Moving Forward: On the Limits of Motor-Based Forward Models

Perceptual information processing in table tennis players: based on top-down hierarchical predictive coding

Long-term training induces neural plasticity in the visual cognitive processing cortex of table tennis athletes, who perform cognitive processing in a resource-conserving manner. However, further discussion is needed to determine whether the spatial processing advantage of table tennis players manifests in the early stage of sensory input or the late stage of processing. This study aims to explore the processing styles and neural activity characteristics of table tennis players during spatial cognitive processing. Spatial cognitive tasks were completed by 28 college students and 20 s-level table tennis players, and event-related potentials (ERP) data were recorded during the task. The behavioral results showed that the table tennis group performed better on the task than the college students group (control). The ERP results showed that the amplitude of the N1 component of the table tennis group was significantly lower than that of the control group. The amplitude of the P2 and P3 components of the table tennis group was higher than that of the control group. Table tennis players showed significant synergistic activity between electrodes in the β-band. The results of this study suggest that table tennis players significantly deploy attentional resources and cognitive control. Further, they employ stored motor experience to process spatial information in a hierarchical predictive coding manner.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-024-10171-4.

Fifty Percent of the Time, Tones Come Every Time: Stronger Prediction Error Effects on Neurophysiological Sensory Attenuation for Self-generated Tones

The N1/P2 amplitude reduction for self-generated tones in comparison to external tones in EEG, which has recently also been described for action observation, is an example of the so-called sensory attenuation. Whether this effect is dependent on motor-based or general predictive mechanisms is unclear. Using a paradigm, in which actions (button presses) elicited tones in only half the trials, this study examined how the processing of the tones is modulated by the prediction error in each trial in a self-performed action compared with action observation. In addition, we considered the effect of temporal predictability by adding a third condition, in which visual cues were followed by external tones in half the trials. The attenuation result patterns differed for N1 and P2 amplitudes, but neither showed an attenuation effect beyond temporal predictability. Interestingly, we found that both N1 and P2 amplitudes reflected prediction errors derived from a reinforcement learning model, in that larger errors coincided with larger amplitudes. This effect was stronger for tones following button presses compared with cued external tones, but only for self-performed and not for observed actions. Taken together, our results suggest that attenuation effects are partially driven by general predictive mechanisms irrespective of self-performed actions. However, the stronger prediction-error effects for self-generated tones suggest that distinct motor-related factors beyond temporal predictability, potentially linked to reinforcement learning, play a role in the underlying mechanisms. Further research is needed to validate these initial findings as the calculation of the prediction errors was limited by the design of the experiment.

Distinct role of central predictive mechanisms in tactile suppression

Tactile sensitivity on a limb is reduced during movement. This tactile suppression results presumably from central predictive mechanisms that downregulate sensations caused during voluntary action. Suppression also occurs during passive movements, indicating a role for peripheral mechanisms, questioning the predictive nature of suppression. Yet, predictions existing beyond the motor domain (non-motor predictions) can also modulate tactile suppression. This study aimed to disentangle central motor predictive and peripheral feedback mechanisms while accounting for non-motor predictions. Participants detected tactile stimuli on their limb shortly before it moved in an active or passive manner. Passive movements were either fully (100%) or partially (50%) predictable. We found tactile suppression during both active and passive movements irrespective of whether the passive movements were predictable. Importantly, tactile suppression was stronger in active than passive movements highlighting the specific role of central predictive mechanisms.

Violation of identity-specific action-effect prediction increases pupil size and attenuates auditory event-related potentials at P2 latencies when action-effects are behaviorally relevant

Self-initiated sensory action effects are widely assumed to lead to less intense perception and reduced neural responses compared to externally triggered stimuli (sensory attenuation). However, it is unclear if sensory attenuation occurs in all cases of action-effect prediction. Specifically, when predicted action-effects are relevant to determine follow-up actions attenuation could be detrimental. We quantified auditory event-related potentials (ERP) in electroencephalography (EEG) when human participants created two-sound sequences by pressing two keys on a keyboard associated with different pitch, giving rise to identity-specific action-effect prediction after the first keypress. The first sound corresponded to (congruent) or violated (incongruent) the predicted pitch and was either relevant for the selection of the second keypress to correctly complete the sequence (Relevance) or irrelevant (Control Movement), or there was only one keypress and sound (Baseline). We found a diminished P2-timed ERP component in incongruent compared to congruent trials when the sound was relevant for the subsequent action. This effect of action-effect prediction was due to an ERP reduction for incongruent relevant sounds compared to incongruent irrelevant sounds at P2 latencies and correlated negatively with modulations of pupil dilation. Contrary to our expectation, we did not observe an N1 modulation by congruency in any condition. Attenuation of the N1 component seems absent for predicted identity-specific auditory action effects, while P2-timed ERPs as well as pupil size are sensitive to predictability, at least when action effects are relevant for the selection of the next action. Incongruent relevant stimuli thereby take a special place and seem to be subject to attentional modulations and error processing.

Choice effects on temporal binding of action and outcomes: Examining the role of outcome focus and measures of time interval estimation

The ability to make one's own choices is vital to the experience of intentional behavior. Such agency experiences are reflected in the perceptual compression of time between actions and resulting outcomes. Whereas some studies show that choice limitations weaken temporal binding, other studies do not find such an effect. Reviewing the literature, we noted two potential factors that may moderate choice limitation effects on temporal binding: (a) the extent to which individuals represent their actions in terms of the consequences they produce; and (b) the response mode of the time interval estimation measurement where participants report numbers or use a slider to indicate time intervals. Testing these conceptual and methodological factors in two separate experiments yielded clear effects of choice limitation on temporal binding but no clear moderator role of the two factors. Interestingly, overall analyses showed that the choice limitation effect gradually vanishes over time.

Obedience induces agentic shifts by increasing the perceived time between own action and results

The concept of 'agentic shift,' introduced by Stanley Milgram, suggests that obedience reduces the sense of agency. In a recent study simulating the seminal work of Milgram, Caspar et al., 2016 examined this idea in a financial harm context. They demonstrated that, compared to situations of voluntary decision-making, coercion increases the perceived time between action and outcomes-suggested as a marker of diminished agency. Importantly, in this study, participants were agent and victim (relying on a reciprocal relationship) and first experienced free choices, followed by forced choices. This diverts from Milgram's original study, where participants were no victims but only agents who were forced to harm. The current study replicates and extends findings from the 2016 study by Caspar et al. in an online meeting setting, where participants served only as agents-similar to the original Milgram studies-while controlling the order of free and forced choice blocks. Substantiating earlier findings, forced choices reduced temporal binding (increased time interval estimations) compared to free choices independent of the order. We briefly discuss the importance of replications of coercion effects on the sense of agency, particularly in online decision-making settings.

Prediction of sensorimotor contingencies generates saccadic omission

With every movement of our eyes, the visual receptors in the retina are swiped across the visual scene. Saccades are the fastest and most frequent movements we perform, yet we remain unaware of the self-produced visual motion. Previous research has tried to identify a dedicated suppression mechanism that either actively or passively cancels vision at the time of saccades.1 Here, we investigated a novel theory, which states that saccadic omission results from habituation to the predicted sensory consequences of our own actions. We experimentally induced novel, i.e., artificial visual consequences of saccade performance by presenting gratings that were drifting faster than the flicker fusion frequency and that became visible only when participants performed saccades. We asked participants to perform more than 100 saccades in each session across these gratings to make the novel contingencies predictable for the sensorimotor system. We found that contrast sensitivity for intra-saccadic motion declined drastically after repeated exposure of such motion. The reduction in sensitivity was even specific to the saccade vector performed in habituation trials. Moreover, when subjects performed the same task in fixation, no reduction in sensitivity was observed. In a motion speed comparison task, we found that the reduction in contrast sensitivity is the consequence of silencing-predicted intra-saccadic visual motion. Our data demonstrate that the sensorimotor system selectively habituates to recurring intra-saccadic visual motion, suggesting an efficient prediction mechanism of visual stability.

Prime-induced illusion of control: The influence of unconscious priming on self-initiated actions and the role of regression to the mean

To what degree human cognition is influenced by subliminal stimuli is a controversial empirical question. One striking example was reported by Linser and Goschke (2007): participants overestimated how much control they had over objectively uncontrollable stimuli when masked congruent primes were presented immediately before the action. Critically, however, unawareness of the masked primes was established by post hoc data selection. In our preregistered study we sought to explore these findings while adjusting prime visibility based on individual thresholds, so that each participant underwent both visible and non-visible conditions. In experiment 1, N = 39 participants engaged in a control judgement task: following the presentation of a semantic prime, they freely selected between two keys, which triggered the appearance of a colored circle. The color of the circles, however, was independent of the key-press. Subsequently, participants assessed their perceived control over the circle's color, based on their key-presses, via a rating scale that ranged from 0 % (no control) to 100 % (complete control). Contrary to Linser and Goschke (2007)'s findings, this experiment demonstrated that predictive information influenced the experience of agency only when primes were consciously processed. In experiment 2, utilizing symbolic (arrow) primes, N = 35 participants had to rate their feeling of control over the effect-stimulus' identity during a two-choice identification paradigm (i.e., they were instructed to press a key corresponding to a target stimulus; with a contingency between target and effect stimulus of 75 %/25 %). The results revealed no significant influence of subliminal priming on agency perceptions. In summary, this study implies that unconscious stimuli may not exert a substantial influence on the conscious experience of agency, underscoring the need for careful consideration of methodological aspects and experimental design's impact on observed phenomena.

Eye did this! Sense of agency in eye movements

This study investigates the sense of agency (SoA) for saccades with implicit and explicit agency measures. In two eye tracking experiments, participants moved their eyes towards on-screen stimuli that subsequently changed color. Participants then either reproduced the temporal interval between saccade and color-change (Experiment 1) or reported the time points of these events with an auditory Libet clock (Experiment 2) to measure temporal binding effects as implicit indices of SoA. Participants were either made to believe to exert control over the color change or not (agency manipulation). Explicit ratings indicated that the manipulation of causal beliefs and hence agency was successful. However, temporal binding was only evident for caused effects, and only when a sufficiently sensitive procedure was used (auditory Libet clock). This suggests a feebler connection between temporal binding and SoA than previously proposed. The results also provide evidence for a relatively fast acquisition of sense of agency for previously never experienced types of action-effect associations. This indicates that the underlying processes of action control may be rooted in more intricate and adaptable cognitive models than previously thought. Oculomotor SoA as addressed in the present study presumably represents an important cognitive foundation of gaze-based social interaction (social sense of agency) or gaze-based human-machine interaction scenarios. PUBLIC SIGNIFICANCE STATEMENT: In this study, sense of agency for eye movements in the non-social domain is investigated in detail, using both explicit and implicit measures. Therefore, it offers novel and specific insights into comprehending sense of agency concerning effects induced by eye movements, as well as broader insights into agency pertaining to entirely newly acquired types of action-effect associations. Oculomotor sense of agency presumably represents an important cognitive foundation of gaze-based social interaction (social agency) or gaze-based human-machine interaction scenarios. Due to peculiarities of the oculomotor domain such as the varying degree of volitional control, eye movements could provide new information regarding more general theories of sense of agency in future research.

Self-initiation enhances perceptual processing of auditory stimuli in an online study

Understanding how the brain incorporates sensory and motor information will enable better theory building on human perception and behavior. In this study, we aimed to estimate the influence of predictive mechanisms on the magnitude and variability of sensory attenuation in two online samples. After the presentation of a visual cue stimulus, participants (Experiment 1: N = 224, Experiment 2: N = 84) compared the loudness of two consecutive tones in a two-alternative forced-choice task. In Experiment 1, the first tone was either self-initiated or not; in Experiment 2, the second tone was either self-initiated or not (active and passive condition, respectively). We further manipulated identity prediction (i.e., the congruence of pre-learned cue-sound combinations; congruent vs. incongruent), and the duration of the onset delay (to account for effects of attentional differences between the passive and active condition, 50 ms vs. 0 ms). We critically discuss our results within the framework of both classical (i.e., motor-based forward models) and contemporary approaches (i.e., predictive processing framework). Contrary to our preregistered hypothesis, we observed enhanced perceptual processing, instead of attenuation, for self-initiated auditory sensory input. Further, our results reveal an effect of fixed sound delays on the processing of motor and non-motor-based predictive information, and may point to according shifts in attention, leading to a perceptual bias. These results might best be captured by a hybrid explanatory model, combining predictions based on self-initiated motor action with a global predictive mechanism.

The right face at the wrong place: How motor intentions can override outcome monitoring

The concept of intentions is often taken for granted in the cognitive and neural sciences, and comparing outcomes with internal goals is seen as critical for our sense of agency. We created an experiment where participants decided which face they preferred, and we either created outcome errors by covertly switching the position of the chosen face or induced motor errors by deviating the mouse cursor, or we did both at the same time. In the final case, participants experienced a motor error, but the outcome ended up correct. The result showed that when they received the right face, but at the wrong place, participants rejected the outcome they actually wanted in a majority of the trials. Thus, contrary to common belief, higher-order outcomes do not always regulate our actions. Instead, motor "wrongness" might sometimes override goal "rightness" and lead us to reject the outcome we actually want.

Action does not enhance but attenuates predicted touch

Dominant motor control theories propose that the brain predicts and attenuates the somatosensory consequences of actions, referred to as somatosensory attenuation. Support comes from psychophysical and neuroimaging studies showing that touch applied on a passive hand elicits attenuated perceptual and neural responses if it is actively generated by one's other hand, compared to an identical touch from an external origin. However, recent experimental findings have challenged this view by providing psychophysical evidence that the perceived intensity of touch on the passive hand is enhanced if the active hand does not receive touch simultaneously with the passive hand (somatosensory enhancement) and by further attributing attenuation to the double tactile stimulation of the hands upon contact. Here, we directly contrasted the hypotheses of the attenuation and enhancement models regarding how action influences somatosensory perception by manipulating whether the active hand contacts the passive hand. We further assessed somatosensory perception in the absence of any predictive cues in a condition that turned out to be essential for interpreting the experimental findings. In three pre-registered experiments, we demonstrate that action does not enhance the predicted touch (Experiment 1), that the previously reported 'enhancement' effects are driven by the reference condition used (Experiment 2), and that self-generated touch is robustly attenuated regardless of whether the two hands make contact (Experiment 3). Our results provide conclusive evidence that action does not enhance but attenuates predicted touch and prompt a reappraisal of recent experimental findings upon which theoretical frameworks proposing a perceptual enhancement by action prediction are based.

Exploring the internal forward model: action-effect prediction and attention in sensorimotor processing

Action-effect predictions are believed to facilitate movement based on its association with sensory objectives and suppress the neurophysiological response to self- versus externally generated stimuli (i.e. sensory attenuation). However, research is needed to explore theorized differences in the use of action-effect prediction based on whether movement is uncued (i.e. volitional) or in response to external cues (i.e. stimulus-driven). While much of the sensory attenuation literature has examined effects involving the auditory N1, evidence is also conflicted regarding this component's sensitivity to action-effect prediction. In this study (n = 64), we explored the influence of action-effect contingency on event-related potentials associated with visually cued and uncued movement, as well as resultant stimuli. Our findings replicate recent evidence demonstrating reduced N1 amplitude for tones produced by stimulus-driven movement. Despite influencing motor preparation, action-effect contingency was not found to affect N1 amplitudes. Instead, we explore electrophysiological markers suggesting that attentional mechanisms may suppress the neurophysiological response to sound produced by stimulus-driven movement. Our findings demonstrate lateralized parieto-occipital activity that coincides with the auditory N1, corresponds to a reduction in its amplitude, and is topographically consistent with documented effects of attentional suppression. These results provide new insights into sensorimotor coordination and potential mechanisms underlying sensory attenuation.

Perception and action as viewed from the Theory of Event Coding: a multi-lab replication and effect size estimation of common experimental designs

The Theory of Event Coding (TEC) has influenced research on action and perception across the past two decades. It integrates several seminal empirical phenomena and it has continued to stimulate novel experimental approaches on the representational foundations of action control and perceptual experience. Yet, many of the most notable results surrounding TEC originate from an era of psychological research that relied on rather small sample sizes as judged by today's standards. This state hampers future research aiming to build on previous phenomena. We, therefore, provide a multi-lab re-assessment of the following six classical observations: response-effect compatibility, action-induced blindness, response-effect learning, stimulus-response binding, code occupation, and short-term response-effect binding. Our major goal is to provide precise estimates of corresponding effect sizes to facilitate future scientific endeavors. These effect sizes turned out to be considerably smaller than in the original reports, thus allowing for informed decisions on how to address each phenomenon in future work. Of note, the most relevant results of the original observations were consistently obtained in the present experiments as well.

Auditory N1 and P2 Attenuation in Action Observation: An Event-Related Potential Study Considering Effects of Temporal Predictability and Individualism

Tones that are generated by self-performed actions elicit attenuated N1 and P2 amplitudes, as measured by electroencephalography (EEG), compared to identical external tones, which is referred to as neurophysiological sensory attenuation (SA). At the same time, self-generated tones are perceived as less loud compared to external tones (perceptual SA). Action observation led in part to a similar neurophysiological and perceptual SA. The perceptual SA in observers was found in comparison to tones that were temporally predictable, and one study suggested that perceptual SA in observers might depend on the cultural dimension of individualism. In this study, we examined neurophysiological SA for tones elicited by self-performed and observed actions during simultaneous EEG acquisitions in two participants, extending the paradigm with a visual cue condition controlling for effects of temporal predictability. Moreover, we investigated the effect of individualism on neurophysiological SA in action observation. Relative to un-cued external tones, the N1 was only descriptively reduced for tones that were elicited by self-performed or observed actions and significantly attenuated for cued external tones. A P2 attenuation effect relative to un-cued external tones was found in all three conditions, with stronger effects for self- and other-generated tones than for cued external tones. We found no evidence for an effect of individualism. These findings add to previous evidence for neurophysiological SA in action performance and observation with a paradigm well-controlled for the effect of predictability and individualism, showing differential effects of the former on the N1 and P2 components, and no effect of the latter.

The auditory P2 differentiates self- from partner-produced sounds during joint action: Contributions of self-specific attenuation and temporal orienting of attention

Sensory attenuation of the auditory P2 event-related potential (ERP) has been shown to differentiate the sensory consequences of one's own from others' action in joint action contexts. However, recent evidence suggests that when people coordinate joint actions over time, temporal orienting of attention might simultaneously contribute to enhancing the auditory P2. The current study employed a joint tapping task in which partners produced tone sequences together to examine whether temporal orienting influences auditory ERP amplitudes during the time window of self-other differentiation. Our findings demonstrate that the combined requirements of coordinating with a partner toward a joint goal and immediately adjusting to the partner's tone timing enhance P2 amplitudes elicited by the partner's tone onsets. Furthermore, our findings replicate prior evidence for self-specific sensory attenuation of the auditory P2 in joint action, and additionally demonstrate that it occurs regardless of the coordination requirements between partners. Together, these findings provide evidence that temporal orienting and sensory attenuation both modulate the auditory P2 during joint action and suggest that both processes play a role in facilitating precise interpersonal coordination between partners.

The contribution of the basal ganglia and cerebellum to motor learning: A neuro-computational approach

Motor learning involves a widespread brain network including the basal ganglia, cerebellum, motor cortex, and brainstem. Despite its importance, little is known about how this network learns motor tasks and which role different parts of this network take. We designed a systems-level computational model of motor learning, including a cortex-basal ganglia motor loop and the cerebellum that both determine the response of central pattern generators in the brainstem. First, we demonstrate its ability to learn arm movements toward different motor goals. Second, we test the model in a motor adaptation task with cognitive control, where the model replicates human data. We conclude that the cortex-basal ganglia loop learns via a novelty-based motor prediction error to determine concrete actions given a desired outcome, and that the cerebellum minimizes the remaining aiming error.

My view on your actions: Dynamic changes in viewpoint-dependent auditory ERP attenuation during action observation

It has been suggested that during action observation, a sensory representation of the observed action is mapped onto one's own motor system. However, it is largely unexplored what this may imply for the early processing of the action's sensory consequences, whether the observational viewpoint exerts influence on this and how such a modulatory effect might change over time. We tested whether the event-related potential of auditory effects of actions observed from a first- versus third-person perspective show amplitude reductions compared with externally generated sounds, as revealed for self-generated sounds. Multilevel modeling on trial-level data showed distinct dynamic patterns for the two viewpoints on reductions of the N1, P2, and N2 components. For both viewpoints, an N1 reduction for sounds generated by observed actions versus externally generated sounds was observed. However, only during first-person observation, we found a temporal dynamic within experimental runs (i.e., the N1 reduction only emerged with increasing trial number), indicating time-variant, viewpoint-dependent processes involved in sensorimotor prediction during action observation. For the P2, only a viewpoint-independent reduction was found for sounds elicited by observed actions, which disappeared in the second half of the experiment. The opposite pattern was found in an exploratory analysis concerning the N2, revealing a reduction that increased in the second half of the experiment, and, moreover, a temporal dynamic within experimental runs for the first-person perspective, possibly reflecting an agency-related process. Overall, these results suggested that the processing of auditory outcomes of observed actions is dynamically modulated by the viewpoint over time.

Cancelling cancellation? Sensorimotor control, agency, and prediction

For decades, classic theories of action control and action awareness have been built around the idea that the brain predictively 'cancels' expected action outcomes from perception. However, recent research casts doubt over this basic premise. What do these new findings mean for classic accounts of action? Should we now 'cancel' old data, theories and approaches generated under this idea? In this paper, we argue 'No'. While doubts about predictive cancellation may urge us to fundamentally rethink how predictions shape perception, the wider pyramid using these ideas to explain action control and agentic experiences can remain largely intact. Some adaptive functions assigned to predictive cancellation can be achieved through quasi-predictive processes, that influence perception without actively tracking the probabilistic structure of the environment. Other functions may rely upon truly predictive processes, but not require that these predictions cancel perception. Appreciating the role of these processes may help us to move forward in explaining how agents optimise their interactions with the external world, even if predictive cancellation is cancelled from theory.

Tactile motor attention induces sensory attenuation for sounds

Sensory events appear reduced in intensity when we actively produce them. Here, we investigated sensory attenuation in a virtual reality setup that allowed us to manipulate the time of tactile feedback when pressing a virtual button. We asked whether tactile motor attention might shift to the tactile location that makes contact with the button. In experiment one, we found that a tactile impulse was perceived as more intense when button pressing. In a second experiment, participants pushed a button and estimated the intensity of sounds. We found sensory attenuation for sounds only when tactile feedback was provided at the time the movement goal was reached. These data indicate that attentional prioritization for the tactile modality during a goal-directed hand movement might lead to a transient reduction in sensitivity in other modalities, resulting in sensory attenuation for sounds.

Predictive Processing in Sign Languages: A Systematic Review

The objective of this article was to review existing research to assess the evidence for predictive processing (PP) in sign language, the conditions under which it occurs, and the effects of language mastery (sign language as a first language, sign language as a second language, bimodal bilingualism) on the neural bases of PP. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework. We searched peer-reviewed electronic databases (SCOPUS, Web of Science, PubMed, ScienceDirect, and EBSCO host) and gray literature (dissertations in ProQuest). We also searched the reference lists of records selected for the review and forward citations to identify all relevant publications. We searched for records based on five criteria (original work, peer-reviewed, published in English, research topic related to PP or neural entrainment, and human sign language processing). To reduce the risk of bias, the remaining two authors with expertise in sign language processing and a variety of research methods reviewed the results. Disagreements were resolved through extensive discussion. In the final review, 7 records were included, of which 5 were published articles and 2 were dissertations. The reviewed records provide evidence for PP in signing populations, although the underlying mechanism in the visual modality is not clear. The reviewed studies addressed the motor simulation proposals, neural basis of PP, as well as the development of PP. All studies used dynamic sign stimuli. Most of the studies focused on semantic prediction. The question of the mechanism for the interaction between one’s sign language competence (L1 vs. L2 vs. bimodal bilingual) and PP in the manual-visual modality remains unclear, primarily due to the scarcity of participants with varying degrees of language dominance. There is a paucity of evidence for PP in sign languages, especially for frequency-based, phonetic (articulatory), and syntactic prediction. However, studies published to date indicate that Deaf native/native-like L1 signers predict linguistic information during sign language processing, suggesting that PP is an amodal property of language processing.

Motivation(s) from control: response-effect contingency and confirmation of sensorimotor predictions reinforce different levels of selection

Humans and other animals live in dynamic environments. To reliably manipulate the environment and attain their goals they would benefit from a constant modification of motor-responding based on responses' current effect on the current environment. It is argued that this is exactly what is achieved by a mechanism that reinforces responses which have led to accurate sensorimotor predictions. We further show that evaluations of a response's effectiveness can occur simultaneously, driven by at least two different processes, each relying on different statistical properties of the feedback and affecting a different level of responding. Specifically, we show the continuous effect of (a) a sensorimotor process sensitive only to the conditional probability of effects given that the agent acted on the environment (i.e., action-effects) and of (b) a more abstract judgement or inference that is also sensitive to the conditional probabilities of occurrence of feedback given no action by the agent (i.e., inaction-effects). The latter process seems to guide action selection (e.g., should I act?) while the former the manner of the action's execution. This study is the first to show that different evaluation processes of a response's effectiveness influence different levels of responding.

The sense of agency in joint action: An integrative review

When people perform joint actions together, their individual actions (e.g., moving one end of a heavy couch) must be coordinated to achieve a collective goal (e.g., moving the couch across the room). Joint actions pose unique challenges for understanding people's sense of agency, because each person engaged in the joint action can have a sense of agency not only at the individual level (a sense that "I moved my end of the couch" or "My partner moved their end of the couch"), but also at the collective level (a sense that "We moved the couch together"). This review surveys research that has examined people's sense of agency in joint action, including explicit judgments of agency, implicit measures of agency, and first-hand accounts of agency in real-world settings. The review provides a comprehensive summary of the factors that influence individual- and collective-level agency in joint action; reveals the progress that has been made toward understanding different forms of collective-level agency in joint action, including the sense that agency is shared among co-actors and the sense that co-actors are acting as a single unit; and synthesizes evidence concerning the relationships between different measures of implicit agency and individual- versus collective-level agency in joint action. The review concludes by highlighting numerous outstanding questions and promising avenues for future research.

Actions of a Shaken Heart: Interoception Interacts with Action Processing

In the present study, we investigated the modulatory influence of the unconscious, bodily arousal on motor-related embodied information. Specifically, we examined how the interoceptive prediction error interacts with the event-related potentials linked to action-effect processing. Participants were asked to perform a task with self-initiated or externally-triggered sounds while receiving synchronous or false auditory cardiac feedback. The results found that interaction of interoceptive manipulation and action-effect processing modulates the frontal subcomponent of the P3 response. During the synchronous cardiac feedback, the P3 response to self-initiated tones was enhanced. During the false cardiac feedback, the frontal cortical response was reversed. N1 and P2 components were affected by the interoceptive manipulation, but not by the interaction of interoception and action processing. These findings provide experimental support for the theoretical accounts of the interaction between interoception and action processing within a framework of predictive coding, manifested particularly in the higher stages of action processing.

Judgments of agency are affected by sensory noise without recruiting metacognitive processing

Acting in the world is accompanied by a sense of agency, or experience of control over our actions and their outcomes. As humans, we can report on this experience through judgments of agency. These judgments often occur under noisy conditions. We examined the computations underlying judgments of agency, in particular under the influence of sensory noise. Building on previous literature, we studied whether judgments of agency incorporate uncertainty in the same way that confidence judgments do, which would imply that the former share computational mechanisms with metacognitive judgments. In two tasks, participants rated agency, or confidence in a decision about their agency, over a virtual hand that tracked their movements, either synchronously or with a delay and either under high or low noise. We compared the predictions of two computational models to participants' ratings and found that agency ratings, unlike confidence, were best explained by a model involving no estimates of sensory noise. We propose that agency judgments reflect first-order measures of the internal signal, without involving metacognitive computations, challenging the assumed link between the two cognitive processes.

Action Enhances Predicted Touch

It is widely believed that predicted tactile action outcomes are perceptually attenuated. The present experiments determined whether predictive mechanisms necessarily generate attenuation or, instead, can enhance perception-as typically observed in sensory cognition domains outside of action. We manipulated probabilistic expectations in a paradigm often used to demonstrate tactile attenuation. Adult participants produced actions and subsequently rated the intensity of forces on a static finger. Experiment 1 confirmed previous findings that action outcomes are perceived less intensely than passive stimulation but demonstrated more intense perception when active finger stimulation was removed. Experiments 2 and 3 manipulated prediction explicitly and found that expected touch during action is perceived more intensely than unexpected touch. Computational modeling suggested that expectations increase the gain afforded to expected tactile signals. These findings challenge a central tenet of prominent motor control theories and demonstrate that sensorimotor predictions do not exhibit a qualitatively distinct influence on tactile perception.

Environment-Related and Body-Related Components of the Minimal Self

Perceptual changes that an agent produces by efferent activity can become part of the agent’s minimal self. Yet, in human agents, efferent activities produce perceptual changes in various sensory modalities and in various temporal and spatial proximities. Some of these changes occur at the “biological” body, and they are to some extent conveyed by “private” sensory signals, whereas other changes occur in the environment of that biological body and are conveyed by “public” sensory signals. We discuss commonalties and differences of these signals for generating selfhood. We argue that despite considerable functional overlap of these sensory signals in generating self-experience, there are reasons to tell them apart in theorizing and empirical research about development of the self.

Sensory Attenuation in the Auditory Modality as a Window Into Predictive Processing

Self-generated auditory input is perceived less loudly than the same sounds generated externally. The existence of this phenomenon, called Sensory Attenuation (SA), has been studied for decades and is often explained by motor-based forward models. Recent developments in the research of SA, however, challenge these models. We review the current state of knowledge regarding theoretical implications about the significance of Sensory Attenuation and its role in human behavior and functioning. Focusing on behavioral and electrophysiological results in the auditory domain, we provide an overview of the characteristics and limitations of existing SA paradigms and highlight the problem of isolating SA from other predictive mechanisms. Finally, we explore different hypotheses attempting to explain heterogeneous empirical findings, and the impact of the Predictive Coding Framework in this research area.

Identification of a Brain Network Underlying the Execution of Freely Chosen Movements

Action selection refers to the decision regarding which action to perform in order to reach a desired goal, that is, the "what" component of intention. Whether the action is freely chosen or externally instructed involves different brain networks during the selection phase, but it is assumed that the way an action is selected should not influence the subsequent execution phase of the same movement. Here, we aim to test this hypothesis by investigating whether the modality of movement selection influences the brain networks involved during the execution phase of the movement. Twenty healthy volunteers performed a delayed response task in an event-related functional magnetic resonance imaging design to compare freely chosen and instructed unimanual or bimanual movements during the execution phase. Using activation analyses, we found that the pre-supplementary motor area (preSMA) and the parietal and cerebellar areas were more activated during the execution phase of freely chosen as compared to instructed movements. Connectivity analysis showed an increase of information flow between the right posterior parietal cortex and the cerebellum for freely chosen compared to instructed movements. We suggest that the parieto-cerebellar network is particularly engaged during freely chosen movement to monitor the congruence between the intentional content of our actions and their outcome.

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.

Intention-based and sensory-based predictions

We inhabit a continuously changing world, where the ability to anticipate future states of the environment is critical for adaptation. Anticipation can be achieved by learning about the causal or temporal relationship between sensory events, as well as by learning to act on the environment to produce an intended effect. Together, sensory-based and intention-based predictions provide the flexibility needed to successfully adapt. Yet it is currently unknown whether the two sources of information are processed independently to form separate predictions, or are combined into a common prediction. To investigate this, we ran an experiment in which the final tone of two possible four-tone sequences could be predicted from the preceding tones in the sequence and/or from the participants' intention to trigger that final tone. This tone could be congruent with both sensory-based and intention-based predictions, incongruent with both, or congruent with one while incongruent with the other. Trials where predictions were incongruent with each other yielded similar prediction error responses irrespectively of the violated prediction, indicating that both predictions were formulated and coexisted simultaneously. The violation of intention-based predictions yielded late additional error responses, suggesting that those violations underwent further differential processing which the violations of sensory-based predictions did not receive.

Zebrafish capable of generating future state prediction error show improved active avoidance behavior in virtual reality

Animals make decisions under the principle of reward value maximization and surprise minimization. It is still unclear how these principles are represented in the brain and are reflected in behavior. We addressed this question using a closed-loop virtual reality system to train adult zebrafish for active avoidance. Analysis of the neural activity of the dorsal pallium during training revealed neural ensembles assigning rules to the colors of the surrounding walls. Additionally, one third of fish generated another ensemble that becomes activated only when the real perceived scenery shows discrepancy from the predicted favorable scenery. The fish with the latter ensemble escape more efficiently than the fish with the former ensembles alone, even though both fish have successfully learned to escape, consistent with the hypothesis that the latter ensemble guides zebrafish to take action to minimize this prediction error. Our results suggest that zebrafish can use both principles of goal-directed behavior, but with different behavioral consequences depending on the repertoire of the adopted principles.

The auditory brain in action: Intention determines predictive processing in the auditory system-A review of current paradigms and findings

According to the ideomotor theory, action may serve to produce desired sensory outcomes. Perception has been widely described in terms of sensory predictions arising due to top-down input from higher order cortical areas. Here, we demonstrate that the action intention results in reliable top-down predictions that modulate the auditory brain responses. We bring together several lines of research, including sensory attenuation, active oddball, and action-related omission studies: Together, the results suggest that the intention-based predictions modulate several steps in the sound processing hierarchy, from preattentive to evaluation-related processes, also when controlling for additional prediction sources (i.e., sound regularity). We propose an integrative theoretical framework—the extended auditory event representation system (AERS), a model compatible with the ideomotor theory, theory of event coding, and predictive coding. Initially introduced to describe regularity-based auditory predictions, we argue that the extended AERS explains the effects of action intention on auditory processing while additionally allowing studying the differences and commonalities between intention- and regularity-based predictions—we thus believe that this framework could guide future research on action and perception.

Sensory Attenuation of the Auditory P2 Differentiates Self- from Partner-Produced Sounds during Joint Action

Successful human interaction relies on people's ability to differentiate between the sensory consequences of their own and others' actions. Research in solo action contexts has identified sensory attenuation, that is, the selective perceptual or neural dampening of the sensory consequences of self-produced actions, as a potential marker of the distinction between self- and externally produced sensory consequences. However, very little research has examined whether sensory attenuation distinguishes self- from partner-produced sensory consequences in joint action contexts. The current study examined whether sensory attenuation of the auditory N1 or P2 ERPs distinguishes self- from partner-produced tones when pairs of people coordinate their actions to produce tone sequences that match a metronome pace. We did not find evidence of auditory N1 attenuation for either self- or partner-produced tones. Instead, the auditory P2 was attenuated for self-produced tones compared to partner-produced tones within the joint action. These findings indicate that self-specific attenuation of the auditory P2 differentiates the sensory consequences of one's own from others' actions during joint action. These findings also corroborate recent evidence that N1 attenuation may be driven by general rather than action-specific processes and support a recently proposed functional dissociation between auditory N1 and P2 attenuation.

The anterior midcingulate cortex might be a neuronal substrate for the ideomotor mechanism

The way the brain controls voluntary movements for normal and pathological subject remains puzzling. In this selective review, we provide unreported harmonies between the anterior midcingulate cortex (aMCC) activities and the ideomotor mechanism postulating that voluntary movements are controlled by the anticipation of the expected perceptual consequences of an action, critically involving bidirectional interplay of a given motor activity and corresponding sensory feedback. Among other evidence, we found that the required asymmetry in the bidirectional interplay between a given motor command and its expected sensory effect could rely on the specific activity of aMCC neurons when observing errors and successes. We confirm this hypothesis by presenting a pathological perspective, studying obsessive-compulsive and other related disorders in which hyperactivated and uniform aMCC activities should lead to a circular-reflex process that results in persistent ideas and repeated actions. By evaluating normal and pathological data, we propose considering the aMCC at a central position within the cerebral network involved in the ideomotor mechanism.

Computational models of the "active self" and its disturbances in schizophrenia

The notion that self-disorders are at the root of the emergence of schizophrenia rather than a symptom of the disease, is getting more traction in the cognitive sciences. This is in line with philosophical approaches that consider an enactive self, constituted through action and interaction with the environment. We thereby analyze different definitions of the self and evaluate various computational theories lending to these ideas. Bayesian and predictive processing are promising approaches for computational modeling of the "active self". We evaluate their implementation and challenges in computational psychiatry and cognitive developmental robotics. We describe how and why embodied robotic systems provide a valuable tool in psychiatry to assess, validate, and simulate mechanisms of self-disorders. Specifically, mechanisms involving sensorimotor learning, prediction, and self-other distinction, can be assessed with artificial agents. This link can provide essential insights to the formation of the self and new avenues in the treatment of psychiatric disorders.

The spatial specificity of sensory attenuation for self-touch

Self-touch is sensed less intense as touch produced by another person. According to the standard explanation, if predicted and actual sensations match, the intensity of the touch will be reduced. Here, we asked whether sensory attenuation is spatially specific. To this end, participants laid their left hand under a metal arc on which a force sensor was mounted. Pressing the sensor caused one of two motors to rotate a lever that either touched the index or the ring finger. We took care that no cues would reveal in advance which of the motors would move in order to leave participants uninformed about the finger that will be stimulated. Any reduction in felt intensity of the touch could therefore be induced only by the efference copy of the touching movement. We found strong spatial specificity of sensory attenuation of self-touch, selecting between two fingers of the same hand.

The Forward Model: A Unifying Theory for the Role of the Cerebellum in Motor Control and Sense of Agency

For more than two decades, there has been converging evidence for an essential role of the cerebellum in non-motor functions. The cerebellum is not only important in learning and sensorimotor processes, some growing evidences show its implication in conditional learning and reward, which allows building our expectations about behavioral outcomes. More recent work has demonstrated that the cerebellum is also required for the sense of agency, a cognitive process that allows recognizing an action as our own, suggesting that the cerebellum might serve as an interface between sensorimotor function and cognition. A unifying model that would explain the role of the cerebellum across these processes has not been fully established. Nonetheless, an important heritage was given by the field of motor control: the forward model theory. This theory stipulates that movements are controlled based on the constant interactions between our organism and its environment through feedforward and feedback loops. Feedforward loops predict what is going to happen, while feedback loops confront the prediction with what happened so that we can react accordingly. From an anatomical point of view, the cerebellum is at an ideal location at the interface between the motor and sensory systems, as it is connected to cerebral, striatal, and spinal entities via parallel loops, so that it can link sensory and motor systems with cognitive processes. Recent findings showing that the cerebellum participates in building the sense of agency as a predictive and comparator system will be reviewed together with past work on motor control within the context of the forward model theory.

Predictive Processing in Cognitive Robotics: A Review

Predictive processing has become an influential framework in cognitive sciences. This framework turns the traditional view of perception upside down, claiming that the main flow of information processing is realized in a top-down, hierarchical manner. Furthermore, it aims at unifying perception, cognition, and action as a single inferential process. However, in the related literature, the predictive processing framework and its associated schemes, such as predictive coding, active inference, perceptual inference, and free-energy principle, tend to be used interchangeably. In the field of cognitive robotics, there is no clear-cut distinction on which schemes have been implemented and under which assumptions. In this letter, working definitions are set with the main aim of analyzing the state of the art in cognitive robotics research working under the predictive processing framework as well as some related nonrobotic models. The analysis suggests that, first, research in both cognitive robotics implementations and nonrobotic models needs to be extended to the study of how multiple exteroceptive modalities can be integrated into prediction error minimization schemes. Second, a relevant distinction found here is that cognitive robotics implementations tend to emphasize the learning of a generative model, while in nonrobotics models, it is almost absent. Third, despite the relevance for active inference, few cognitive robotics implementations examine the issues around control and whether it should result from the substitution of inverse models with proprioceptive predictions. Finally, limited attention has been placed on precision weighting and the tracking of prediction error dynamics. These mechanisms should help to explore more complex behaviors and tasks in cognitive robotics research under the predictive processing framework.

Studying the sense of agency in the absence of motor movement: an investigation into temporal binding of tactile sensations and auditory effects

People form coherent representations of goal-directed actions. Such agency experiences of intentional action are reflected by a shift in temporal perception: self-generated motor movements and subsequent sensory effects are perceived to occur closer together in time—a phenomenon termed intentional binding. Building on recent research suggesting that temporal binding occurs without intentionally performing actions, we further examined whether such perceptual compression occurs when motor action is fully absent. In three experiments, we used a novel sensory-based adaptation of the Libet clock paradigm to assess how a brief tactile sensation on the index finger and a resulting auditory stimulus perceptually bind together in time. Findings revealed robust temporal repulsion (instead of binding) between tactile sensation and auditory effect. Temporal repulsion was attenuated when participants could anticipate the identity and temporal onset (two crucial components of intentional action) of the tactile sensation. These findings are briefly discussed in the context of differences between intentional movement and anticipated bodily sensations in shaping action coherence and agentic experiences.

Evaluating the evidence for expectation suppression in the visual system

Reports of expectation suppression have shaped the development of influential predictive coding-based theories of visual perception. However recent work has highlighted confounding factors that may mimic or inflate expectation suppression effects. In this review, we describe four confounds that are prevalent across experiments that tested for expectation suppression: effects of surprise, attention, stimulus repetition and adaptation, and stimulus novelty. With these confounds in mind we then critically review the evidence for expectation suppression across probabilistic cueing, statistical learning, oddball, action-outcome learning and apparent motion designs. We found evidence for expectation suppression within a specific subset of statistical learning designs that involved weeks of sequence learning prior to neural activity measurement. Across other experimental contexts, whereby stimulus appearance probabilities were learned within one or two testing sessions, there was inconsistent evidence for genuine expectation suppression. We discuss how an absence of expectation suppression could inform models of predictive processing, repetition suppression and perceptual decision-making. We also provide suggestions for designing experiments that may better test for expectation suppression in future work.

Temporal Binding in Multisensory and Motor-Sensory Contexts: Toward a Unified Model

Our senses receive a manifold of sensory signals at any given moment in our daily lives. For a coherent and unified representation of information and precise motor control, our brain needs to temporally bind the signals emanating from a common causal event and segregate others. Traditionally, different mechanisms were proposed for the temporal binding phenomenon in multisensory and motor-sensory contexts. This paper reviews the literature on the temporal binding phenomenon in both multisensory and motor-sensory contexts and suggests future research directions for advancing the field. Moreover, by critically evaluating the recent literature, this paper suggests that common computational principles are responsible for the temporal binding in multisensory and motor-sensory contexts. These computational principles are grounded in the Bayesian framework of uncertainty reduction rooted in the Helmholtzian idea of unconscious causal inference.

The encoding of stochastic regularities is facilitated by action-effect predictions

Our brains continuously build and update predictive models of the world, sources of prediction being drawn for example from sensory regularities and/or our own actions. Yet, recent results in the auditory system indicate that stochastic regularities may not be easily encoded when a rare medium pitch deviant is presented between frequent high and low pitch standard sounds in random order, as reflected in the lack of sensory prediction error event-related potentials [i.e., mismatch negativity (MMN)]. We wanted to test the implication of the predictive coding theory that predictions based on higher-order generative models-here, based on action intention, are fed top-down in the hierarchy to sensory levels. Participants produced random sequences of high and low pitch sounds by button presses in two conditions: In a "specific" condition, one button produced high and the other low pitch sounds; in an "unspecific" condition, both buttons randomly produced high or low-pitch sounds. Rare medium pitch deviants elicited larger MMN and N2 responses in the "specific" compared to the "unspecific" condition, despite equal sound probabilities. These results thus demonstrate that action-effect predictions can boost stochastic regularity-based predictions and engage higher-order deviance detection processes, extending previous notions on the role of action predictions at sensory levels.

Intentional action and limitation of personal autonomy. Do restrictions of action selection decrease the sense of agency?

The experience of being an intentional agent is a key component of personal autonomy. Here, we tested how undermining intentional action affects the sense of agency as indexed by intentional binding. In three experiments using the Libet clock paradigm, participants judged the onset of their action (key presses) and resulting effect (auditory stimuli) under conditions of no, partial, or full autonomy over selecting and timing their actions. In all cases, we observed a moderate to strong intentional binding effect. However, we found no evidence for an influence of personal autonomy on intentional binding. These findings thus suggest that being unable to decide how and when to perform actions does not affect the perceived temporal binding between action and effect, a phenomenon suggested to be associated with the implicit sense of agency. We discuss the implications of our findings in the context of research on personal autonomy and goal-directed behavior.

Commonalities and differences in predictive neural processing of discrete vs continuous action feedback

Sensory action consequences are highly predictable and thus engage less neural resources compared to externally generated sensory events. While this has frequently been observed to lead to attenuated perceptual sensitivity and suppression of activity in sensory cortices, some studies conversely reported enhanced perceptual sensitivity for action consequences. These divergent findings might be explained by the type of action feedback, i.e., discrete outcomes vs. continuous feedback. Therefore, in the present study we investigated the impact of discrete and continuous action feedback on perceptual and neural processing during action feedback monitoring. During fMRI data acquisition, participants detected temporal delays (0-417 ms) between actively or passively generated wrist movements and visual feedback that was either continuously provided during the movement or that appeared as a discrete outcome. Both feedback types resulted in (1) a neural suppression effect (active<passive) in a largely shared network including bilateral visual and somatosensory cortices, cerebellum and temporoparietal areas. Yet, compared to discrete outcomes, (2) processing continuous feedback led to stronger suppression in right superior temporal gyrus (STG), Heschl´s gyrus, and insula suggesting specific suppression of features linked to continuous feedback. Furthermore, (3) BOLD suppression in visual cortex for discrete outcomes was specifically related to perceptual enhancement. Together, these findings indicate that neural representations of discrete and continuous action feedback are similarly suppressed but might depend on different predictive mechanisms, where reduced activation in visual cortex reflects facilitation specifically for discrete outcomes, and predictive processing in STG, Heschl´s gyrus, and insula is particularly relevant for continuous feedback.

Similarities and Differences between Performers and Observers in Processing Auditory Action Consequences: Evidence from Simultaneous EEG Acquisition

In our social environment, we easily distinguish stimuli caused by our own actions (e.g., water splashing when I fill my glass) from stimuli that have an external source (e.g., water splashing in a fountain). Accumulating evidence suggests that processing the auditory consequences of self-performed actions elicits N1 and P2 ERPs of reduced amplitude compared to physically identical but externally generated sounds, with such reductions being ascribed to neural predictive mechanisms. It is unexplored, however, whether the sensory processing of action outcomes is similarly modulated by action observation (e.g., water splashing when I observe you filling my glass). We tested 40 healthy participants by applying a methodological approach for the simultaneous EEG recording of two persons: An observer observed button presses executed by a performer in real time. For the performers, we replicated previous findings of a reduced N1 amplitude for self- versus externally generated sounds. This pattern differed significantly from the one in observers, whose N1 for sounds generated by observed button presses was not attenuated. In turn, the P2 amplitude was reduced for processing action- versus externally generated sounds for both performers and observers. These findings show that both action performance and observation affect the processing of action-generated sounds. There are, however, important differences between the two in the timing of the effects, probably related to differences in the predictability of the actions and thus also the associated stimuli. We discuss how these differences might contribute to recognizing the stimulus as caused by self versus others.

Temporal binding and agency under startle

Forward models are a component of the motor system that predicts the sensory consequences of our actions. These models play several key roles in motor control and are hypothesized to underlie (among other things) the two phenomena under investigation in this experiment: The feeling of agency that we have over self-initiated actions (as opposed to reflexes), and "temporal binding", in which self-caused sensations are judged to have occurred earlier in time than they actually did. This experiment probes the connection between forward models and both of these phenomena using the "Startle" paradigm. In the Startle paradigm, a startlingly loud sound causes people to initiate a prepared action at a very short latency. It is hypothesized that the latency of a startle-initiated action is so short that normal cortical operations (including forward models) are circumvented. This experiment replicates the temporal-binding effect and simultaneously measures participants' sense of agency over their actions. The results show that both the temporal-binding effect and the sense of agency we have over our own actions is disrupted under the startle paradigm in line with the theory that these phenomena both rely on forward models. Furthermore, this experiment provides evidence in support of the claim that a startle-induced action is qualitatively different from other actions.

Transcranial direct current stimulation improves action-outcome monitoring in schizophrenia spectrum disorder

Patients with schizophrenia spectrum disorder often demonstrate impairments in action-outcome monitoring. Passivity phenomena and hallucinations, in particular, have been related to impairments of efference copy-based predictions which are relevant for the monitoring of outcomes produced by voluntary action. Frontal transcranial direct current stimulation has been shown to improve action-outcome monitoring in healthy subjects. However, whether transcranial direct current stimulation can improve action monitoring in patients with schizophrenia spectrum disorder remains unknown. We investigated whether transcranial direct current stimulation can improve the detection of temporal action-outcome discrepancies in patients with schizophrenia spectrum disorder. On 4 separate days, we applied sham or left cathodal/right anodal transcranial direct current stimulation in a randomized order to frontal (F3/F4), parietal (CP3/CP4) and frontoparietal (F3/CP4) areas of 19 patients with schizophrenia spectrum disorder and 26 healthy control subjects. Action-outcome monitoring was assessed subsequent to 10 min of sham/transcranial direct current stimulation (1.5 mA). After a self-generated (active) or externally generated (passive) key press, subjects were presented with a visual outcome (a dot on the screen), which was presented after various delays (0-417 ms). Participants had to detect delays between the key press and the visual consequence. Symptom subgroups were explored based on the presence or absence of symptoms related to a paranoid-hallucinatory syndrome. In general, delay-detection performance was impaired in the schizophrenia spectrum disorder compared to the healthy control group. Interaction analyses showed group-specific (schizophrenia spectrum disorder versus healthy control group) and symptom-specific (with/without relevant paranoid-hallucinatory symptoms) transcranial direct current stimulation effects. Post hoc tests revealed that frontal transcranial direct current stimulation improved the detection of long delays in active conditions and reduced the proportion of false alarms in undelayed trials of the passive condition in patients. The patients with no or few paranoid-hallucinatory symptoms benefited especially from frontal transcranial direct current stimulation in active conditions, while improvement in the patients with paranoid-hallucinatory symptoms was predominantly reflected in reduced false alarm rates in passive conditions. These data provide some first evidence for the potential utility of transcranial direct current stimulation in improving efference copy mechanisms and action-outcome monitoring in schizophrenia spectrum disorder. Current data indicate that improving efference copy-related processes can be especially effective in patients with no or few positive symptoms, while intersensory matching (i.e. task-relevant in passive conditions) could be more susceptible to improvement in patients with paranoid-hallucinatory symptoms.

Sense of Agency in Multi-Step Actions

In our daily lives, we frequently execute actions that require several steps to bring about the outcome. However, investigations on how the sense of agency—the sense of controlling our actions and their outcomes—evolves in multi-step actions are still lacking. The purpose of the present research is to fill this gap. In the present study, the participants executed one-step, two-step, and three-step actions in which one, two, or three keys had to be pressed consecutively to generate a tone. We used sensory attenuation as an implicit measure of the sense of agency. Sensory attenuation means that self-produced sensory effects are perceived as less intense than externally generated effects. In the present experiment, sensory attenuation was measured in a psychophysical paradigm and increased in multi-step actions compared to the one-step action. We also asked the participants to explicitly rate the amount to which they felt that they had generated the tone. Ratings were highest in the one-step condition and dropped for multi-step actions, thus showing the opposite pattern of the sensory attenuation data. We assume that enhanced sensory attenuation in multi-step actions could be due to increased effort or more accurate sensorimotor predictions of action effects. The decrease in explicit ratings for multi-step actions might be attributed to reduced perception of causality.

Shadowing in the manual modality

Motor simulation has emerged as a mechanism for both predictive action perception and language comprehension. By deriving a motor command, individuals can predictively represent the outcome of an unfolding action as a forward model. Evidence of simulation can be seen via improved participant performance for stimuli that conform to the participant's individual characteristics (an egocentric bias). There is little evidence, however, from individuals for whom action and language take place in the same modality: sign language users. The present study asked signers and nonsigners to shadow (perform actions in tandem with various models), and the delay between the model and participant ("lag time") served as an indicator of the strength of the predictive model (shorter lag time = more robust model). This design allowed us to examine the role of (a) motor simulation during action prediction, (b) linguistic status in predictive representations (i.e., pseudosigns vs. grooming gestures), and (c) language experience in generating predictions (i.e., signers vs. nonsigners). An egocentric bias was only observed under limited circumstances: when nonsigners began shadowing grooming gestures. The data do not support strong motor simulation proposals, and instead highlight the role of (a) production fluency and (b) manual rhythm for signer productions. Signers showed significantly faster lag times for the highly skilled pseudosign model and increased temporal regularity (i.e., lower standard deviations) compared to nonsigners. We conclude sign language experience may (a) reduce reliance on motor simulation during action observation, (b) attune users to prosodic cues (c) and induce temporal regularities during action production.