Am I seeing my hand? Visual appearance and knowledge of controllability both contribute to the visual capture of a person's own body

When confronted with complex visual scenes in daily life, how do we know which visual information represents our own hand? We investigated the cues used to assign visual information to one''s own hand. Wrist tendon vibration elicits an illusory sensation of wrist movement. The intensity of this illusion attenuates when the actual motionless hand is visually presented. Testing what kind of visual stimuli attenuate this illusion will elucidate factors contributing to visual detection of one''s own hand. The illusion was reduced when a stationary object was shown, but only when participants knew it was controllable with their hands. In contrast, the visual image of their own hand attenuated the illusion even when participants knew that it was not controllable. We suggest that long-term knowledge about the appearance of the body and short-term knowledge about controllability of a visual object are combined to robustly extract our own body from a visual scene.     

The body beyond the body: expectation of a sensory event is enough to induce ownership over a fake hand

More than 100 papers have been published on the rubber hand illusion since its discovery 14 years ago. The illusion has been proposed as a demonstration that the body is distinguished from other objects by its participation in specific forms of intermodal perceptual correlation. Here, we radically challenge this view by claiming that perceptual correlation is not necessary to produce the experience of this body as mine. Each of 15 participants was seated with his/her right arm resting upon a table just below another smaller table. Thus, the real hand was hidden from the participant''s view and a life-sized rubber model of a right hand was placed on the small table in front of the participant. The participant observed the experimenter''s hand while approaching—without touching—the rubber hand. Phenomenology of the illusion was measured by means of skin conductance response and questionnaire. Both measures indicated that participants experienced the illusion that the experimenter''s hand was about to touch their hidden hand rather than the rubber hand, as if the latter replaced their own hand. This did not occur when the rubber hand was rotated by 180° or replaced by a piece of wood. This illusion indicates that our brain does not build a sense of self in a merely reactive way, via perceptual correlations; rather it generates predictions on what may or may not belong to itself.     

Looking for Myself: Current Multisensory Input Alters Self-Face Recognition

How do I know the person I see in the mirror is really me? Is it because I know the person simply looks like me, or is it because the mirror reflection moves when I move, and I see it being touched when I feel touch myself? Studies of face-recognition suggest that visual recognition of stored visual features inform self-face recognition. In contrast, body-recognition studies conclude that multisensory integration is the main cue to selfhood. The present study investigates for the first time the specific contribution of current multisensory input for self-face recognition. Participants were stroked on their face while they were looking at a morphed face being touched in synchrony or asynchrony. Before and after the visuo-tactile stimulation participants performed a self-recognition task. The results show that multisensory signals have a significant effect on self-face recognition. Synchronous tactile stimulation while watching another person''s face being similarly touched produced a bias in recognizing one''s own face, in the direction of the other person included in the representation of one''s own face. Multisensory integration can update cognitive representations of one''s body, such as the sense of ownership. The present study extends this converging evidence by showing that the correlation of synchronous multisensory signals also updates the representation of one''s face. The face is a key feature of our identity, but at the same time is a source of rich multisensory experiences used to maintain or update self-representations.     

The illusion of owning a third arm

Could it be possible that, in the not-so-distant future, we will be able to reshape the human body so as to have extra limbs? A third arm helping us out with the weekly shopping in the local grocery store, or an extra artificial limb assisting a paralysed person? Here we report a perceptual illusion in which a rubber right hand, placed beside the real hand in full view of the participant, is perceived as a supernumerary limb belonging to the participant''s own body. This effect was supported by questionnaire data in conjunction with physiological evidence obtained from skin conductance responses when physically threatening either the rubber hand or the real one. In four well-controlled experiments, we demonstrate the minimal required conditions for the elicitation of this “supernumerary hand illusion”. In the fifth, and final experiment, we show that the illusion reported here is qualitatively different from the traditional rubber hand illusion as it is characterised by less disownership of the real hand and a stronger feeling of having two right hands. These results suggest that the artificial hand ‘borrows’ some of the multisensory processes that represent the real hand, leading to duplication of touch and ownership of two right arms. This work represents a major advance because it challenges the traditional view of the gross morphology of the human body as a fundamental constraint on what we can come to experience as our physical self, by showing that the body representation can easily be updated to incorporate an additional limb.     

The Effect of Self-Efficacy on Visual Discrimination Sensitivity

Can subjective belief about one''s own perceptual competence change one''s perception? To address this question, we investigated the influence of self-efficacy on sensory discrimination in two low-level visual tasks: contrast and orientation discrimination. We utilised a pre-post manipulation approach whereby two experimental groups (high and low self-efficacy) and a control group made objective perceptual judgments on the contrast or the orientation of the visual stimuli. High and low self-efficacy were induced by the provision of fake social-comparative performance feedback and fictional research findings. Subsequently, the post-manipulation phase was performed to assess changes in visual discrimination thresholds as a function of the self-efficacy manipulations. The results showed that the high self-efficacy group demonstrated greater improvement in visual discrimination sensitivity compared to both the low self-efficacy and control groups. These findings suggest that subjective beliefs about one''s own perceptual competence can affect low-level visual processing.     

Self-Recognition of One's Own Fall Recruits the Genuine Bodily Crisis-Related Brain Activity

While bipedalism is a fundamental evolutionary adaptation thought to be essential for the development of the human brain, the erect body is always an inch or two away from falling. Although the neural mechanism for automatically detecting one''s own body instability is an important consideration, there have thus far been few functional neuroimaging studies because of the restrictions placed on participants'' movements. Here, we used functional magnetic resonance imaging to investigate the neural substrate underlying whole body instability, based on the self-recognition paradigm that uses video stimuli consisting of one''s own and others'' whole bodies depicted in stable and unstable states. Analyses revealed significant activity in the regions which would be activated during genuine unstable bodily states: The right parieto-insular vestibular cortex, inferior frontal junction, posterior insula and parabrachial nucleus. We argue that these right-lateralized cortical and brainstem regions mediate vestibular information processing for detection of vestibular anomalies, defensive motor responding in which the necessary motor responses are automatically prepared/simulated to protect one''s own body, and sympathetic activity as a form of alarm response during whole body instability.     

The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants'' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one''s own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one''s own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm.The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI.The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.     

Explaining Away the Body: Experiences of Supernaturally Caused Touch and Touch on Non-Hand Objects within the Rubber Hand Illusion

Background

In rubber hand illusions and full body illusions, touch sensations are projected to non-body objects such as rubber hands, dolls or virtual bodies. The robustness, limits and further perceptual consequences of such illusions are not yet fully explored or understood. A number of experiments are reported that test the limits of a variant of the rubber hand illusion.

Methodology/Principal Findings

A variant of the rubber hand illusion is explored, in which the real and foreign hands are aligned in personal space. The presence of the illusion is ascertained with participants'' scores and temperature changes of the real arm. This generates a basic illusion of touch projected to a foreign arm. Participants are presented with further, unusual visuotactile stimuli subsequent to onset of the basic illusion. Such further visuotactile stimulation is found to generate very unusual experiences of supernatural touch and touch on a non-hand object. The finding of touch on a non-hand object conflicts with prior findings, and to resolve this conflict a further hypothesis is successfully tested: that without prior onset of the basic illusion this unusual experience does not occur.

Conclusions/Significance

A rubber hand illusion is found that can arise when the real and the foreign arm are aligned in personal space. This illusion persists through periods of no tactile stimulation and is strong enough to allow very unusual experiences of touch felt on a cardboard box and experiences of touch produced at a distance, as if by supernatural causation. These findings suggest that one''s visual body image is explained away during experience of the illusion and they may be of further importance to understanding the role of experience in delusion formation. The findings of touch on non-hand objects may help reconcile conflicting results in this area of research. In addition, new evidence is provided that relates to the recently discovered psychologically induced temperature changes that occur during the illusion.     

Action Possibility Judgments of People with Varying Motor Abilities Due to Spinal Cord Injury

Predictions about one''s own action capabilities as well as the action capabilities of others are thought to be based on a simulation process involving linked perceptual and motor networks. Given the central role of motor experience in the formation of these networks, one''s present motor capabilities are thought to be the basis of their perceptual judgments about actions. However, it remains unknown whether the ability to form these action possibility judgments is affected by performance related changes in the motor system. To determine if judgments of action capabilities are affected by long-term changes in one''s own motor capabilities, participants with different degrees of upper-limb function due to their level (cervical vs. below cervical) of spinal cord injury (SCI) were tested on a perceptual-motor judgment task. Participants observed apparent motion videos of reciprocal aiming movements with varying levels of difficulty. For each movement, participants determined the shortest movement time (MT) at which they themselves and a young adult could perform the task while maintaining accuracy. Participants also performed the task. Analyses of MTs revealed that perceptual judgments for participant''s own movement capabilities were consistent with their actual performance- people with cervical SCI had longer judged and actual MTs than people with below cervical SCI. However, there were no between-group differences in judged MTs for the young adult. Although it is unclear how the judgments were adjusted (altered simulation vs. threshold modification), the data reveal that people with different motor capabilities due to SCI are not completely biased by their present capabilities and can effectively adjust their judgments to estimate the actions of others.     

Exploring Responses to Art in Adolescence: A Behavioral and Eye-Tracking Study

Adolescence is a peculiar age mainly characterized by physical and psychological changes that may affect the perception of one''s own and others'' body. This perceptual peculiarity may influence the way in which bottom-up and top-down processes interact and, consequently, the perception and evaluation of art. This study is aimed at investigating, by means of the eye-tracking technique, the visual explorative behavior of adolescents while looking at paintings. Sixteen color paintings, categorized as dynamic and static, were presented to twenty adolescents; half of the images represented natural environments and half human individuals; all stimuli were displayed under aesthetic and movement judgment tasks. Participants'' ratings revealed that, generally, nature images are explicitly evaluated as more appealing than human images. Eye movement data, on the other hand, showed that the human body exerts a strong power in orienting and attracting visual attention and that, in adolescence, it plays a fundamental role during aesthetic experience. In particular, adolescents seem to approach human-content images by giving priority to elements calling forth movement and action, supporting the embodiment theory of aesthetic perception.     

New Data on the Problem of Social Perception (A Person's Perception and Conception of Another Person)

Throughout the world at the present time more and more scientists are working on the problem of social perception. Though they are interested in different aspects of this problem, all are helping to elucidate the more or less complex features that characterize the process of how a human being forms images of other people and how he develops conceptions of their personalities. It was no slip of the pen when we included as a part of "social perception" the evolution of one's conception of another human being as a personality, for today the term "social perception" has been extended by most psychologists working on this problem to include the whole range of phenomena involved in one person's knowledge of another on the level of feeling as well as on the rational plane.     

Brain Regions Associated to a Kinesthetic Illusion Evoked by Watching a Video of One's Own Moving Hand

It is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision…). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functional magnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else''s moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibration-induced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primary motor and somatosensory areas. We conclude that under some conditions watching a video of one''s own moving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving.     

Can male Eurasian jays disengage from their own current desire to feed the female what she wants?

Humans'' predictions of another person''s behaviour are regularly influenced by what they themselves might know or want. In a previous study, we found that male Eurasian jays (Garrulus glandarius) could cater for their female partner''s current desire when sharing food with her. Here, we tested the extent to which the males'' decisions are influenced by their own current desire. When the males'' and female''s desires matched, males correctly shared the food that was desired by both. When the female''s desire differed from their own, the males'' decisions were not entirely driven by their own desires, suggesting that males also took the female''s desire into account. Thus, the male jays'' decisions about their mates'' desires are partially biased by their own desire and might be based upon similar processes as those found in humans.     

Neural substrate of body size: illusory feeling of shrinking of the waist

The perception of the size and shape of one's body (body image) is a fundamental aspect of how we experience ourselves. We studied the neural correlates underlying perceived changes in the relative size of body parts by using a perceptual illusion in which participants felt that their waist was shrinking. We scanned the brains of the participants using functional magnetic resonance imaging. We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking. These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex. Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.     

Social cognition and psychopathology: a critical overview

The philosophical and interdisciplinary debate about the nature of social cognition, and the processes involved, has important implications for psychiatry. On one account, mindreading depends on making theoretical inferences about another person''s mental states based on knowledge of folk psychology, the so-called “theory theory” (TT). On a different account, “simulation theory” (ST), mindreading depends on simulating the other''s mental states within one''s own mental or motor system. A third approach, “interaction theory” (IT), looks to embodied processes (involving movement, gesture, facial expression, vocal intonation, etc.) and the dynamics of intersubjective interactions (joint attention, joint action, and processes not confined to an individual system) in highly contextualized situations to explain social cognition, and disruptions of these processes in some psychopathological conditions. In this paper, we present a brief summary of these three theoretical frameworks (TT, ST, IT). We then focus on impaired social abilities in autism and schizophrenia from the perspective of the three approaches. We discuss the limitations of such approaches in the scientific studies of these and other pathologies, and we close with a short reflection on the future of the field. In this regard we argue that, to the extent that TT, ST and IT offer explanations that capture different (limited) aspects of social cognition, a pluralist approach might be best.     

Self‐Euthanasia,the Dutch Experience: In Search for the Meaning of a Good Death or Eu Thanatos

My main purpose in this article is to establish the meaning of a ‘good death’ when death is self‐chosen. I will take as my point of departure the new notion of ‘self‐euthanasia’ and the corresponding practice that has evolved in the Netherlands in recent years. Both physician‐euthanasia and self‐euthanasia refer to an ideal process of a good death, the first being ultimately the physician's responsibility, while the second is definitely the responsibility of the individual choosing to die. However, if we also accept the existence of a fundamental moral difference between ending another person's life and ending your own life, and if we accept this moral difference to be also relevant to the normatively laden good death, then this difference represents a strong reason for preferring self‐euthanasia to physician‐euthanasia.     

The Spread of Sleep Loss Influences Drug Use in Adolescent Social Networks

Troubled sleep is a commonly cited consequence of adolescent drug use, but it has rarely been studied as a cause. Nor have there been any studies of the extent to which sleep behavior can spread in social networks from person to person to person. Here we map the social networks of 8,349 adolescents in order to study how sleep behavior spreads, how drug use behavior spreads, and how a friend''s sleep behavior influences one''s own drug use. We find clusters of poor sleep behavior and drug use that extend up to four degrees of separation (to one''s friends'' friends'' friends'' friends) in the social network. Prospective regression models show that being central in the network negatively influences future sleep outcomes, but not vice versa. Moreover, if a friend sleeps ≤7 hours, it increases the likelihood a person sleeps ≤7 hours by 11%. If a friend uses marijuana, it increases the likelihood of marijuana use by 110%. Finally, the likelihood that an individual uses drugs increases by 19% when a friend sleeps ≤7 hours, and a mediation analysis shows that 20% of this effect results from the spread of sleep behavior from one person to another. This is the first study to suggest that the spread of one behavior in social networks influences the spread of another. The results indicate that interventions should focus on healthy sleep to prevent drug use and targeting specific individuals may improve outcomes across the entire social network.     

Does Seeing Ice Really Feel Cold? Visual-Thermal Interaction under an Illusory Body-Ownership

Although visual information seems to affect thermal perception (e.g. red color is associated with heat), previous studies have failed to demonstrate the interaction between visual and thermal senses. However, it has been reported that humans feel an illusory thermal sensation in conjunction with an apparently-thermal visual stimulus placed on a prosthetic hand in the rubber hand illusion (RHI) wherein an individual feels that a prosthetic (rubber) hand belongs to him/her. This study tests the possibility that the ownership of the body surface on which a visual stimulus is placed enhances the likelihood of a visual-thermal interaction. We orthogonally manipulated three variables: induced hand-ownership, visually-presented thermal information, and tactically-presented physical thermal information. Results indicated that the sight of an apparently-thermal object on a rubber hand that is illusorily perceived as one''s own hand affects thermal judgments about the object physically touching this hand. This effect was not observed without the RHI. The importance of ownership of a body part that is touched by the visual object on the visual-thermal interaction is discussed.     

A cross-culture,cross-gender comparison of perspective taking mechanisms

Being able to judge another person''s visuo-spatial perspective is an essential social skill, hence we investigated the generalizability of the involved mechanisms across cultures and genders. Developmental, cross-species, and our own previous research suggest that two different forms of perspective taking can be distinguished, which are subserved by two distinct mechanisms. The simpler form relies on inferring another''s line-of-sight, whereas the more complex form depends on embodied transformation into the other''s orientation in form of a simulated body rotation. Our current results suggest that, in principle, the same basic mechanisms are employed by males and females in both, East-Asian (EA; Chinese) and Western culture. However, we also confirmed the hypothesis that Westerners show an egocentric bias, whereas EAs reveal an other-oriented bias. Furthermore, Westerners were slower overall than EAs and showed stronger gender differences in speed and depth of embodied processing. Our findings substantiate differences and communalities in social cognition mechanisms across genders and two cultures and suggest that cultural evolution or transmission should take gender as a modulating variable into account.