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Here, the predictions we considered involved some sort of action intended to generate a sound. This approach receives more and more attention in many labs not only in the field of perception but also in social neuroscience and in animal research. In one approach, in collaboration with Marc Schönwiesner and Julian Keil (Montreal), we manipulated the pre-reflective sense of agency using single pulse transcranial magnetic stimulation over primary motor cortex (Timm et al., 2014, JN). In this way we could generate an involuntary motor act (a finger movement), that, in turn, generated a sound by pressing a button. Interestingly, this involuntary motor act was nevertheless the result of activity in the participant’s motor cortex, and we can thus speculate that the efference copy of the command would be issued as well. Thus, all other things being equal to a voluntary button press, with this procedure the participant would not feel as the agent of the self-initiated sound. Results show no N1-attenuation for self-initiated sounds under these circumstances, thus we can speculate that sensory attenuation of auditory brain responses to self-initiated sounds depends on a pre-reflective sense of agency. In another important series of studies (with Iria SanMiguel as driving force), we combined the basic ingredients of paradigms tapping into regularity extraction in the auditory domain and paradigms tapping into motor-driven prediction effects in auditory processing (SanMiguel et al., 2013). Participants repeatedly initiated a sound by pressing a button, and on a low percentage of the button presses, the sound was unexpectedly omitted. With this procedure we induced a very strong and simple auditory prediction that was precisely time-locked to the motor act. Thus, by omitting the expected sound, we could gain access to the underlying neural activity coding for the prediction. The findings obtained were quite remarkable: when the self-initiated sound was omitted an auditory-like response (as revealed by event-related potentials and functional imaging measures) was elicited. In cooperation with Sonja Kotz (Maastricht) we could show that patients suffering from lesions in the cerebellum show particular deficits in predictive processing (Knolle et al., 2013, Cortex); in cooperation with Juanita Todd (Newcastle, Australia), we investigated predictive processing in Schizophrenia (in prep.).

Predictive models that aid perception need to take into account possible sensory consequences of our (even potential) actions. Therefore, own actions are an important source of sensory prediction. Predictions arising from self-performed motor acts modulate the processing of incoming stimulation. In particular, it is assumed that with every action command formulated in motor cortices, a copy of this command (the efference copy) is sent to sensory cortices. In this way, the expected sensory consequences of the motor command (the corollary discharge) can be estimated via forward modeling. Thus, when the self-caused sensory stimulation arrives, it will interact with the preexisting or simultaneous prediction. The effects of the corollary discharge have been often measured as a suppression of sensory responses elicited by self-initiated stimulation. The impact of this simple but fundamental mechanism ramifies into a myriad possible functions along all levels of cognitive complexity, ranging from basic sensory functions such as enabling stable perception despite bodily movements, up to complex high-level cognitive functions such as granting the individual with the sense of agency.

Research on action-driven effects on sensory processing has proceeded rather independently from research on predictive models in sensory processing. However, we like to propose that action-driven predictions are but another form of sensory prediction, and that when it comes to their impact on sensory processing, all sensory predictions can be regarded in the same way, irrespective of their origin. We believe the auditory system makes use of all available sources of information to put incoming stimulation in context and make sense of it. Therefore, there must be a shared representational code for all auditory predictions. Moreover, common mechanisms must operate in different domains. For example, a substantial effort has been put into investigating how and up to which degree complex patterns are automatically abstracted from an incoming stream of sounds and then used to formulate auditory predictions. Similar processes must operate to extract invariant action-effect rules that then allow formulating reliable action-driven auditory predictions.

In this project, we have investigated action-related prediction along three main lines:

First, action-induced predictions are in one way specially unique: they are precisely time-locked to an externally observable event, i.e., the motor act. We have taken advantage of this fact to be able to observe brain activity coding for sensory predictions and study it in detail. We have achieved this by examining brain responses elicited when a self-initiated sound is unexpectedly omitted, thereby unmasking underlying prediction activity. This group of studies form what we refer to as the omission line.

In a second line of studies, we have investigated the effects of action-driven prediction on the processing of self-initiated sounds. In these studies, we generally compare responses elicited by self-initiated sounds to responses elicited by the same sounds when they are not self-initiated. In particular, we have closely examined the claim that the suppression of the auditory N1 component of the event-related brain potential to self-initiated sounds reflects predictive modeling processes and tried to factor out alternative explanations. Moreover, we have compared action-driven prediction effects to sensory-driven prediction effects combining paradigms from these different lines and exploring our hypothesis of common principles for prediction effects arising from different sources.

Finally, one of the functions that are often assigned to the self-initiation suppression effects is to be able to differentiate the consequences of own actions from those of others. However, there is actually little direct evidence unequivocally linking these two things. In the last of our action-related prediction lines, the agency line, we investigate the relationship between action-driven predictions and the sense of agency. Specifically, in these studies we investigate whether N1-suppression effects accompany the feeling of having caused the sound and whether there is a causal relationship between these two phenomena.