Sensory attenuation in the absence of movement: Differentiating motor action from sense of agency

Somatosensory influence on auditory cortical response of self-generated sound

Motor execution which results in the generation of sounds attenuates the cortical response to these self-generated sounds. This attenuation has been explained as a result of motor relevant processing. The current study shows that corresponding somatosensory inputs can also change the auditory processing of a self-generated sound. We recorded auditory event-related potentials (ERP) in response to self-generated sounds and assessed how the amount of auditory attenuation changed according to the somatosensory inputs. The sound stimuli were generated by a finger movement that pressed on a virtual object, which was produced by a haptic robotic device. Somatosensory inputs were modulated by changing the stiffness of this virtual object (low and high) in an unpredictable manner. For comparison purposes, we carried out the same test with a computer keyboard, which is conventionally used to induce the auditory attenuation of self-generated sound. While N1 and P2 attenuations were clearly induced in the control condition with the keyboard as has been observed in previous studies, when using the robotic device the amplitude of N1 was found to vary according to the stiffness of the virtual object. The amplitude of N1 in the low stiffness condition was similar to that found using the keyboard for the same condition but not in the high stiffness condition. In addition, P2 attenuation did not differ between stiffness conditions. The waveforms of auditory ERP after 200 ms also differed according to the stiffness conditions. The estimated source of N1 attenuation was located in the right parietal area. These results suggest that somatosensory inputs during movement can modify the auditory processing of self-generated sound. The auditory processing of self-generated sound may represent self-referenced processing like an embodied process or an action-perception mechanism.

Modelling sensory attenuation as Bayesian causal inference across two datasets

INTRODUCTION

To interact with the environment, it is crucial to distinguish between sensory information that is externally generated and inputs that are self-generated. The sensory consequences of one's own movements tend to induce attenuated behavioral- and neural responses compared to externally generated inputs. We propose a computational model of sensory attenuation (SA) based on Bayesian Causal Inference, where SA occurs when an internal cause for sensory information is inferred.

METHODS

Experiment 1investigates sensory attenuation during a stroking movement. Tactile stimuli on the stroking finger were suppressed, especially when they were predictable. Experiment 2 showed impaired delay detection between an arm movement and a video of the movement when participants were moving vs. when their arm was moved passively. We reconsider these results from the perspective of Bayesian Causal Inference (BCI). Using a hierarchical Markov Model (HMM) and variational message passing, we first qualitatively capture patterns of task behavior and sensory attenuation in simulations. Next, we identify participant-specific model parameters for both experiments using optimization.

RESULTS

A sequential BCI model is well equipped to capture empirical patterns of SA across both datasets. Using participant-specific optimized model parameters, we find a good agreement between data and model predictions, with the model capturing both tactile detections in Experiment 1 and delay detections in Experiment 2.

DISCUSSION

BCI is an appropriate framework to model sensory attenuation in humans. Computational models of sensory attenuation may help to bridge the gap across different sensory modalities and experimental paradigms and may contribute towards an improved description and understanding of deficits in specific patient groups (e.g. schizophrenia).

ERP correlates of agency processing in joint action

In the Ouija board phenomenon, the lack of agency experienced by the players leads them to attribute the movement of the planchette to spirits. The aim of this study was to investigate the neural and cognitive mechanisms involved in generating the sense of agency in such a joint action context. Two players (a participant and a confederate) jointly moved a Ouija board-style planchette containing a wireless mouse. This, in turn, moved a digital board on the screen. Participants reported a greater sense of agency in the condition where they had complete control of the planchette (the 'self' condition), and least agency when they passively held the planchette while it was moved by the confederate ('other' condition), with the two 'joint' action conditions in between. While the N1 peak did not differ between conditions, the early part of the N1 differentiated between the joint action conditions, and the solo action conditions. In contrast, the Tb and P2 components differed between the 'other' condition and the 'self' and 'joint' conditions. These findings are discussed with reference to motor-prediction and attentional mechanisms.

Rejecting unfairness enhances the implicit sense of agency in the human brain

Sense of agency (SoA) describes the feeling of control over one's actions and their consequences. One proposed index of implicit SoA is temporal compression, which refers to the phenomenon that voluntary actions and their outcomes are perceived as closer in time than they actually are. The present study measured temporal compression in the social norm violation situation. In two experiments participants joined in an Ultimatum game (UG), in which they were presented with offers that varied in fairness and they could choose to accept or reject the offers by pressing buttons. A neutral sound would occur after their choices in the UG and the participants had to estimate the time interval between their button pressing and the occurrence of the sound, and EEG signals were recorded during the task. Experiment 1 demonstrated that rejecting unfair offers decreased the perceived interval between action and outcome compared to accepting fair offers, suggesting a higher level of SoA after rejecting unfair offers. Experiment 2 replicated these results and further revealed an attenuated N1 in response to the sound following rejections of unfairness. Taken together, these results highlight the importance of social norms in affecting people's behaviors and agency experiences.

My choice, my actions: self-determination, not instrumental value of outcomes enhances outcome monitoring during learning

Freedom of choice enhances our sense of agency. During goal-directed behavior, the freedom to choose between different response options increases the neural processing of positive and negative feedback, indicating enhanced outcome monitoring under conditions of high agency experience. However, it is unclear whether this enhancement is predominantly driven by an increased salience of self- compared to externally determined action outcomes or whether differences in the perceived instrumental value of outcomes contribute to outcome monitoring in goal-directed tasks. To test this, we recorded electroencephalography while participants performed a reinforcement learning task involving free choices, action-relevant forced choices, and action-irrelevant forced choices. We observed larger midfrontal theta power and N100 amplitudes for feedback following free choices compared with action-relevant and action-irrelevant forced choices. In addition, a Reward Positivity was only present for free but not forced choice outcomes. Crucially, our results indicate that enhanced outcome processing is not driven by the relevance of outcomes for future actions but rather stems from the association of outcomes with recent self-determined choice. Our findings highlight the pivotal role of self-determination in tracking the consequences of our actions and contribute to an understanding of the cognitive processes underlying the choice-induced facilitation in outcome monitoring.

Neurophysiological evidence of motor preparation in inner speech and the effect of content predictability

Self-generated overt actions are preceded by a slow negativity as measured by electroencephalogram, which has been associated with motor preparation. Recent studies have shown that this neural activity is modulated by the predictability of action outcomes. It is unclear whether inner speech is also preceded by a motor-related negativity and influenced by the same factor. In three experiments, we compared the contingent negative variation elicited in a cue paradigm in an active vs. passive condition. In Experiment 1, participants produced an inner phoneme, at which an audible phoneme whose identity was unpredictable was concurrently presented. We found that while passive listening elicited a late contingent negative variation, inner speech production generated a more negative late contingent negative variation. In Experiment 2, the same pattern of results was found when participants were instead asked to overtly vocalize the phoneme. In Experiment 3, the identity of the audible phoneme was made predictable by establishing probabilistic expectations. We observed a smaller late contingent negative variation in the inner speech condition when the identity of the audible phoneme was predictable, but not in the passive condition. These findings suggest that inner speech is associated with motor preparatory activity that may also represent the predicted action-effects of covert actions.

Neural signatures of memory gain through active exploration in an oculomotor-auditory learning task

Active engagement improves learning and memory, and self- versus externally generated stimuli are processed differently: perceptual intensity and neural responses are attenuated. Whether the attenuation is linked to memory formation remains unclear. This study investigates whether active oculomotor control over auditory stimuli-controlling for movement and stimulus predictability-benefits associative learning, and studies the underlying neural mechanisms. Using EEG and eye tracking we explored the impact of control during learning on the processing and memory recall of arbitrary oculomotor-auditory associations. Participants (N = 23) learned associations through active exploration or passive observation, using a gaze-controlled interface to generate sounds. Our results show faster learning progress in the active condition. ERPs time-locked to the onset of sound stimuli showed that learning progress was linked to an attenuation of the P3a component. The detection of matching movement-sound pairs triggered a target-matching P3b. There was no general modulation of ERPs through active learning. However, we found continuous variation in the strength of the memory benefit across participants: some benefited more strongly from active control during learning than others. This was paralleled in the strength of the N1 attenuation effect for self-generated stimuli, which was correlated with memory gain in active learning. Our results show that control helps learning and memory and modulates sensory responses. Individual differences during sensory processing predict the strength of the memory benefit. Taken together, these results help to disentangle the effects of agency, unspecific motor-based neuromodulation, and predictability on ERP components and establish a link between self-generation effects and active learning memory gain.

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.

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.

Sensory suppression and increased neuromodulation during actions disrupt memory encoding of unpredictable self-initiated stimuli

Actions modulate sensory processing by attenuating responses to self- compared to externally generated inputs, which is traditionally attributed to stimulus-specific motor predictions. Yet, suppression has been also found for stimuli merely coinciding with actions, pointing to unspecific processes that may be driven by neuromodulatory systems. Meanwhile, the differential processing for self-generated stimuli raises the possibility of producing effects also on memory for these stimuli; however, evidence remains mixed as to the direction of the effects. Here, we assessed the effects of actions on sensory processing and memory encoding of concomitant, but unpredictable sounds, using a combination of self-generation and memory recognition task concurrently with EEG and pupil recordings. At encoding, subjects performed button presses that half of the time generated a sound (motor-auditory; MA) and listened to passively presented sounds (auditory-only; A). At retrieval, two sounds were presented and participants had to respond which one was present before. We measured memory bias and memory performance by having sequences where either both or only one of the test sounds were presented at encoding, respectively. Results showed worse memory performance - but no differences in memory bias -, attenuated responses, and larger pupil diameter for MA compared to A sounds. Critically, the larger the sensory attenuation and pupil diameter, the worse the memory performance for MA sounds. Nevertheless, sensory attenuation did not correlate with pupil dilation. Collectively, our findings suggest that sensory attenuation and neuromodulatory processes coexist during actions, and both relate to disrupted memory for concurrent, albeit unpredictable sounds.

The Role of Action-Effect Contingency on Sensory Attenuation in the Absence of Movement

Stimuli that have been generated by a person's own willed motor actions generally elicit a suppressed electrophysiological, as well as phenomenological, response than identical stimuli that have been externally generated. This well-studied phenomenon, known as sensory attenuation, has mostly been studied by comparing ERPs evoked by self-initiated and externally generated sounds. However, most studies have assumed a uniform action-effect contingency, in which a motor action leads to a resulting sensation 100% of the time. In this study, we investigated the effect of manipulating the probability of action-effect contingencies on the sensory attenuation effect. In Experiment 1, participants watched a moving, marked tickertape while EEG was recorded. In the full-contingency (FC) condition, participants chose whether to press a button by a certain mark on the tickertape. If a button press had not occurred by the mark, a sound would be played a second later 100% of the time. If the button was pressed before the mark, the sound was not played. In the no-contingency (NC) condition, participants observed the same tickertape; in contrast, however, if participants did not press the button by the mark, a sound would occur only 50% of the time (NC-inaction). Furthermore, in the NC condition, if a participant pressed the button before the mark, a sound would also play 50% of the time (NC-action). In Experiment 2, the design was identical, except that a willed action (as opposed to a willed inaction) triggered the sound in the FC condition. The results were consistent across the two experiments: Although there were no differences in N1 amplitude between conditions, the amplitude of the Tb and P2 components were smaller in the FC condition compared with the NC-inaction condition, and the amplitude of the P2 component was also smaller in the FC condition compared with the NC-action condition. The results suggest that the effect of contingency on electrophysiological indices of sensory attenuation may be indexed primarily by the Tb and P2 components, rather than the N1 component which is most commonly studied.