Measures of agency

The functional role of conscious sensation of movement

This paper proposes a new framework for investigating neural signals sufficient for a conscious sensation of movement and their role in motor control. We focus on signals sufficient for proprioceptive awareness, particularly from muscle spindle activation and from primary motor cortex (M1). Our review of muscle vibration studies reveals that afferent signals alone can induce conscious sensations of movement. Similarly, studies employing peripheral nerve blocks suggest that efferent signals from M1 are sufficient for sensations of movement. On this basis, we show that competing theories of motor control assign different roles to sensation of movement. According to motor command theories, sensation of movement corresponds to an estimation of the current state based on afferent signals, efferent signals, and predictions. In contrast, within active inference architectures, sensations correspond to proprioceptive predictions driven by efferent signals from M1. The focus on sensation of movement provides a way to critically compare and evaluate the two theories. Our analysis offers new insights into the functional roles of movement sensations in motor control and consciousness.

Metacognition and sense of agency

Intelligent agents need to understand how they can change the world, and how they cannot change it, in order to make rational decisions for their forthcoming actions, and to adapt to their current environment. Previous research on the sense of agency, based largely on subjective ratings, failed to dissociate the sensitivity of sense of agency (i.e., the extent to which individual sense of agency tracks actual instrumental control over external events) from judgment criteria (i.e., the extent to which individuals self-attribute agency independent of their actual influence over external events). Furthermore, few studies have examined whether individuals have metacognitive access to the internal processes underlying the sense of agency. We developed a novel two-alternative-forced choice (2FAC) control detection task, in which participants identified which of two visual objects was more strongly controlled by their voluntary movement. The actual level of control over the target object was manipulated by adjusting the proportion of its motion that was driven by the participant's movement, compared to the proportion driven by a pre-recorded movement by another agent, using a staircase to hold 2AFC control detection accuracy at 70%. Participants identified which of the two visual objects they controlled, and also made a binary confidence judgment regarding their control detection judgment. We calculated a bias-free measure of first-order sensitivity (d') for detection control at any given level of participant's own movement. The proportion of pre-recorded movements determined by the stairecase could then be used as an index of control detection ability. We identified two distinct processes underlying first-order detection of control: one based on instantaneous sensory predictions for the current movement, and one based on detection of a regular motor-visual relation across a series of movements. Further, we found large individual differences across 40 particpants in metacognitive sensitivity (meta-d') even though first-order sensitivity of control detection was well controlled. Using structural equation modelling (SEM), we showed that metacognition was negatively correlated with the predictive process component of detection of control. This result is inconsistent with previous hypotheses that detection of control relies on metacognitive monitoring of a predictive circuit. Instead, it suggests that predictive mechanisms that compute sense of agency may operate unconsciously.

Induced feelings of external influence during instructed imaginations in healthy subjects

The psychopathological phenomenon of delusions of influence comprises variable disturbances of the self-environment-border leading to the feeling of external influence on thoughts, feelings, impulses or behaviors. Delusions of influence are a hallmark in psychotic illness, but nevertheless, attenuated forms can also appear in healthy individuals. Here we present a newly developed paradigm to induce and assess feelings of external influence during instructed imaginations in healthy individuals. In the current study, we asked 60 healthy individuals to visually imagine different objects. To induce feelings of external influence, we applied one of three different physical setups (low-amplitude transcranial direct current stimulation, eye contact, or skin-to-skin hand touch), and informed the participants whether or not an external influence was attempted during the respective trial. The physical setup (setup vs. no setup, Z = -3.847, p < 0.001, r = 0.497) as well as the information given to the participants (confirmation vs. negation, Z = -5.218, p < 0.001, r = 0.674) alone were able to modulate the feeling of external influence in all three interventions. The impact of information (whether influence was attempted or not attempted) significantly exceeded the impact of the physical setup on the ratings of experienced external influence (Z = -2.394, p = 0.016, r = 0.310). Moreover, the response latency correlated with the estimated feeling of external influence (r _S = 0.392, p = 0.002). Additional analyses addressed the influence of the emotional content of imagined objects and examined the intensity and emotional valence of the imaginations. Further supplemental analyses correlated external influence estimation of the participants with other psychopathological measures (trait markers for supernatural beliefs, proneness to hallucinations, and delusions and attributional style). In conclusion, this study endorses a quantitative model of psychopathological characteristics, in this case feelings of external influence that can be induced by external cues.

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.

Sense of agency for mental actions: Insights from a belief-based action-effect paradigm

A substantial body of research has converged on the idea that the sense of agency arises from the integration of multiple sources of information. In this study, we investigated whether a measurable sense of agency can be detected for mental actions, without the contribution of motor components. We used a fake action-effect paradigm, where participants were led to think that a motor action or a particular thought could trigger a sound. Results showed that the sense of agency, when measured through explicit reports, was of comparable strength for motor and mental actions. The intentional binding effect, a phenomenon typically associated with the experience of agency, was also observed for both motor and mental actions. Taken together, our results provide novel insights into the specific role of intentional cues in instantiating a sense of agency, even in the absence of motor signals.