The Empathy Quotient (EQ) predicts perceived strength of bodily illusions and illusion-related sensations of pain

In this study we test the possible implications of high empathising skills on bodily self–other distinction by measuring the strength of a body ownership illusion and a related experience of illusory pain. One-hundred adult participants completed the Empathy Quotient (EQ) questionnaire. Twenty participants from the top quintile and 20 participants from the bottom quintile of the EQ distribution took part in a laboratory experiment. In the experiment, a classical Rubber Hand Illusion (RHI) was induced followed by the presentation of a series of painful stimuli to the rubber hand. Participants were asked to self-rate the strength of their subjective experience of the RHI and of the illusory pain. A proprioceptive location judgment on the position of the hidden hand was also required before and after RHI induction, to record drifts towards the rubber hand. We found a significant difference between high- and low-empathy participants in RHI and pain score. The EQ was not related with the proprioceptive location judgement drift. It thus appears to be a better predictor of subjective ownership feelings and phenomenological self–other merging than of the behavioural components of bodily illusions.     

我观故我在？— 从橡胶手错觉对自我身体所有权的探讨

橡胶手错觉是一种能将非自我的肢体感知为自我的肢体的反应。继发现橡胶手错觉现象后,研究者通过操纵自变量以及观测不同的因变量,得到了大量新的研究结果。橡胶手错觉的出现与强度受到时间、空间和手姿势的影响。橡胶手错觉的产生机制为单纯的多感觉整合或多感觉整合与身体表征共同作用的结果。未来研究侧重于被试取样、研究策略以及医学领域中瘫痪患者的认知神经康复和截肢病人的假肢控制方面。     

Visual information and rubber hand embodiment differentially affect reach-to-grasp actions

During the “rubber hand illusion” (RHI) participants feel touch originating from an artificial hand, which is felt to belong to the own body. The perceived location of the real hand is shifted towards the location of the artificial hand. However, evidence as to whether the RHI is accompanied by alterations of hand action is mixed. We found that the perceived size of one's own hand was affected by the size of the artificial hand that was used to elicit the illusion. Moreover, we tested a possible transfer of the RHI to a reach-to-grasp action. We observed that hand transport (i.e., reach) errors after RHI induction were independent of artificial hand size, showing that the parameter which is important for these reaching errors is the hand's perceived location. Results thus show that the RHI affects not only perceptual, but also action processing. In contrast, grip aperture was affected by artificial hand size independent of the RHI, suggesting that visual information about hand size affects grasping independent of embodiment of the artificial hand. Grip size increased with artificial hand size; this effect is explained by a higher reliance on proprioceptive information during blind reaching after receiving distorted visual information.     

Hearing visuo‐tactile synchrony – Sound‐induced proprioceptive drift in the invisible hand illusion

The rubber hand illusion (RHI) and its variant the invisible hand illusion (IHI) are useful for investigating multisensory aspects of bodily self‐consciousness. Here, we explored whether auditory conditioning during an RHI could enhance the trisensory visuo‐tactile‐proprioceptive interaction underlying the IHI. Our paradigm comprised of an IHI session that was followed by an RHI session and another IHI session. The IHI sessions had two parts presented in counterbalanced order. One part was conducted in silence, whereas the other part was conducted on the backdrop of metronome beats that occurred in synchrony with the brush movements used for the induction of the illusion. In a first experiment, the RHI session also involved metronome beats and was aimed at creating an associative memory between the brush stroking of a rubber hand and the sounds. An analysis of IHI sessions showed that the participants’ perceived hand position drifted more towards the body‐midline in the metronome relative to the silent condition without any sound‐related session differences. Thus, the sounds, but not the auditory RHI conditioning, influenced the IHI. In a second experiment, the RHI session was conducted without metronome beats. This confirmed the conditioning‐independent presence of sound‐induced proprioceptive drift in the IHI. Together, these findings show that the influence of visuo‐tactile integration on proprioceptive updating is modifiable by irrelevant auditory cues merely through the temporal correspondence between the visuo‐tactile and auditory events.     

Having a body versus moving your body: How agency structures body-ownership

We investigated how motor agency in the voluntary control of body movement influences body awareness. In the Rubber Hand Illusion (RHI), synchronous tactile stimulation of a rubber hand and the participant's hand leads to a feeling of the rubber hand being incorporated in the participant's own body. One quantifiable behavioural correlate of the illusion is an induced shift in the perceived location of the participant's hand towards the rubber hand. Previous studies showed that the induced changes in body awareness are local and fragmented: the proprioceptive drift is largely restricted to the stimulated finger. In the present study, we investigated whether active and passive movements, rather than tactile stimulation, would lead to similarly fragmented body awareness. Participants watched a projected image of their hand under three conditions: active finger movement, passive finger movement, and tactile stimulation. Visual feedback was either synchronous or asynchronous with respect to stimulation of the hand. A significant overall RHI, defined as greater drifts following synchronous than asynchronous stimulation, was found in all cases. However, the distribution of the RHI across stimulated and non-stimulated fingers depended on the kind of stimulation. Localised proprioceptive drifts, specific to the stimulated finger, were found for tactile and passive stimulation. Conversely, during active movement of a single digit, the proprioceptive drifts were not localised to that digit, but were spread across the whole hand. Whereas a purely proprioceptive sense of body-ownership is local and fragmented, the motor sense of agency integrates distinct body-parts into a coherent, unified awareness of the body.     

Susceptibility to the rubber hand illusion does not tell the whole body-awareness story

The rubber hand illusion (RHI) is an enigmatic illusion that creates a feeling of owning an artificial limb. Enthusiasts of this paradigm assert that it operationalizes bodily self-awareness, but there are reasons to doubt such a clear link. Because little is known about other functional contributions to the RHI, including effects of context-dependent visual processing and cognitive control or the ability to resolve intermodal conflict, we carried out two complementary experiments. In the first, we examined the relationships between the RHI and (1) body awareness, as assessed by the Body Perception Questionnaire (BPQ); (2) context-dependent visual processing, as assessed by the rod-and-frame test (RFT); and (3) conflict resolution, as assessed by the Stroop test. We found a significant positive correlation between the RHI-associated proprioceptive drift and context-dependent visual processing on the RFT, but not between the RHI and body awareness on the BPQ. In the second experiment, we examined the RHI in advanced yoga practitioners with an embodied lifestyle and a heightened sense of their own body in space. They succumbed to the illusion just as much as did yoga-naïve control participants, despite significantly greater body awareness on the BPQ. These findings suggest that susceptibility to the RHI and awareness of one’s own body are at least partially independent processes.     

The Rubber Hand Illusion: two's a company, but three's a crowd

On the one hand, it is often assumed that the Rubber Hand Illusion (RHI) is constrained by a structural body model so that one cannot implement supernumerary limbs. On the other hand, several recent studies reported illusory duplication of the right hand in subjects exposed to two adjacent rubber hands. The present study tested whether spatial constraints may affect the possibility of inducing the sense of ownership to two rubber hands located side by side to the left of the subject's hand. We found that only the closest rubber hand appeared both objectively (proprioceptive drift) and subjectively (ownership rating) embodied. Crucially, synchronous touch of a second, but farther, rubber hand disrupted the objective measure of the RHI, but not the subjective one. We concluded that, in order to elicit a genuine RHI for multiple rubber hands, the two rubber hands must be at the same distance from the subject's hand/body.     

Affective touch modulates the rubber hand illusion

Introduction

Humans experience touch as pleasant when this occurs with a certain velocity (1–10cm/s). Affective, pleasant touch is thought to be mediated by a distinct neural pathway consisting of un-myelinated tactile afferents (C tactile fibers) that respond to stroking with a low velocity on the hairy skin. As pleasant touch provides additional information on bodily signals we hypothesized that, compared to regular touch, pleasant touch would have a stronger effect on body ownership as measured through induction of the rubber hand illusion (RHI).

Methods

Two experiments involving the RHI were conducted. In the first experiment, the effects of stroking velocity (3 cm/s and 30 cm/s) and stroking material (soft/rough) on the RHI were tested. In the second experiment, the effect of an additional stroking velocity (0.3 cm/s) and side of stimulation (hairy and glabrous) was examined.

Results

The first experiment showed that low velocity stroking in combination with a soft material was not only regarded as most pleasant but also resulted in an enhanced RHI on proprioceptive drift and temperature measurements. In the second experiment, we confirmed that stroking with a velocity of 3 cm/s resulted in a larger RHI in terms of proprioceptive drift. In addition, compared to regular touch, pleasant touch of the hairy skin resulted in a larger proprioceptive drift, while similar stroking on the glabrous side of the skin did not induce a stronger effect of RHI on proprioceptive drift.

Conclusion

Our data suggest that pleasant touch modulates the body representation which is consistently reflected in a larger proprioceptive drift. Our data also suggest that C tactile fibers are likely to be involved in the modulation of body ownership.     

Anatomically plausible illusory posture affects mental rotation of body parts

During mental rotation (MR) of body parts, people internally simulate the movement of their corresponding body segments. These sensory–motor mechanisms render MR sensitive to proprioceptive information (e.g., posture). Similar mechanisms can alter illusory hand ownership following synchronous visuotactile stimulation (e.g., the rubber hand illusion [RHI]). In the present study, we first showed that illusory ownership for a fake hand can also be induced when the posture of the fake hand (palm-up) does not correspond with the subject’s physical hand posture (palm-down). Then we tested whether illusory ownership for a fake hand in such a posture impacts the MR of hands carried out immediately and repeatedly after the RHI. The results showed that MR was altered for the view corresponding to the fake hand’s posture, but not for other views. Additionally, these effects depended on illusory ownership, as only synchronous visuotactile stimulation was found to lead to these changes, characterized by a modulation of the rotation-dependent profile of MR response times. These findings show that similar sensory–motor mechanisms are recruited during the MR of hands and illusory hand ownership manipulated through multisensory mismatch, and that bottom-up visuotactile stimulation interferes with high-level imagery processes.     

The spatial distance rule in the moving and classical rubber hand illusions

The rubber hand illusion (RHI) is a perceptual illusion in which participants perceive a model hand as part of their own body. Here, through the use of one questionnaire experiment and two proprioceptive drift experiments, we investigated the effect of distance (12, 27.5, and 43 cm) in the vertical plane on both the moving and classical RHI. In both versions of the illusion, we found an effect of distance on ownership of the rubber hand for both measures tested. Our results further suggested that the moving RHI might follow a narrower spatial rule. Finally, whereas ownership of the moving rubber hand was affected by distance, this was not the case for agency, which was present at all distances tested. In sum, the present results generalize the spatial distance rule in terms of ownership to the vertical plane of space and demonstrate that also the moving RHI obeys this rule.     

What is embodiment? A psychometric approach

What is it like to have a body? The present study takes a psychometric approach to this question. We collected structured introspective reports of the rubber hand illusion, to systematically investigate the structure of bodily self-consciousness. Participants observed a rubber hand that was stroked either synchronously or asynchronously with their own hand and then made proprioceptive judgments of the location of their own hand and used Likert scales to rate their agreement or disagreement with 27 statements relating to their subjective experience of the illusion. Principal components analysis of this data revealed four major components of the experience across conditions, which we interpret as: embodiment of rubber hand, loss of own hand, movement, and affect. In the asynchronous condition, an additional fifth component, deafference, was found. Secondary analysis of the embodiment of runner hand component revealed three subcomponents in both conditions: ownership, location, and agency. The ownership and location components were independent significant predictors of proprioceptive biases induced by the illusion. These results suggest that psychometric tools may provide a rich method for studying the structure of conscious experience, and point the way towards an empirically rigorous phenomenology.     

The rubber hand illusion revisited: visuotactile integration and self-attribution

Watching a rubber hand being stroked, while one's own unseen hand is synchronously stroked, may cause the rubber hand to be attributed to one's own body, to "feel like it's my hand." A behavioral measure of the rubber hand illusion (RHI) is a drift of the perceived position of one's own hand toward the rubber hand. The authors investigated (a) the influence of general body scheme representations on the RHI in Experiments 1 and 2 and (b) the necessary conditions of visuotactile stimulation underlying the RHI in Experiments 3 and 4. Overall, the results suggest that at the level of the process underlying the build up of the RHI, bottom-up processes of visuotactile correlation drive the illusion as a necessary, but not sufficient, condition. Conversely, at the level of the phenomenological content, the illusion is modulated by top-down influences originating from the representation of one's own body.     

Self awareness and the body image

What mental representations give us the sense of our body as a unique object in the world? We investigated this issue in the context of the rubber hand illusion (RHI), an illusion of body image in which a prosthetic hand brushed synchronously, but not asynchronously, with one’s own hand is perceived as actually being one’s hand. We conducted a large-scale study of the RHI, and used psychometric analysis to reveal the structure of the subjective experience of embodiment [Longo et al. (2008). What is embodiment? A psychometric approach. Cognition,107, 978-998]. Here, we use this dataset to investigate the relation between incorporation of a rubber hand into the body image and the perceived similarity between the participant’s hand and the rubber hand. Objective similarity (as measured by skin luminance, hand shape, and third-person similarity ratings) did not appear to influence participants’ experience of the RHI. Conversely, incorporation of the rubber hand into the body image did affect the similarity that participants perceived between their own hand and the rubber hand. Participants who had experienced the RHI perceived their hand and the rubber hand as significantly more similar than participants who had not experienced the illusion. That is, embodiment leads to perceived similarity, but perceived similarity does not lead to embodiment. Furthermore, similarity ratings following the illusion were selectively correlated with some components of embodiment, but not with others. These results suggest an important role of a mental body image in the perception of the relation between the self and others.     

Bodily Awareness, Imagination and the Self

Common wisdom tells us that we have five senses: sight, hearing, smell, taste and touch. These senses provide us with a means of gaining information concerning objects in the world around us, including our own bodies. But in addition to these five senses, each of us is aware of our own body in ways in which we are aware of no other thing. These ways include our awareness of the position, orientation, movement, and size of our limbs (proprioception and kinaesthesia), our sense of balance, and our awareness of bodily sensations such as pains, tickles, and sensations of pressure or temperature. We can group these together under the title ‘bodily awareness’. The legitimacy of grouping together these ways of gaining information is shown by the fact that they are unified phenomenologically; they provide the subject with an awareness of his or her body ‘from the inside’. Bodily awareness is an awareness of our own bodies from within. This perspective on our own bodies does not, cannot, vary. As Merleau‐Ponty writes, ‘my own body…is always presented to me from the same angle’ (1962: 90). It has recently been claimed by a number of philosophers that, in bodily awareness, one is not simply aware of one's body as one's body, but one is aware of one's body as oneself. That is, when I attend to the object of bodily awareness I am presented not just with my body, but with my ‘bodily self’. The contention of the present paper is that such a view is misguided. In the first section I clarify just what is at issue here. In the remainder of the paper I present an argument, based on two claims about the nature of the imagination, against the view that the bodily self is presented in bodily awareness. Section two defends the dependency thesis; a claim about the relation between perception and sensory imagination. Section three defends a certain view about our capacity to imagine being other people. Section four presents the main argument against the bodily self awareness view and section five addresses some objections.     

How do objective and subjective career success interrelate over time?

The present research is concerned with the direction of influence between objective and subjective career success. We conducted a prospective longitudinal study with five waves of measurement that covered a time span of 10 years. Participants were professionals working in different occupational fields (N=1,336). We modelled the changes in objective success (income, hierarchical position), in other‐referent subjective success (subjective success as compared to a reference group), and in self‐referent subjective success (job satisfaction) by means of latent growth curve analysis. Objective success influenced both the initial level and the growth of other‐referent subjective success, but it had no influence on job satisfaction. Most importantly, both measures of subjective success and both their initial levels and their changes had strong influences on the growth of objective success. We conclude that the ‘objective success influences subjective success’ relationship is smaller than might be expected, whereas the ‘subjective success influences objective success’ relationship is larger than might be expected.     

The rubber hand illusion in a mirror

In the rubber hand illusion (RHI) one’s hand is hidden, and a fake hand is visible. We explored the situation in which visual information was available indirectly in a mirror. In the mirror condition, compared to the standard condition (fake hand visible directly), we found no reduction of the RHI following synchronised stimulation, as measured by crossmanual pointing and by a questionnaire. We replicated the finding with a smaller mirror that prevented visibility of the face. The RHI was eliminated when a wooden block replaced the fake hand, or when the hand belonged to another person or mannequin. We conclude that awareness of the reflection is the critical variable, despite the distant visual localisation of the hand in a mirror and the third-person perspective. Stimuli seen in a mirror activate the same response as stimuli seen in peripersonal space, through knowledge that they are near one’s body.     

Reflexivity,Subjectivity, and the Constructed Self: A Buddhist Model

The aim of this article is to take up three closely connected questions. First, does consciousness essentially involve subjectivity? Second, what is the connection, if any, between pre-reflective self-consciousness and subjectivity? And, third, does consciousness necessarily involve an ego or self? I will draw on the Yogācāra–Madhyamaka synthesis of ?āntarak?ita (eighth century common era) to develop an account of the relation between consciousness, subjectivity, and the self. I will argue, first, that phenomenal consciousness is reflexive or self-illuminating (svaprakā?ya). Second, I will argue that consciousness necessarily involves minimal subjectivity. Third, I will argue that neither the reflexivity nor the subjectivity of consciousness implies that there is any entity such as the self or ego over and above reflexive consciousness. Fourth, I will argue that what we normally think of as ‘the self’ is best understood as a complex, multi-layered process (aha?kāra, ‘I-making’) that emerges within the pre-egoic flow of subjective consciousness.     

Development of allocentric spatial recall from new viewpoints in virtual reality

Using landmarks and other scene features to recall locations from new viewpoints is a critical skill in spatial cognition. In an immersive virtual reality task, we asked children 3.5–4.5 years old to remember the location of a target using various cues. On some trials they could use information from their own self‐motion. On some trials they could use a view match. In the very hardest kind of trial, they were ‘teleported’ to a new viewpoint and could only use an allocentric spatial representation. This approach provides a strict test for allocentric coding (without either a matching viewpoint or self‐motion information) while avoiding additional task demands in previous studies (it does not require them to deal with a small table‐top environment or to manage stronger cue conflicts). Both the younger and older groups were able to point back at the target location better than chance when they could use view matching and/or self‐motion, but allocentric recall was only seen in the older group (4.0–4.5). In addition, we only obtained evidence for a specific kind of allocentric recall in the older group: they tracked one major axis of the space significantly above chance, r(158) = .28, but not the other, r(158) = ?.01. We conclude that there is a major qualitative change in coding for spatial recall around the fourth birthday, potentially followed by further development towards fully flexible recall from new viewpoints.     

Application of the rubber hand illusion paradigm: comparison between upper and lower limbs

The “rubber hand illusion (RHI)” is a perceptual illusion, which allows the integration of artificial limbs into the body representation of a person by means of combined visual and tactile stimulation. The illusion has been frequently replicated but always concerning the upper limbs. The present study verified an analog illusion that can be called the “rubber foot illusion” (RFI). In a conjoint experiment using both a rubber hand and a rubber foot, brushstrokes were applied to the respective real and rubber limb placed alongside the real one. However, only the artificial limb’s handling was visible. The brushstrokes were given either synchronously, with a delay of ±0.5 s, or without tactile stimulation of the real limb. Questionnaire data and the proprioceptive drift towards the rubber limb (determined by calling on the subjects to show where they locate their unseen limb) defined the illusion strength. Results revealed that the illusion was induced in both limbs with comparable strength, but only in the synchronous condition.