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

Interregional synchrony of visuomotor tracking: perturbation effects and individual differences

The present study evaluated the neural and behavioural correlates associated with a visuomotor tracking task during which a sensory perturbation was introduced that created a directional bias between moving hand and cursor position. The results revealed that trajectory error increased as a result of the perturbation in conjunction with a dynamic neural reorganization of cluster patterns that reflected distinct processing. In particular, a negatively activated cluster, characterizing the degraded information processing due to the perturbation, involved both hemispheres as well as midline area. Conversely, a positively activated cluster, indicative of compensatory processing was strongly confined to the left (dominant) hemisphere. In addition, a brain-behavioural association of good vs. poor performing participants enabled to localize a neural circuit within the left hemisphere and midline area that linked with successful performance. Overall, these data reinforce the functional significance of interregional synchrony in defining response output and behavioural success

Temporal limits on rubber hand illusion reflect individuals? temporal resolution in multisensory perception

Synchronous, but not asynchronous, multisensory stimulation has been successfully employed to manipulate the experience of body ownership, as in the case of the rubber hand illusion. Hence, it has been assumed that the rubber hand illusion is bound by the same temporal rules as in multisensory integration. However, empirical evidence of a direct link between the temporal limits on the rubber hand illusion and those on multisensory integration is still lacking. Here we provide the first comprehensive evidence that individual susceptibility to the rubber hand illusion depends upon the individual temporal resolution in multisensory perception, as indexed by the temporal binding window. In particular, in two studies we showed that the degree of temporal asynchrony necessary to prevent the induction of the rubber hand illusion depends upon the individuals? sensitivity to perceiving asynchrony during visuo-tactile stimulation. That is, the larger the temporal binding window, as inferred from a simultaneity judgment task, the higher the level of asynchrony tolerated in the rubber hand illusion. Our results suggest that current neurocognitive models of body ownership can be enriched with a temporal dimension. Moreover, our results suggest that the different aspects of body ownership operate over different time scales

Behavioral, Neural, and Computational Principles of Bodily Self-Consciousness

Recent work in human cognitive neuroscience has linked self-consciousness to the processing of multisensory bodily signals (bodily self-consciousness [BSC]) in fronto-parietal cortex and more posterior temporo-parietal regions. We highlight the behavioral, neurophysiological, neuroimaging, and computational laws that subtend BSC in humans and non-human primates. We propose that BSC includes body-centered perception (hand, face, and trunk), based on the integration of proprioceptive, vestibular, and visual bodily inputs, and involves spatio-temporal mechanisms integrating multisensory bodily stimuli within peripersonal space (PPS). We develop four major constraints of BSC (proprioception, body-related visual information, PPS, and embodiment) and argue that the fronto-parietal and temporo-parietal processing of trunk-centered multisensory signals in PPS is of particular relevance for theoretical models and simulations of BSC and eventually of self-consciousness

Interpersonal motor interactions shape multisensory representations of the peripersonal space

This perspective review focuses on the proposal that predictive multisensory integration occurring in one’s peripersonal space (PPS) supports individuals’ ability to efficiently interact with others, and that integrating sensorimotor signals from the interacting partners leads to the emergence of a shared representation of the PPS. To support this proposal, we first introduce the features of body and PPS representations that are relevant for interpersonal motor interactions. Then, we highlight the role of action planning and execution on the dynamic expansion of the PPS. We continue by presenting evidence of PPS modulations after tool use and review studies suggesting that PPS expansions may be accounted for by Bayesian sensory filtering through predictive coding. In the central section, we describe how this conceptual framework can be used to explain the mechanisms through which the PPS may be modulated by the actions of our interaction partner, in order to facilitate interpersonal coordination. Last, we discuss how this proposal may support recent evidence concerning PPS rigidity in Autism Spectrum Disorder (ASD) and its possible relationship with ASD individuals’ difficulties during interpersonal coordination. Future studies will need to clarify the mechanisms and neural underpinning of these dynamic, interpersonal modulations of the PPS

The development of multisensory integration in autism spectrum disorders

In order to understand and interact with the world, our brains must integrate information from multiple sensory modalities to create coherent representations of scenes and events. The integration of visual, tactile and proprioceptive inputs underpins the subjective sense of self and body ownership. This, in turn, underlies the development of social processes including self-awareness, imitation and empathising, which are impaired in autism spectrum disorders (ASD). Evidence suggests that the social functioning deficits characterising ASD could contribute to atypical sensory integration underlying body representation. However, the exact mechanisms underlying sensory integration difficulties have not been specified. Moreover, it is not clear when, and how, visual, tactile and proprioceptive integration matures in typical development. This is important to establish, in order to compare how and why this integration may differ in ASD populations. This thesis firstly aimed to investigate the typical development of multisensory integration underlying body representation. Experiment One found that the ability to optimally integrate visual and proprioceptive inputs during hand localisation increases with age from very little integration in 4-year-olds to almost adult-like in typically developing 10- to 11-year-olds. Experiments Two and Three showed that sensitivity to the spatial constraints of visuo-proprioceptive integration, and sensitivity to the temporal constraints of visuo-tactile integration, develops with age in 4 to 11-year-olds. Together these studies suggest that the maturation of adult-like multisensory integration for body representation follows a protracted time course over childhood. The second aim of this thesis was to investigate the evidence for two prominent theories of atypical sensory integration underlying body representation in ASD. These are 1) an over-reliance on proprioception and 2) temporally extended sensory binding. Experiment Four examined whether trypically developing (TD) adults with a high number of autistic traits exhibit an over-reliance on proprioception. No evidence was found for this, which could indicate that atypical sensory integration is only present in individuals with a clinical diagnosis of ASD. Experiments Five and Six found evidence for temporally extended visuo-tactile integration in children with ASD, compared to TD control participants. Though no evidence was found for a fundamental over-reliance on proprioception, extended binding may have led to reduced processing of temporal synchrony over modality-specific information (i.e. proprioception). Experiment Seven and Eight found no evidence of proprioceptive over-reliance or temporally extended sensory binding in adults with ASD, relative to a TD control group. I conclude that children with ASD demonstrate temporally extended visuo-tactile binding. This represents a developmental delay rather than a life-long deficit; however, it could have a life-long impact on sensory sensitivities and social processing

Balancing Interoception and Exteroception: Vestibular and Spatial Contributions to the Bodily Self

Experiencing the body as a coherent, stable, entity involves the dynamic integration of information from several internal (i.e. interoceptive) and external (i.e. exteroceptive) sensory sources, to produce a feeling that the body is mine (sense of body ownership), that I am in control (sense of agency) and I am aware of its movements (motor awareness). However, the exact contribution of these different sensory sources to self-consciousness, as well as the context in which we experience them, is still a matter of debate. This thesis aimed to investigate the neurocognitive mechanisms of body ownership, agency and motor awareness, including interoceptive (via affective touch), proprioceptive, exteroceptive (visuo-spatial) and vestibular contributions to body representation, in both healthy subjects and brain damaged patients. To examine the role of the vestibular and interoceptive systems in body ownership, a series of studies in healthy subjects was devised, using multisensory illusions (i.e. the rubber hand illusion; RHI), that involve the integration of interoceptive and exteroceptive sensory sources, and using electrical stimulation of the vestibular system (i.e. Galvanic Vestibular Stimulation; GVS). To investigate ownership, agency and motor awareness in neuropsychological patients with disorders of ownership and/or unawareness of motor deficits, behavioural manipulation of body ownership (via a rubber hand) and visual perspective (via a mirror) were tested. Finally, to explore underlying mechanisms of awareness of one’s own performance (i.e. meta-cognition), two studies were carried out in healthy subjects using behavioural manipulations of spatial reference frames (either centred on the subject, i.e. egocentric, or world-centred, i.e. allocentric). The results of these studies indicate that the vestibular system balances vision and proprioception according to contextual relevance: when there is no tactile stimulation, visual cues are stronger than proprioceptive ones (i.e. proprioceptive drifts are greater); when touch is delivered synchronously, this effect is enhanced (even more when touch is affective rather than neutral). However, when touch is only felt but not seen, the vestibular system downregulates vision in favour of proprioception (i.e. proprioceptive drifts are smaller), whilst the opposite happens when touch is only vicariously perceived via vision. Nevertheless, when the rubber hand is positioned in a non-biomechanically possible fashion, there appears to be no difference in proprioceptive drifts in comparison with anatomically plausible positions, suggesting that such rebalancing may be more related to basic multisensory integration processes underlying body representation. In patients with disorders of the self, visual cues seem to dominate over proprioceptive ones, leading to strong feelings of ownership of a rubber hand following mere exposure to it; however, the same is not true for agency, which seems to be more susceptible to changes in the environment (i.e. presence or absence of a visual feedback following attempted movement). Moreover, manipulating visual perspective using a mirror (from 1st to 3rd) seem to lead to a temporary remission of dis-ownership but not motor unawareness, suggesting that awareness may not be influenced by online changes in visual perspectives. Finally, when judging their own performance in a visuo-proprioceptive task from an egocentric rather than an allocentric perspective, healthy subjects appear less objective prospectively rather than during the task (i.e. their belief updating is biased when judging their ability to complete a task egocentrically). In sum, the work described above adds to the evidence that the sense of self derives from a complex integration of several sensory modalities, flexibly adjusting to the environment. Following brain damage, such flexibility may be impaired, even though it can be influenced by spatial perspective. Similarly, the point of reference from which we perceive stimuli affects the way we judge our own perceptual choices. Hence, the way we represent our bodily self is a dynamic process, constantly updated by exteroceptive and interoceptive incoming stimuli, regulated by the vestibular system. These findings could provide new avenues in rehabilitating disorders of the self (such as unawareness and dis-ownership)

The development of multisensory integration in autism spectrum disorders

In order to understand and interact with the world, our brains must integrate information from multiple sensory modalities to create coherent representations of scenes and events. The integration of visual, tactile and proprioceptive inputs underpins the subjective sense of self and body ownership. This, in turn, underlies the development of social processes including self-awareness, imitation and empathising, which are impaired in autism spectrum disorders (ASD). Evidence suggests that the social functioning deficits characterising ASD could contribute to atypical sensory integration underlying body representation. However, the exact mechanisms underlying sensory integration difficulties have not been specified. Moreover, it is not clear when, and how, visual, tactile and proprioceptive integration matures in typical development. This is important to establish, in order to compare how and why this integration may differ in ASD populations. This thesis firstly aimed to investigate the typical development of multisensory integration underlying body representation. Experiment One found that the ability to optimally integrate visual and proprioceptive inputs during hand localisation increases with age from very little integration in 4-year-olds to almost adult-like in typically developing 10- to 11-year-olds. Experiments Two and Three showed that sensitivity to the spatial constraints of visuo-proprioceptive integration, and sensitivity to the temporal constraints of visuo-tactile integration, develops with age in 4 to 11-year-olds. Together these studies suggest that the maturation of adult-like multisensory integration for body representation follows a protracted time course over childhood. The second aim of this thesis was to investigate the evidence for two prominent theories of atypical sensory integration underlying body representation in ASD. These are 1) an over-reliance on proprioception and 2) temporally extended sensory binding. Experiment Four examined whether trypically developing (TD) adults with a high number of autistic traits exhibit an over-reliance on proprioception. No evidence was found for this, which could indicate that atypical sensory integration is only present in individuals with a clinical diagnosis of ASD. Experiments Five and Six found evidence for temporally extended visuo-tactile integration in children with ASD, compared to TD control participants. Though no evidence was found for a fundamental over-reliance on proprioception, extended binding may have led to reduced processing of temporal synchrony over modality-specific information (i.e. proprioception). Experiment Seven and Eight found no evidence of proprioceptive over-reliance or temporally extended sensory binding in adults with ASD, relative to a TD control group. I conclude that children with ASD demonstrate temporally extended visuo-tactile binding. This represents a developmental delay rather than a life-long deficit; however, it could have a life-long impact on sensory sensitivities and social processing

Sensorimotor representation learning for an "active self" in robots: A model survey

Safe human-robot interactions require robots to be able to learn how to behave appropriately in \sout{humans' world} \rev{spaces populated by people} and thus to cope with the challenges posed by our dynamic and unstructured environment, rather than being provided a rigid set of rules for operations. In humans, these capabilities are thought to be related to our ability to perceive our body in space, sensing the location of our limbs during movement, being aware of other objects and agents, and controlling our body parts to interact with them intentionally. Toward the next generation of robots with bio-inspired capacities, in this paper, we first review the developmental processes of underlying mechanisms of these abilities: The sensory representations of body schema, peripersonal space, and the active self in humans. Second, we provide a survey of robotics models of these sensory representations and robotics models of the self; and we compare these models with the human counterparts. Finally, we analyse what is missing from these robotics models and propose a theoretical computational framework, which aims to allow the emergence of the sense of self in artificial agents by developing sensory representations through self-exploration