectives on dance learning: Insights from early adolescence and young adulthood.

Studies investigating human motor learning and movement perception have shown that similar sensorimotor brain regions are engaged when we observe or perform action sequences. However, the way these networks enable translation of complex observed actions into motor commands-such as in the context of dance-remains poorly understood. Emerging evidence suggests that the ability to encode specific visuospatial and kinematic movement properties encountered via different routes of sensorimotor experience may be an integral component of action learning throughout development. Using a video game-based dance training paradigm, we demonstrate that patterns of voxel activity in visual and sensorimotor brain regions when perceiving movements following training are related to the sensory modalities through which these movements were encountered during whole-body dance training. Compared to adolescents, young adults in this study demonstrated more distinctive patterns of voxel activity in visual cortices in relation to different types of sensorimotor experience. This finding suggests that cortical maturity might influence the extent to which prior sensorimotor experiences shape brain activity when watching others in action, and potentially impact how we acquire new motor skills.

The influence of sensorimotor experience on the aesthetic evaluation of dance across the life span.

Understanding how action perception, embodiment, and emotion interact is essential for advancing knowledge about how we perceive and interact with each other in a social world. One tool that has proved particularly useful in the past decade for exploring the relationship between perception, action, and affect is dance. Dance is, in its essence, a rich and multisensory art form that can be used to help answer not only basic questions about social cognition but also questions concerning how aging shapes the relationship between action perception, and the role played by affect, emotion, and aesthetics in social perception. In the present study, we used a 1-week physical and visual dance training paradigm to instill varying degrees of sensorimotor experience among non-dancers from three distinct age groups (early adolescents, young adults, and older adults). Our aim was to begin to build an understanding of how aging influences the relationship between action embodiment and affective (or aesthetic) value, at both brain and behavioral levels. On balance, our results point toward a similar positive effect of sensorimotor training on aesthetic evaluations across the life span on a behavioral level, but to rather different neural substrates supporting implicit aesthetic judgment of dance movements at different life stages. Taken together, the present study contributes valuable first insights into the relationship between sensorimotor experience and affective evaluations across ages, and underscores the utility of dance as a stimulus and training intervention for addressing key questions relevant to human neuroscience as well as the arts and humanities.