Quantifying Self Perception: Multisensory Temporal Asynchrony Discrimination As A Measure of Body Ownership

There are diffuse and distinct cortical networks involved in the various aspects of body representation that organize information from multiple sensory inputs and resolve conflicts when faced with incongruent situations. This coherence is typically maintained as we maneuver around the world, as our bodies change over the years, and as we gain experience. An important aspect of a congruent representation of the body in the brain is the visual perspective in which we are able to directly view our own body. There is a clear separation of the cortical networks involved in seeing our own body and that of another person. For the projects presented in my dissertation, I used an experimental design in which participants were required to make a multisensory temporal asynchrony discrimination after self-generated movements. I measured sensitivity for visual delay detection between the movement (proprioceptive, efferent and afferent information) and the visual image of that movement under differing visual, proprioceptive, and vestibular conditions. The self-advantage is a signature of body ownership and is characterized by a significantly lower threshold for delay detection for views of the body that are considered self compared to those that are regarded as other. Overall, the results from the collection of studies suggest that the tolerance for temporally matching visual, proprioceptive and efferent copy information that informs about the perceived position of body parts depends on: whether one is viewing ones own body or someone elses; the perspective in which the body is viewed; the dominant hand; and the reliability of vestibular cues which help us situate our body in space. Further, the self-advantage provides a robust measure of body ownership. The experiments provide a window on and support for the malleable nature of the representation of the body in the brain

Limb ownership and voluntary action: human behavioral and neuroimaging studies

To be able to interact with our surroundings in a goal directed manner, we need to have sense what our body is made up of as well as a sense of being able to control our body. These two experiences, the sense of body ownership and the sense of agency, respectively, are fundamental to our self-perception but have historically not received any notable attention from the scientific community. This lack of interest probably stems from the fact that these experiences are phenomenologically thin in our everyday lives and that we cannot voluntarily turn them off, they are constantly there. However, for patients suffering from disturbances in the processes underlying these experiences, their importance becomes exceedingly clear. Lesions in the frontal, temporal or parietal lobe can lead to patients losing the sense of ownership of their limb (asomatognosia), and sometimes even attributing the limb to someone else (somatoparaphrenia). Similarly, patients suffering from lesions in the frontal lobe, parietal lobe or corpus callosum can experience a lack of control over their own hand (anarchic hand syndrome), while patients suffering from schizophrenia display difficulties in distinguishing self-generated from externally generated actions, implicating disturbances in the processes underlying the sense of agency. With the discovery of body illusions, combined with functional neuroimaging, it became possible to study the perceptual and neural mechanisms of the sense of body ownership in healthy volunteers. Studies using these illusions have elucidated the perceptual rules of body ownership as well as its neural correlates and has given rise to a number of different philosophical, neurocognitive and computational models of the sense of body ownership. Meanwhile, the sense of agency has mostly been studied disconnected from the sense of body ownership, focusing on agency over self-generated external sensory effects such as auditory tones. This thesis sought to bring these two experiences together and advance our knowledge of the perceptual and neural mechanisms underlying the sense of body ownership and the sense of agency as well how these two experiences interact. Studies I & II investigate certain aspects of the sense of body ownership, and in particular its relation to the visuo-proprioceptive recalibration of limb position often seen in bodily illusions. Study III investigated how this visuo-proprioceptive recalibration is related to voluntary, but unconscious movements. Study IV investigated the neural correlates of the sense of body ownership and agency as well as their interaction. In Study I, we present empirical evidence in favor of models where the subjective sense of limb ownership is not reliant on a visuo-proprioceptive recalibration of perceived limb position. In Study II, we show that the subjective sense of limb ownership and the visuo-proprioceptive recalibration of limb position have similar temporal decay curves, suggestive of a causal relationship between them. In Study III, we show that the increase in the recalibration of limb position seen in active movements is not dependent on conscious intention, action awareness or salient error signals, indicative of an unconscious efference copy-based mechanism. Finally, in Study IV, we identify brain regions in the frontal and parietal lobe which are associated with the sense of body ownership, while brain regions in the frontal and temporal lobe are associated with the sense of agency. We show that the sense of agency in the presence of a sense of body ownership (i.e., agency of bodily actions) is associated with increased activity in the primary sensory cortex, whereas the sense of agency in the absence of ownership (i.e., agency of external events) is associated with increased activity in the visual association cortex. Together, these findings shed light on the perceptual and neural mechanisms underlying the sense of body ownership and agency as well as their interaction

Contingent sounds change the mental representation of one’s finger length

Mental body-representations are highly plastic and can be modified after brief exposure to unexpected sensory feedback. While the role of vision, touch and proprioception in shaping body-representations has been highlighted by many studies, the auditory influences on mental body-representations remain poorly understood. Changes in body-representations by the manipulation of natural sounds produced when one’s body impacts on surfaces have recently been evidenced. But will these changes also occur with non-naturalistic sounds, which provide no information about the impact produced by or on the body? Drawing on the well-documented capacity of dynamic changes in pitch to elicit impressions of motion along the vertical plane and of changes in object size, we asked participants to pull on their right index fingertip with their left hand while they were presented with brief sounds of rising, falling or constant pitches, and in the absence of visual information of their hands. Results show an “auditory Pinocchio” effect, with participants feeling and estimating their finger to be longer after the rising pitch condition. These results provide the first evidence that sounds that are not indicative of veridical movement, such as non-naturalistic sounds, can induce a Pinocchio-like change in body-representation when arbitrarily paired with a bodily action

A Ilusão da Mão de Borracha: Evidências de Integração Multissensorial da Propriocepção

The present review aims to describe the consolidation of a multisensory integration hypothesis for proprioception through the description of different Rubber Hand Illusion (RHI) experimental settings. RHI is a paradigm created in 1998 to explore the relation between visual and tactile sensory systems. The task involves a synchronous stroking, using a paintbrush, of one of the subjects hand, occluded from his vision, and a prosthetic rubber hand located in front of the subject. Instructed to look at the rubber hand, after approximately half a minute, the subject starts to feel as if the rubber hand is his own hand. The illusion produces a feeling of ownership of the rubber hand. Scientific research has widely investigated the experiment in the last 15 years, indicating the dynamic functions of the brain and body sensory systems, as well as shedding light on amputee rehabilitation and different types of paresthesia The review is structured around three topics: 1) the definition of the RHI, its limits and scope, 2) the physiological and neurocognitive evidence backing the RHI, and 3) the use of RHI in action experimental settings. The paper concludes that RHI is a convenient example of a neuroscientific trend towards an integrated account of body, brain and perceptual space. The illusion has also established an alternative way for studying proprioception and related brain dynamics in normal subjects.    La presente revisión tiene como objetivo describir una hipótesis de integración multisensorial para la propiocepción a través de la descripción de distintos configuraciones experimentales con la Ilusión de la Mano de Goma (img). img es un paradigma creado en 1998 para explorar la relación entre los sistemas sensoriales visual y táctil. La tarea implica una estimulación síncrona de una mano de los sujetos, oculto de su visión, y una mano de goma en frente del sujeto. Instruidos para mirar la mano de goma, después de aproximadamente medio minuto, el sujeto comienza a sentir la mano de goma como su propia mano. La ilusión produce un sentimiento de propiedad de la mano de goma. La literatura ha investigado ampliamente el experimento en los últimos 15 años, demostrando las funciones dinámicas de los sistemas sensoriales del cerebro y del cuerpo, así como clarificando aspectos de la rehabilitación de sujetos amputados y diferentes tipos de parestesia. La revisión se estructura en torno de tres temas: (1) definición de la img, sus límites y alcances, (2) evidencias fisiológicas y neurocognitivas que dan apoyo a la img, y (3) la img en configuraciones experimentales implicando acción. La revisión concluye que la img es un ejemplo práctico de una tendencia neurocientífica innovadora para el estudio integrado del cuerpo, el cerebro y el espacio perceptual. La ilusión también ha establecido una forma alternativa para el estudio de la propiocepción y la dinámica del cerebro en sujetos normalesA presente revisão tem como objetivo descrever uma hipótese de integração multissensorial para a propriocepção através da descrição de diferentes configurações experimentais com a Ilusão da Mão de Borracha (img). img é um paradigma criado em 1998 para explorar a relação entre os sistemas sensoriais visual e táctil. A tarefa implica uma estimulação síncrona de uma mão dos sujeitos, oculto de sua visão, e uma mão de borracha em frente ao sujeito. Instruídos para olhar a mão de borracha, depois de aproximadamente meio minuto, o sujeito começa a sentir a mão de borracha como a sua própria mão. A ilusão produz um sentimento de propriedade da mão de borracha. A literatura tem investigado amplamente o experimento nos últimos 15 anos, demostrando as funções demonstrando as funções dinâmicas dos sistemas sensoriais do cérebro e do corpo, assim como clarificando aspetos da reabilitação de sujeitos amputados e diferentes tipos de parestesia. A revisão estrutura-se em torno a três temas: (1) definição da img, os seus limites e alcances, (2) evidências fisiológicas e neurocognitivas que dão apoio à img e (3) a img em configurações experimentais implicando ação. A revisão conclui que a img é um exemplo prático de uma tendência neurocientífica inovadora para o estudo integrado do corpo, o cérebro e o espaço percetual. A ilusão também tem estabelecido uma alternativa para o estudo da propriocepção e a dinâmica do cérebro em sujeitos normais

Ownership and Agency of an Independent Supernumerary Hand Induced by an Imitation Brain-Computer Interface

To study body ownership and control, illusions that elicit these feelings in non-body objects are widely used. Classically introduced with the Rubber Hand Illusion, these illusions have been replicated more recently in virtual reality and by using brain-computer interfaces. Traditionally these illusions investigate the replacement of a body part by an artificial counterpart, however as brain-computer interface research develops it offers us the possibility to explore the case where non-body objects are controlled in addition to movements of our own limbs. Therefore we propose a new illusion designed to test the feeling of ownership and control of an independent supernumerary hand. Subjects are under the impression they control a virtual reality hand via a brain-computer interface, but in reality there is no causal connection between brain activity and virtual hand movement but correct movements are observed with 80% probability. These imitation brain-computer interface trials are interspersed with movements in both the subjects' real hands, which are in view throughout the experiment. We show that subjects develop strong feelings of ownership and control over the third hand, despite only receiving visual feedback with no causal link to the actual brain signals. Our illusion is crucially different from previously reported studies as we demonstrate independent ownership and control of the third hand without loss of ownership in the real hands

Where Are Your Fingers?

How do we know how our fingers are oriented in space? Contributions to limb and finger perception include afferent sensory signals from the muscles, joints, skin, as well as vision and other senses, and top-down assumptions about the bodys dimensions. A growing body of literature has examined the perception of finger and hand position and dimensions in a bid to understand how the limbs are represented in the brain. However, no studies have examined perception of the orientation of the fingers. A comprehensive model of highly articulated body parts must include perception of their orientation as well as their position. This dissertation seeks to fill an existing gap in the literature by exploring contributions to finger orientation perception, using a novel line-matching task. In Chapter 3 I provide evidence that vestibular disruption using galvanic vestibular stimulation (GVS) leads to an inward rotation of perceived finger orientation, and provide some evidence that finger orientation perception may not be accurate at baseline. In Chapter 4 I show that left- and right-handers may have differ- ent strategies for finger orientation perception, and provide evidence for an outward rotational bias that increases as the hands are placed further laterally from the body midline. In Chapter 5, I show that the way the probe line is initially displayed has a significant impact on performance, specifically on asymmetries of responses for the two hands and the compression of responses across the test range. I further show that the outward bias observed in Chapter 4 might be due to order of hand placement and differences in muscle strain across conditions. In Chapters 6 and 7, I show no difference in orientation perception for the ring and index fingers, but find an overall inward rotation of orientation estimates for palm-down hand postures, compared to palm-up postures. My research clearly shows that perceived finger orientation, as measured in my line-matching paradigm, is highly context-dependent. I discuss this in the greater context of the limb perception literature and outline some of the questions which much still be addressed in order to arrive at a comprehensive model of hand and finger perception

Touching on elements for a non-invasive sensory feedback system for use in a prosthetic hand

Hand amputation results in the loss of motor and sensory functions, impacting activities of daily life and quality of life. Commercially available prosthetic hands restore the motor function but lack sensory feedback, which is crucial to receive information about the prosthesis state in real-time when interacting with the external environment. As a supplement to the missing sensory feedback, the amputee needs to rely on visual and audio cues to operate the prosthetic hand, which can be mentally demanding. This thesis revolves around finding potential solutions to contribute to an intuitive non-invasive sensory feedback system that could be cognitively less burdensome and enhance the sense of embodiment (the feeling that an artificial limb belongs to one’s own body), increasing acceptance of wearing a prosthesis.A sensory feedback system contains sensors to detect signals applied to the prosthetics. The signals are encoded via signal processing to resemble the detected sensation delivered by actuators on the skin. There is a challenge in implementing commercial sensors in a prosthetic finger. Due to the prosthetic finger’s curvature and the fact that some prosthetic hands use a covering rubber glove, the sensor response would be inaccurate. This thesis shows that a pneumatic touch sensor integrated into a rubber glove eliminates these errors. This sensor provides a consistent reading independent of the incident angle of stimulus, has a sensitivity of 0.82 kPa/N, a hysteresis error of 2.39±0.17%, and a linearity error of 2.95±0.40%.For intuitive tactile stimulation, it has been suggested that the feedback stimulus should be modality-matched with the intention to provide a sensation that can be easily associated with the real touch on the prosthetic hand, e.g., pressure on the prosthetic finger should provide pressure on the residual limb. A stimulus should also be spatially matched (e.g., position, size, and shape). Electrotactile stimulation has the ability to provide various sensations due to it having several adjustable parameters. Therefore, this type of stimulus is a good candidate for discrimination of textures. A microphone can detect texture-elicited vibrations to be processed, and by varying, e.g., the median frequency of the electrical stimulation, the signal can be presented on the skin. Participants in a study using electrotactile feedback showed a median accuracy of 85% in differentiating between four textures.During active exploration, electrotactile and vibrotactile feedback provide spatially matched modality stimulations, providing continuous feedback and providing a displaced sensation or a sensation dispatched on a larger area. Evaluating commonly used stimulation modalities using the Rubber Hand Illusion, modalities which resemble the intended sensation provide a more vivid illusion of ownership for the rubber hand.For a potentially more intuitive sensory feedback, the stimulation can be somatotopically matched, where the stimulus is experienced as being applied on a site corresponding to their missing hand. This is possible for amputees who experience referred sensation on their residual stump. However, not all amputees experience referred sensations. Nonetheless, after a structured training period, it is possible to learn to associate touch with specific fingers, and the effect persisted after two weeks. This effect was evaluated on participants with intact limbs, so it remains to evaluate this effect for amputees.In conclusion, this thesis proposes suggestions on sensory feedback systems that could be helpful in future prosthetic hands to (1) reduce their complexity and (2) enhance the sense of body ownership to enhance the overall sense of embodiment as an addition to an intuitive control system

The embodied user : corporeal awareness & media technology

Human beings are proficient users of tools and technology. At times, our interactions with a technological artifact appear so effortless, that the distinction between the artifact and the body starts to fade. When operating anthropomorphically designed teleoperation systems, for example, some people develop the vivid experience that they are physically there at the remote site (i.e., telepresence). Others might even come to sense the slave robot’s arms and hands as their own. The process in which the central nervous system categorizes an object as a part of the body, and in which a discrimination is made between what is contained within and outside the bodily boundaries, is called self-attribution. The aim of this thesis is twofold: (a) To determine the personal factors (e.g., the characteristics of an individual’s psychological makeup) and situational factors (e.g., the appearance of objects) that constrain or facilitate self-attribution, and (b) to determine the degree to which these factors affect people’s experiences with media technology. In Chapter 2, we describe the theoretical framework of our research which is centered on a conception of the user of technology as an embodied agent. In this chapter we distinguish two important, but often confused aspects of embodiment: the body schema, and the body image. The body schema is defined as a dynamic distributed network of procedures aimed at guiding behavior. In contrast, we defined the body image as a part of the process of consciousness and, thus, as consisting of those higher-order discriminations (or qualia) that pertain to the body, and one’s self-perception thereof. To investigate the individual and situational factors that constrain or facilitate selfattribution (i.e., incorporation into the body image), we employ the experimental paradigm of the rubber-hand illusion (Botvinick & Cohen, 1998). In this illusion, which is induced by stroking a person’s concealed hand together with a visible fake one, some people start to sense the fake hand as an actual part of their body. In Chapter 3, we investigate the rubberhand illusion under two mediated conditions: (1) a virtual reality condition, where both the fake hand and its stimulation were projected on the table in front of the participant, and (2) a mixed reality condition, where the fake hand was projected, but its stimulation was unmediated. Our experiment reveals that people can develop the rubber-hand illusion under mediated conditions, but the resulting illusion may, depending on the technology used, be less vivid than in the traditional unmediated setup. In Chapter 4, we investigate the extent to which visual discrepancies between the foreign object and a human hand affect people in developing a vivid rubber-hand illusion. We found that people experience a more vivid illusion when the foreign object resembles the human hand in terms of both shape and texture. Taken together, the experiments in Chapters 3 and 4 support the view that the rubber-hand illusion is not merely governed by a bottom-up process (i.e., based on visuotactile integration), but is affected, top-down, by a cognitive representation of what the human body is like (e.g., Tsakiris and Haggard, 2005). In the rubber-hand illusion, people commonly misperceive the location of their concealed hand toward the direction of the fake hand (Tsakiris & Haggard, 2005). As such, this so-called proprioceptive drift is often used as an alternative to self-reports in assessing the vividness of the illusion (e.g., Tsakiris & Haggard, 2005). In Chapter 5, we investigate the extent to which the observed shift in felt position of the concealed hand can be attributed to experiencing the illusion. For this purpose, we test how various features of the experimental setup of the rubber-hand illusion, which in themselves are not sufficient to elicit the illusion, affect proprioceptive drift. We corroborate existing research which demonstrates that looking at a fake hand or a tabletop for five minutes, in absence of visuotactile stimulation, is sufficient to induce a change in the felt position of an unseen hand (e.g., Gross et al., 1974). Moreover, our experiments indicate that the use of proprioceptive drift as a measure for the strength of the rubber-hand illusion yields different conclusions than an assessment by means of self-reports. Based on these results, we question the validity of proprioceptive drift as an alternative measure of the vividness of the rubber-hand illusion. In Chapter 6, we propose and test a model of the vividness of the rubber-hand illusion. In two experiments, we successfully modeled people’s self-reported experiences related to the illusion (e.g., "the fake hand felt as my own") based on three estimates: (a) a person’s susceptibility for the rubber-hand illusion, (b) the processing demand that is required for a particular experience, and (c) the suppression/constraints imposed by the situation. We demonstrate that the impressions related to the rubber-hand illusion, and by inference the processes behind them, are comparable for different persons. This is a non-trivial finding as such invariance is required for an objective scaling of individual susceptibility and situational impediment on the basis of self-reported experiences. Regarding the validity of our vividness model, we confirm that asynchrony (e.g., Botvinick & Cohen, 1998) and information-poor stimulation (e.g., Armel & Ramachandran, 2003) constrain the development of a vivid rubber-hand illusion. Moreover, we demonstrate that the correlation between a person’s susceptibility for the rubber-hand illusion and the extent of his of her proprioceptive drift is fairly moderate, thereby confirming our conclusions from Chapter 5 regarding the limited validity of proprioceptive drift as a measure of the vividness of the rubber-hand illusion. In Chapter 7, we investigate the extent to which the large individual differences in people’s susceptibility for the illusion can be explained by body image instability, and the ability to engage in motor imagery of the hand (i.e., in mental own hand transformations). In addition, we investigate whether the vividness of the illusion is dependent on the anatomical implausibility of the fake hand’s orientation. With respect to body image instability, we corroborate a small, but significant, correlation between susceptibility and body image aberration scores: As expected, people with a more unstable body image are also more susceptible to the rubber-hand illusion (cf. Burrack & Brugger, 2005). With respect to the position and orientation of the fake hand on the table, we demonstrate that people experience a less vivid rubber-hand illusion when the fake hand is orientated in an anatomically impossible, as compared to an anatomically possible manner. This finding suggests that the attribution of foreign objects to the self is constrained by the morphological capabilities of the human body. With respect to motor imagery, our results indicate a small, but significant, correlation between susceptibility and response times to a speeded left and right hands identification task. In other words, people who are more attuned to engage in mental own hand transformations are also better equipped to develop vivid rubber-hand illusions. In Chapter 8, we examine the role of self-attribution in the experience of telepresence. For this purpose, we introduce the technological domain of mediated social touch (i.e., interpersonal touching over a distance). We anticipated that, compared to a morphologically incongruent input medium, a morphologically congruent medium would be more easily attributed to the self. As a result, we expected our participants to develop a stronger sense of telepresence when they could see their interaction partner performing the touches on a sensor-equipped mannequin as opposed to a touch screen. Our participants, as expected, reported higher levels of telepresence, and demonstrated more physiological arousal with the mannequin input medium. At the same time, our experiment revealed that these effects might not have resulted from self-attribution, and thus that other psychological mechanisms of identification might play a role in telepresence experiences. In Chapter 9, the epilogue, we discuss the main contributions and limitations of this thesis, while taking a broader perspective on the field of research on media technologies and corporeal awareness