Gaetano Tieri

Mere observation of body discontinuity affects perceived ownership and vicarious agency over a virtual hand

The mental representation of one’s body typically implies the continuity of its parts. Here, we used immersive virtual reality to explore whether mere observation of visual discontinuity between the hand and limb of an avatar could influence a person’s sense of ownership of the virtual body (feeling of ownership, FO) and being the agent of its actions (vicarious agency, VA). In experiment 1, we tested whether placing different amounts of visual discontinuity between a virtual hand and limb differently modulate the perceived FO and VA. Participants passively observed from a first-person perspective four different versions of a virtual limb: (1) a full limb; a hand detached from the proximal part of the limb because of deletion of (2) the wrist; (3) the wrist and forearm; (4) and the wrist, forearm and elbow. After observing the static or moving virtual limb, participants reported their feeling of ownership (FO) and vicarious agency (VA) over the hand. We found that even a small visual discontinuity between the virtual hand and arm significantly decreased participants’ FO over the hand during observation of the static limb. Moreover, in the same condition, we found that passive observation of the avatar’s actions induced a decrease in both FO and VA. We replicated the same results in a second study (experiment 2) where we investigated the modulation of FO and VA by comparing the visual body discontinuity with a condition in which the virtual limb was partially occluded. Our data show that mere observation of limb discontinuity can change a person’s ownership and agency over a virtual body observed from a first-person perspective, even in the absence of any multisensory stimulation of the real body. These results shed new light on the role of body visual continuity in modulating self-awareness and agency in immersive virtual reality.

Body visual discontinuity affects feeling of ownership and skin conductance responses.

When we look at our hands we are immediately aware that they belong to us and we rarely doubt about the integrity, continuity and sense of ownership of our bodies. Here we explored whether the mere manipulation of the visual appearance of a virtual limb could influence the subjective feeling of ownership and the physiological responses (Skin Conductance Responses, SCRs) associated to a threatening stimulus approaching the virtual hand. Participants observed in first person perspective a virtual body having the right hand-forearm (i) connected by a normal wrist (Full-Limb) or a thin rigid wire connection (Wire) or (ii) disconnected because of a missing wrist (m-Wrist) or a missing wrist plus a plexiglass panel positioned between the hand and the forearm (Plexiglass). While the analysis of subjective ratings revealed that only the observation of natural full connected virtual limb elicited high levels of ownership, high amplitudes of SCRs were found also during observation of the non-natural, rigid wire connection condition. This result suggests that the conscious embodiment of an artificial limb requires a natural looking visual body appearance while implicit reactivity to threat may require physical body continuity, even non-naturally looking, that allows the implementation of protective reactions to threat.

Electroencephalographic correlates of sensorimotor integration and embodiment during the appreciation of virtual architectural environments

Nowadays there is the hope that neuroscientific findings will contribute to the improvement of building design in order to create environments which satisfy mans demands. This can be achieved through the understanding of neurophysiological correlates of architectural perception. To this aim, the electroencephalographic (EEG) signals of 12 healthy subjects were recorded during the perception of three immersive virtual reality environments (VEs). Afterwards, participants were asked to describe their experience in terms of Familiarity, Novelty, Comfort, Pleasantness, Arousal, and Presence using a rating scale from 1 to 9. These perceptual dimensions are hypothesized to influence the pattern of cerebral spectral activity, while Presence is used to assess the realism of the virtual stimulation. Hence, the collected scores were used to analyze the Power Spectral Density (PSD) of the EEG for each behavioral dimension in the theta, alpha and mu bands by means of time-frequency analysis and topographic statistical maps. Analysis of Presence resulted in the activation of the frontal-midline theta, indicating the involvement of sensorimotor integration mechanisms when subjects expressed to feel more present in the VEs. Similar patterns also characterized the experience of familiar and comfortable VEs. In addition, pleasant VEs increased the theta power across visuomotor circuits and activated the alpha band in areas devoted to visuospatial exploration and processing of categorical spatial relations. Finally, the de-synchronization of the mu rhythm described the perception of pleasant and comfortable VEs, showing the involvement of left motor areas and embodied mechanisms for environment appreciation. Overall, these results show the possibility to measure EEG correlates of architectural perception involving the cerebral circuits of sensorimotor integration, spatial navigation, and embodiment. These observations can help testing architectural hypotheses in order to design environments matching the changing needs of humans.

The Enactive Approach to Architectural Experience: A Neurophysiological Perspective on Embodiment, Motivation, and Affordances.

Over the last few years, the efforts to reveal through neuroscientific lens the relations between the mind, body, and built environment have set a promising direction of using neuroscience for architecture. However, little has been achieved thus far in developing a systematic account that could be employed for interpreting current results and providing a consistent framework for subsequent scientific experimentation. In this context, the enactive perspective is proposed as a guide to studying architectural experience for two key reasons. Firstly, the enactive approach is specifically selected for its capacity to account for the profound connectedness of the organism and the world in an active and dynamic relationship, which is primarily shaped by the features of the body. Thus, particular emphasis is placed on the issues of embodiment and motivational factors as underlying constituents of the body-architecture interactions. Moreover, enactive understanding of the relational coupling between body schema and affordances of architectural spaces singles out the two-way bodily communication between architecture and its inhabitants, which can be also explored in immersive virtual reality settings. Secondly, enactivism has a strong foothold in phenomenological thinking that corresponds to the existing phenomenological discourse in architectural theory and qualitative design approaches. In this way, the enactive approach acknowledges the available common ground between neuroscience and architecture and thus allows a more accurate definition of investigative goals. Accordingly, the outlined model of architectural subject in enactive terms—that is, a model of a human being as embodied, enactive, and situated agent, is proposed as a basis of neuroscientific and phenomenological interpretation of architectural experience.

Virtual reality in cognitive and motor rehabilitation: facts, fiction and fallacies

ABSTRACT Introduction: Over recent decades many researchers and clinicians have started to use Virtual Reality (VR) as a new technology for implementing innovative rehabilitation treatments in cognitive and motor domains. However, the expression ‘VR’ has often also been improperly used to refer to video games. Further, VR efficacy, often confused with that of video-game exercises, is still debated. Areas covered: In this review, we provide the scientific rationale for the advantages of using VR systems in rehabilitation and investigate whether the VR could really be a promising technique for the future of rehabilitation of patients, or if it is just an entertainment for scientists. In addition, we describe some of the most used devices in VR with their potential advantages for research and provide an overview of the recent evidence and meta-analyses in rehabilitation. Expert commentary: We highlight the efficacy and fallacies of VR in neurorehabilitation and discuss the important factors emerging from the use of VR, including the sense of presence and the embodiment over a virtual avatar, in developing future applications in cognitive and motor rehabilitation.

Come together: Human-avatar on-line interactions boost joint-action performance in apraxic patients

Abstract Limb apraxia (LA) is a high-order motor disorder linked to left-hemisphere damage. It is characterized by defective execution of purposeful actions upon delayed imitation, or verbal command when the actions are performed in isolated, non-naturalistic, conditions. Whether interpersonal interactions provide social affordances that activate neural resources different from those requested by individual action execution, which may improve LA performance, is unknown. To fill this gap, we measured interaction performance, behavioral and kinematic indexes of left-brain damaged patients with/without LA in a social reach-to-grasp task involving two different degrees of spatio-temporal interactivity with an avatar. We found that LA patients’ impairment in coordinating with the virtual partner was abolished in highly interactive conditions (where patients selected their actions on-line based on the behavior of the virtual partner) with respect to low interactive conditions (where actions were selected beforehand based on abstract instructions). Voxel-based-Lesion-Symptom-Mapping indicated that impairments in low-interactive conditions were underpinned by lesions of premotor, motor and insular areas, and of the basal ganglia. Our approach expands current understanding of the behavioral and neural correlates of interactive motor performance by highlighting the important role of social affordances, and provides novel, potentially important, views on rehabilitation of higher-order motor cognition disorders.

Visual appearance of a virtual upper limb modulates the temperature of the real hand: a thermal imaging study in Immersive Virtual Reality

To explore the link between Sense of Embodiment (SoE) over a virtual hand and physiological regulation of skin temperature, 24 healthy participants were immersed in virtual reality through a Head Mounted Display and had their real limb temperature recorded by means of a high‐sensitivity infrared camera. Participants observed a virtual right upper limb (appearing either normally, or with the hand detached from the forearm) or limb‐shaped non‐corporeal control objects (continuous or discontinuous wooden blocks) from a first‐person perspective. Subjective ratings of SoE were collected in each observation condition, as well as temperatures of the right and left hand, wrist and forearm. The observation of these complex, body and body‐related virtual scenes resulted in increased real hand temperature when compared to a baseline condition in which a 3d virtual ball was presented. Crucially, observation of non‐natural appearances of the virtual limb (discontinuous limb) and limb‐shaped non‐corporeal objects elicited high increase in real hand temperature and low SoE. In contrast, observation of the full virtual limb caused high SoE and low temperature changes in the real hand with respect to the other conditions. Interestingly, the temperature difference across the different conditions occurred according to a topographic rule that included both hands. Our study sheds new light on the role of an external hands visual appearance and suggests a tight link between higher‐order bodily self‐representations and topographic regulation of skin temperature.

Transitory Inhibition of the Left Anterior Intraparietal Sulcus Impairs Joint Actions: A Continuous Theta-Burst Stimulation Study

Although temporal coordination is a hallmark of motor interactions, joint action (JA) partners do not simply synchronize; rather, they dynamically adapt to each other to achieve a joint goal. We created a novel paradigm to tease apart the processes underlying synchronization and JA and tested the causal contribution of the left anterior intraparietal sulcus (aIPS) in these behaviors. Participants had to synchronize their congruent or incongruent movements with a virtual partner in two conditions: (i) being instructed on what specific action to perform, independently from what action the partner performed (synchronization), and (ii) being instructed to adapt online to the partners action (JA). Offline noninvasive inhibitory brain stimulation (continuous theta-burst stimulation) over the left aIPS selectively modulated interpersonal synchrony in JA by boosting synchrony during congruent interactions and impairing it during incongruent ones, while leaving performance in the synchronization condition unaffected. These results suggest that the left aIPS plays a causal role in supporting online adaptation to a partners action goal, whereas it is not necessarily engaged in social situations where the goal of the partner is irrelevant. This indicates that, during JAs, the integration of ones own and the partners action goal is supported by aIPS.

Frontal and occipito-temporal Theta activity as marker of error monitoring in Human-Avatar joint performance.

The discrepancy between expected outcome and real outcome is at the base of error coding, a crucial process during adaptive behaviours. Previous studies indicate that performing or observing errors elicits specific EEG markers (e.g. Theta). Here we show how unexpected changes in the movement trajectory of the virtual co-actor in a human-avatar dyadic paradigm are mapped into the error-monitoring system of the human partner. We asked individuals to synchronize their reach-to-grasp movements with those of a virtual partner in conditions that did (Interactive condition), or did not, require (Cued condition) spatio-temporal adaptation to the partner’s actions. Crucially, in certain trials the virtual partner suddenly changed its movement trajectory; thereby violating the human participant’s expectation. These trials showed that fronto-central error-related EEG markers increased as a function of the individual’s reliance on their partner’s behaviour. Source localization showed that observing violations of the expected movements also generated a Theta increase over occipito-temporal regions, highlighting visuo-motor processing during erroneous interactions. Significance Statement Our ability to coordinate with peers relies upon moment-to-moment prediction and integration of visual (i.e. observing the movements of others) and motor (completing our own actions) information. However, when the behaviour of our partners changes unexpectedly, our prediction appears to be incorrect. Here, we describe EEG error-related neuromarkers (ERN/Pe - Theta/Alpha modulations): when human participants perform a joint reach-to-grasp task with a virtual partner. We show that unexpected changes of the avatar trajectory are mapped into EEG error-markers according to the degree of interpersonal interdependence. Moreover, source analysis highlights that fronto-central and occipito-temporal regions generate Theta activity associated with processing visuo-motor information during social interactions.