Context-induced contrast and assimilation effects in explicit and implicit measures of agency

Social exclusion in a virtual Cyberball game reduces the virtual hand illusion

Sense of ownership and agency are two important aspects of the minimal self, but how self-perception is affected by social conditions remains unclear. Here, we studied how social inclusion or exclusion of participants in the course of a virtual Cyberball game would affect explicit judgments and implicit measures of ownership and agency (proprioceptive drift, skin conductance responses, and intentional binding, respectively) in a virtual hand illusion paradigm, in which a virtual hand moved in or out of sync with the participants' own hand. Results show that synchrony affected all four measures. More importantly, this effect interacted with social inclusion/exclusion in the Cyberball game for both ownership and agency measure, showing that social exclusion reduces perceived agency and ownership.

Neural correlates of an illusionary sense of agency caused by virtual reality

Sense of agency (SoA) is the sensation that self-actions lead to ensuing perceptual consequences. The prospective mechanism emphasizes that SoA arises from motor prediction and its comparison with actual action outcomes, while the reconstructive mechanism stresses that SoA emerges from retrospective causal processing about the action outcomes. Consistent with the prospective mechanism, motor planning regions were identified by neuroimaging studies using the temporal binding (TB) effect, a behavioral measure often linked to implicit SoA. Yet, TB also occurs during passive observation of another's action, lending support to the reconstructive mechanism, but its neural correlates remain unexplored. Here, we employed virtual reality (VR) to modulate such observation-based SoA and examined it with functional magnetic resonance imaging (fMRI). After manipulating an avatar hand in VR, participants passively observed an avatar's "action" and showed a significant increase in TB. The binding effect was associated with the right angular gyrus and inferior parietal lobule, which are critical nodes for inferential and agency processing. These results suggest that the experience of controlling an avatar may potentiate inferential processing within the right inferior parietal cortex and give rise to the illusionary SoA without voluntary action.

Vicarious ostracism reduces observers' sense of agency

Previous findings revealed that social ostracism reduces people's implicit sense of agency. Based on theoretical claims that observed behavior of others may be cognitively represented similarly to one's own behavior, we conducted two experiments to test whether people's own sense of agency can also be impaired by observed social exclusion of others. In Experiment 1, participants recalled episodes referring to vicarious ostracism or inclusion before completing a temporal interval estimation task to assess intentional binding effects (an established implicit measure of the sense of agency). In Experiment 2, participants immersed into a newly designed virtual Cyberball game, in which they witnessed a vicarious ostracism or inclusion scenario, before completing a Libet-style temporal estimation task and an agency questionnaire (an explicit measure of the sense of agency). The findings show, for the first time, that vicarious ostracism reduces both implicit and explicit measures of agency in observers.

Sense of agency as synecdoche: Multiple neurobiological mechanisms may underlie the phenomenon summarized as sense of agency

Functional magnetic resonance imaging (fMRI) studies on the sense of agency (SoA) have yielded heterogeneous findings identifying regional brain activity during tasks that probed SoA. In this review, we argue that the reason behind this between-study heterogeneity is a "synecdochic" way the field conceptualizes and studies SoA. Typically, a single feature is experimentally manipulated and then this is interpreted as covering all aspects of SoA. The purpose of this paper is to give an overview of the fMRI studies of SoA and attempt to provide meaningful categories whereby the heterogeneous findings may be classified. This classification is based on a separation of the experimental paradigms (Feedback Manipulations of ongoing movements, Action-Effect, and Sensory Attenuation) and type of report employed (implicit, explicit reports of graded or dichotic nature, and whether these concern self-other distinctions or sense of control). We only find that Feedback Manipulation and Action-Effect share common activation in supplementary motor area, insula and cerebellum in positive SoA and inferior frontal gyrus in the negative SoA, but observe large networks related to SoA only in Feedback Manipulation studies. To illustrate the advantages of this approach, we discuss the findings from an fMRI study which we conducted, within this framework.

Physical load reduces synchrony effects on agency and ownership in the virtual hand illusion

We used the virtual hand illusion paradigm to investigate the effect of physical load on perceived agency and body ownership. Participants pulled a resistance band that required exerting a force of 1 N, 10 N, or 20 N while operating a virtual hand that moved in synchronous or out of sync with their own hand. Explicit agency and ownership ratings were obtained, in addition to intentional binding and skin conductance as implicit measures of agency and ownership. Physical load increased perceived subjective load but showed no main effect, while synchrony effects were found on all agency and ownership measures. Interestingly, load did interact with synchrony in implicit agency and explicit ownership, by reducing and eliminating synchrony effects as movement synchrony was reduced with higher physical load. Furthermore, consistent with previous claims, implicit agency increased with perceived effort associated with higher physical load.

Cognitive load dissociates explicit and implicit measures of body ownership and agency

It is often claimed that the human self consists of perceived body ownership and agency, which are commonly assessed through explicit ownership and agency judgments and implicit measures, like proprioceptive drift, skin conductance responses, and intentional binding effects. Bottom-up multisensory integration and top-down modulation were predicted to be important for ownership and agency. In previous studies, cognitive load was revealed to affect the sense of agency in a top-down fashion, but its effect on ownership has not been fully investigated, not even its possibly different effect on explicit and implicit measures. Here we used cognitive load (small vs. large sets in a working-memory task) to disentangle explicit and implicit measures of ownership and agency in a task inducing the virtual hand illusion (VHI; stronger perceived ownership and agency over a virtual hand if it moves in synchrony with one's real hand). Results showed similar patterns for ownership and agency - both ownership and agency were affected by cognitive load, and importantly in the explicit measures, higher load increased the effect of synchrony (i.e., the VHI), but in implicit measures, higher load reduced indications of both ownership and agency. Hence, the load manipulation was selective with regard to the explicit versus implicit nature of the measure but not with respect to the measure's content. This provides strong evidence that explicit and implicit measures of both ownership and agency rely on at least partly separable informational sources, while the difference between ownership and agency as such does not seem to play a major role.

Explicit and implicit measures of body ownership and agency: affected by the same manipulations and yet independent

People are assumed to represent themselves in terms of body ownership and agency. Studies using the rubber- or virtual-hand illusion have assessed ownership and agency by means of explicit ownership and agency ratings and implicit measures, like proprioceptive drift in the case of ownership. These measures often show similar effects but also some discrepancies, suggesting that they rely on data sources that overlap, but not completely. To systematically assess commonalities and discrepancies, we adopted an immersed virtual hand illusion (VHI) design, in which three independent factors were manipulated: the synchrony between the movement of real and virtual effector, the type of effector, which was a virtual hand or triangle, and the spatial congruency between the real and virtual effector. Commonalities and discrepancies in the effects of these factors were assessed by crossing explicit and implicit measures for ownership and agency. While standard ratings were used as explicit measures, implicit ownership was assessed by means of proprioceptive drift and implicit agency by means of intentional binding. Results showed similar effect patterns for the two agency measures, which, however, were not correlated, different effect patterns for the two ownership measures, and a strong correlation between the two explicit measures. Taken altogether, our findings suggest that explicit and implicit measures of ownership and agency partly rely on shared informational sources, but seem to differ with respect to other sources that are integrated or with respect to the processed dimension (shape vs. time). The findings also suggest that some findings obtained with RHI designs might reflect more the unnatural situation that that design puts individuals into rather than generalizable mechanisms of computing perceived ownership and agency.