Illusion of sense of self-agency: discrepancy between the predicted and actual sensory consequences of actions modulates the sense of self-agency, but not the sense of self-ownership

It is proposed that knowledge of motor commands is used to distinguish self-generated sensation from externally generated sensation. In this paper, we show that the sense of self-agency, that is the sense that I am the one who is generating an action, largely depends on the degree of discrepancy resulting from comparison between the predicted and actual sensory feedback. In Experiment 1, the sense of self-agency was reduced when the presentation of the tone was unpredictable in terms of timing and its frequency, although in fact the tone was self-produced. In Experiment 2, the opposite case was found to occur. That is, participants experienced illusionary sense of self-agency when the externally generated sensations happened to match the prediction made by forward model. In Experiment 3, the sense of self-agency was reduced when there was a discrepancy between the predicted and actual sensory consequences, regardless of presence or absence of a discrepancy between the intended and actual consequences of actions. In all the experiments, a discrepancy between the predicted and actual feedback had no effects on sense of self-ownership, that is the sense that I am the one who is undergoing an experience. These results may suggest that both senses of self are mutually independent.     

Vicarious action preparation does not result in sensory attenuation of auditory action effects

The perception of sensory effects generated by one’s own actions is typically attenuated compared to the same effects generated externally. However, it is unclear whether this specifically relates to self-generation. Recent studies showed that sensory attenuation mainly relies on action preparation, not actual action execution. Hence, an attenuation of sensory effects generated by another person might occur if these actions can be anticipated and thus be prepared for.Here, we compared the perceived loudness of sounds generated by one’s own actions and actions of another person that either could or could not be anticipated. We found an attenuation of the perceived loudness for self- as compared to other-generated sounds. This difference was independent of whether the sound-eliciting actions of the other person could be anticipated or not. Thus, sensory attenuation seems to be specifically tied to self-generation instead of being a secondary effect of agent-independent preparation for an upcoming action.     

Active inference, sensory attenuation and illusions

Active inference provides a simple and neurobiologically plausible account of how action and perception are coupled in producing (Bayes) optimal behaviour. This can be seen most easily as minimising prediction error: we can either change our predictions to explain sensory input through perception. Alternatively, we can actively change sensory input to fulfil our predictions. In active inference, this action is mediated by classical reflex arcs that minimise proprioceptive prediction error created by descending proprioceptive predictions. However, this creates a conflict between action and perception; in that, self-generated movements require predictions to override the sensory evidence that one is not actually moving. However, ignoring sensory evidence means that externally generated sensations will not be perceived. Conversely, attending to (proprioceptive and somatosensory) sensations enables the detection of externally generated events but precludes generation of actions. This conflict can be resolved by attenuating the precision of sensory evidence during movement or, equivalently, attending away from the consequences of self-made acts. We propose that this Bayes optimal withdrawal of precise sensory evidence during movement is the cause of psychophysical sensory attenuation. Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly. Finally, if attenuation is removed, the force-matching illusion disappears and false (delusional) inferences about agency emerge. This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects—and the reduction in the magnitude of the illusion in schizophrenia. Active inference therefore links the neuromodulatory optimisation of precision to sensory attenuation and illusory phenomena during the attribution of agency in normal subjects. It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement—like schizophrenia and Parkinsonism—syndromes that implicate abnormal modulatory neurotransmission.     

Predictable and self-initiated visual motion is judged to be slower than computer generated motion

Self-initiated action effects are often perceived as less intense than identical but externally generated stimuli. It is thought that forward models within the sensorimotor system pre-activate cortical representations of predicted action effects, reducing perceptual sensitivity and attenuating neural responses. As self-agency and predictability are seldom manipulated simultaneously in behavioral experiments, it is unclear if self-other differences depend on predictable action effect contingencies, or if both self- and externally generated stimuli are modulated similarly by predictability. We factorially combined variation in (1) predictability of action effects, (2) spatial congruence, and (3) performance by the self or computer to dissociate these influences on a visual discrimination task. Participants performed 2AFC speed judgments. Self-initiated motion was judged to be slower than computer-initiated motion when action effect contingencies were predictable, while spatial congruence influenced speed judgments only when action effect contingencies were unpredictable. Results are discussed in relation to current theories of sensory attenuation.     

The self in action effects: selective attenuation of self-generated sounds

The immediate experience of self-agency, that is, the experience of generating and controlling our actions, is thought to be a key aspect of selfhood. It has been suggested that this experience is intimately linked to internal motor signals associated with the ongoing actions. These signals should lead to an attenuation of the sensory consequences of one’s own actions and thereby allow classifying them as self-generated. The discovery of shared representations of actions between self and other, however, challenges this idea and suggests similar attenuation of one’s own and other’s sensory action effects.Here, we tested these assumptions by comparing sensory attenuation of self-generated and observed sensory effects. More specifically, we compared the loudness perception of sounds that were either self-generated, generated by another person or a computer. In two experiments, we found a reduced perception of loudness intensity specifically related to self-generation. Furthermore, the perception of sounds generated by another person and a computer did not differ from each other. These findings indicate that one’s own agentive influence upon the outside world has a special perceptual quality which distinguishes it from any sort of external influence, including human and non-human sources. This suggests that a real sense of self-agency is not a socially shared but rather a unique and private experience.     

A specific role for efferent information in self-recognition

We investigated the specific contribution of efferent information in a self-recognition task. Subjects experienced a passive extension of the right index finger, either as an effect of moving their left hand via a lever ('self-generated action'), or imposed externally by the experimenter ('externally-generated action'). The visual feedback was manipulated so that subjects saw either their own right hand ('view own hand' condition) or someone else's right hand ('view other's hand' condition) during the passive extension of the index finger. Both hands were covered with identical gloves, so that discrimination on the basis of morphological differences was not possible. Participants judged whether the right hand they saw was theirs or not. Self-recognition was significantly more accurate when subjects were themselves the authors of the action, even though visual and proprioceptive information always specified the same posture, and despite the fact that subjects judged the effect and not the action per se. When the passive displacement of the participants right index finger was externally generated, and only afferent information was available, self-recognition performance dropped to near-chance levels. Differences in performance across conditions reflect the distinctive contribution of efferent information to self-recognition, and argue against a dominant role of proprioception in self-recognition.     

The ability to self-tickle following Rapid Eye Movement sleep dreaming

Self-produced tactile stimulation usually feels less tickly--is perceptually attenuated--relative to the same stimulation produced externally. This is not true, however, for individuals with schizophrenia. Here, we investigate whether the lack of attenuation to self-produced stimuli seen in schizophrenia also occurs for normal participants following REM dreams. Fourteen participants were stimulated on their left palm with a tactile stimulation device which allowed the same stimulus to be generated by the participant or by the experimenter. The level of self-tickling attenuation did not differ between REM and non-REM sleep awakening conditions, where presence or absence of an accompanying dream was not controlled for. However, for the female participants, when awakening occurred from an REM sleep dream, self-stimulation ratings were higher than for external stimulation, whereas ratings after NREM sleep unaccompanied by a dream were lower for self-stimulation than for external stimulation. These results indicate deficits in self-monitoring and a confusion between self- and externally generated stimulation accompany REM dream formation.     

Deluding the motor system

How do we know that our own actions belong to us? How are we able to distinguish self-generated sensory events from those that arise externally? In this paper, I will briefly discuss experiments that were designed to investigate these questions. In particular, I will review psychophysical and neuroimaging studies that have investigated how we recognise the consequences of our own actions, and why patients with delusions of control confuse self-produced and externally produced actions and sensations. Studies investigating the failure of this 'self-monitoring' mechanism in patients with delusions of control will be discussed in the context of the hypothesis that overactivity in the parietal cortex and the cerebellum contribute to the misattribution of an action to an external source.     

Both motor prediction and conceptual congruency between preview and action-effect contribute to explicit judgment of agency

The sense of agency is the sense that one is causing an action. The inferential account of the sense of agency proposes that we experience the sense of agency when we infer that one’s own thoughts are the cause of an action. According to this account, the inference occurs when a thought appears in consciousness prior to an action, is consistent with the action, and is not accompanied by conspicuous other causes of the action. Alternatively, a predictive account of the sense of agency proposes that sensory prediction based on efferent (motor) information plays a critical role in generating the sense of agency. The present study investigated whether the sense of agency depended primarily on the conceptual congruence between preview information (i.e., to elicit a thought) and actual sensory feedback as suggested by the inferential account, or whether it depended primarily on the sensory-motor congruence between prediction and actual sensory feedback as suggested by the predictive account. The results indicated that both of these factors did contribute to the sense of agency, although sensory-motor congruence appears to have a more robust impact.     

Performed or observed keyboard actions affect pianists' judgements of relative pitch

Action can affect visual perception if the action's expected sensory effects resemble a concurrent unstable or deviant event. To determine whether action can also change auditory perception, participants were required to play pairs of octave-ambiguous tones by pressing successive keys on a piano or computer keyboard and to judge whether each pitch interval was rising or falling. Both pianists and nonpianist musicians gave significantly more “rising” responses when the order of key presses was left-to-right than when it was right-to-left, in accord with the pitch mapping of the piano. However, the effect was much larger in pianists. Pianists showed a similarly large effect when they passively observed the experimenter pressing keys on a piano keyboard, as long as the keyboard faced the participant. The results suggest that acquired action–effect associations can affect auditory perceptual judgement.     

The joint role of trained,untrained, and observed actions at the origins of goal recognition

Recent findings across a variety of domains reveal the benefits of self-produced experience on object exploration, object knowledge, attention, and action perception. The influence of active experience may be particularly important in infancy, when motor development is undergoing great changes. Despite the importance of self-produced experience, we know that infants and young children are eventually able to gain knowledge through purely observational experience. In the current work, three-month-old infants were given experience with object-directed actions in one of three forms and their recognition of the goal of grasping actions was then assessed in a habituation paradigm. All infants were given the chance to manually interact with the toys without assistance (a difficult task for most three-month-olds). Two of the three groups were then given additional experience with object-directed actions, either through active training (in which Velcro mittens helped infants act more efficiently) or observational training. Findings support the conclusion that self-produced experience is uniquely informative for action perception and suggest that individual differences in spontaneous motor activity may interact with observational experience to inform action perception early in life.     

Perceiving by proxy: Effect-based action control with unperceivable effects

Anticipations of future sensory events have the potential of priming motor actions that would typically cause these events. Such effect anticipations are generally assumed to rely on previous physical experiences of the contingency of own actions and their ensuing effects. Here we propose that merely imagined action effects may influence behaviour similarly as physically experienced action effects do. Three experiments in the response–effect compatibility paradigm show that the mere knowledge of action–effect contingencies is indeed sufficient to incorporate these effects into action control even if the effects are never experienced as causally linked to own actions. The experiments further highlight constraints for this mechanism which seems to be rather effortful and to depend on explicit intentions.     

Sensation of agency and perception of temporal order

After adaptation to a fixed temporal delay between actions and their sensory consequences, stimuli delivered during the delay are perceived to occur prior to actions. Temporal judgments are also influenced by the sensation of agency (experience of causing our own actions and their sensory consequences). Sensory consequences of voluntary actions are perceived to occur earlier in time than those of involuntary actions. However, it is unclear whether temporal order illusions influence the sensation of agency. Thus, we tested how the illusionary reversal of motor actions and sound events affect the sensation of agency. We observed an absence of the sensation of agency in the auditory modality in a condition in which sounds were falsely perceived as preceding motor acts relative to the perceived temporal order in the control condition. This finding suggests a strong association between the sensation of agency and the temporal order perception of actions and their consequences.     

Can you tickle yourself if you swap bodies with someone else?

The effect of the body transfer illusion on the perceived strength of self- and externally-generated “tickle” sensations was investigated. As expected, externally generated movement produced significantly higher ratings of tickliness than those associated with self-generated movements. Surprisingly, the body transfer illusion had no influence on the ratings of tickliness, suggesting that highly surprising, and therefore hard to predict, experiences of body image and first-person perspective do not abolish the attenuation of tickle sensations. In addition, evidence was found that a version of the rubber hand illusion exists within the body transfer illusion. We situate our findings within the larger debate over sensory attenuation: (1) there is an attenuation of prediction errors that depends upon the context in which sensory input is predicted (i.e., efference copy), and (2) sensory attenuation is a necessary consequence of self-generated movement irrespective of context (i.e., active inference). The results support the notion of active inference.     

The Experience of Agency: Feelings, Judgments, and Responsibility

ABSTRACT— The experience of agency refers to the experience of being in control both of one's own actions and, through them, of events in the external world. Recent experimental studies have investigated how people recognise a particular event as being caused by their own action or by that of another person. These studies suggest that people match sensory inputs to a prediction based on the action they are performing. Other studies have contrasted voluntary actions to physically similar but passive body movements. These studies suggest that voluntary action triggers wide-ranging changes in the spatial and temporal experience not only of one's own body but also of external events. Prediction and monitoring of the consequences of one's own motor commands produces characteristic experiences that form our normal, everyday feeling of being in control of our life. We conclude by discussing the implications of recent psychological work for our notions of responsibility for action.     

The self in action: lessons from delusions of control

Patients with delusions of control are abnormally aware of the sensory consequences of their actions and have difficulty with on-line corrections of movement. As a result they do not feel in control of their movements. At the same time they are strongly aware of the action being intentional. This leads them to believe that their actions are being controlled by an external agent. In contrast, the normal mark of the self in action is that we have very little experience of it. Most of the time we are not aware of the sensory consequences of our actions or of the various subtle corrections that we make during the course of goal-directed actions. We know that we are agents and that we are successfully causing the world to change. But as actors we move through the world like shadows glimpsed only occasional from the corner of an eye.     

Baby do–baby see!: How action production influences action perception in infants

With a series of four experiments we show that self-produced actions influence infants’ perception of actions performed by others. After having played with an object, 7–11-month-olds simultaneously watched two videos presenting adults who act on either the same object or a different one. The 9- and 11-month-old preferred to watch the same-object video indicating an influence of action production on action perception at this age. Follow-up studies showed that this influence was restricted to object-related actions. Agentive experience enhanced interest in actions with objects, but not in watching objects or persons per se. These findings indicate that infants are not only interested in acting on objects themselves, but that this experience increases their interest in the actions of other people with the same object.     

Goal saliency boosts infants’ action prediction for human manual actions,but not for mechanical claws

Previous research indicates that infants’ prediction of the goals of observed actions is influenced by own experience with the type of agent performing the action (i.e., human hand vs. non-human agent) as well as by action-relevant features of goal objects (e.g., object size). The present study investigated the combined effects of these factors on 12-month-olds’ action prediction. Infants’ (N = 49) goal-directed gaze shifts were recorded as they observed 14 trials in which either a human hand or a mechanical claw reached for a small goal area (low-saliency goal) or a large goal area (high-saliency goal). Only infants who had observed the human hand reaching for a high-saliency goal fixated the goal object ahead of time, and they rapidly learned to predict the action goal across trials. By contrast, infants in all other conditions did not track the observed action in a predictive manner, and their gaze shifts to the action goal did not change systematically across trials. Thus, high-saliency goals seem to boost infants’ predictive gaze shifts during the observation of human manual actions, but not of actions performed by a mechanical device. This supports the assumption that infants’ action predictions are based on interactive effects of action-relevant object features (e.g., size) and own action experience.     

The role of mechanical impact in action-related auditory attenuation

A number of studies have shown that sounds temporally close to one’s own finger movements elicit lower-amplitude auditory event-related potentials (ERPs) than do the same tones when they are only listened to. In these studies, the actions have involved making a mechanical contact with an object. In the present study, the role of mechanical contact with an object was investigated in action-related auditory attenuation. In three experiments, participants performed a time-interval production task. In each experiment, in one condition the action involved touching an object, but no mechanical contact was made in the other. The estimated tone-related ERP contributions to the action–tone coincidence ERP waveforms (calculated by subtracting the action-related ERP from the coincidence ERP) were more attenuated when the action involved moving the finger and making a mechanical contact at the end of the movement. However, when participants kept their finger on a piezoelectric element and applied pressure impulses without moving their finger, the action did not result in stronger attenuation of the tone-related auditory ERP estimates. Although these results may suggest that auditory ERP attenuation is stronger for actions resulting in mechanical impact, they also imply that mechanical impact may confound and lead to the overestimation of auditory ERP attenuation in such paradigms, because the impact may result in faint but audible sounds.     

Conscious awareness of action potentiates sensorimotor learning

Many everyday skills are unconsciously learned through repetitions of the same behaviour by binding independent motor acts into unified sets of actions. However, our ability to be consciously aware of producing newly and highly trained motor skills raises the question of the role played by conscious awareness of action upon skill acquisition. In this study we strengthened conscious awareness of self-produced sequential finger movements by way of asking participants to judge their performance in terms of maximal fluency after each trial. Control conditions in which participants did not make any judgment or performance-unrelated judgments were also included. Findings indicate that conscious awareness of action, enhanced via subjective appraisal of motor efficiency, potentiates sensorimotor learning and skilful motor production in optimising the processing and sequencing of action units, as compared to the control groups. The current work lends support to the claim that the learning and skilful expression of sensorimotor behaviours might be grounded upon our ability to be consciously aware of our own motor capability and efficiency.