Carmen Weiss

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

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

Roughness perception during the rubber hand illusion.

Watching a rubber hand being stroked by a paintbrush while feeling identical stroking of ones own occluded hand can create a compelling illusion that the seen hand becomes part of ones own body. It has been suggested that this so-called rubber hand illusion (RHI) does not simply reflect a bottom-up multisensory integration process but that the illusion is also modulated by top-down, cognitive factors. Here we investigated for the first time whether the conceptual interpretation of the sensory quality of the visuotactile stimulation in terms of roughness can influence the occurrence of the illusion and vice versa, whether the presence of the RHI can modulate the perceived sensory quality of a given tactile stimulus (i.e., in terms of roughness). We used a classical RHI paradigm in which participants watched a rubber hand being stroked by either a piece of soft or rough fabric while they received synchronous or asynchronous tactile stimulation that was either congruent or incongruent with respect to the sensory quality of the material touching the rubber hand. (In)congruencies between the visual and tactile stimulation did neither affect the RHI on an implicit level nor on an explicit level, and the experience of the RHI in turn did not cause any modulations of the felt sensory quality of touch on participants own hand. These findings first suggest that the RHI seems to be resistant to top-down knowledge in terms of a conceptual interpretation of tactile sensations. Second, they argue against the hypothesis that participants own hand tends to disappear during the illusion and that the rubber hand actively replaces it.

When sounds become actions: Higher-order representation of newly learned action sounds in the human motor system

In the absence of visual information, our brain is able to recognize the actions of others by representing their sounds as a motor event. Previous studies have provided evidence for a somatotopic activation of the listeners motor cortex during perception of the sound of highly familiar motor acts. The present experiments studied (a) how the motor system is activated by action-related sounds that are newly acquired and (b) whether these sounds are represented with reference to extrinsic features related to action goals rather than with respect to lower-level intrinsic parameters related to the specific movements. TMS was used to measure the correspondence between auditory and motor codes in the listeners motor system. We compared the corticomotor excitability in response to the presentation of auditory stimuli void of previous motor meaning before and after a short training period in which these stimuli were associated with voluntary actions. Novel cross-modal representations became manifest very rapidly. By disentangling the representation of the muscle from that of the actions goal, we further showed that passive listening to newly learnt action-related sounds activated a precise motor representation that depended on the variable contexts to which the individual was exposed during testing. Our results suggest that the human brain embodies a higher-order audio-visuo-motor representation of perceived actions, which is muscle-independent and corresponds to the goals of the action.

The self in social interactions: sensory attenuation of auditory action effects is stronger in interactions with others.

The experience of oneself as an agent not only results from interactions with the inanimate environment, but often takes place in a social context. Interactions with other people have been suggested to play a key role in the construal of self-agency. Here, we investigated the influence of social interactions on sensory attenuation of action effects as a marker of pre-reflective self-agency. To this end, we compared the attenuation of the perceived loudness intensity of auditory action effects generated either by oneself or another person in either an individual, non-interactive or interactive action context. In line with previous research, the perceived loudness of self-generated sounds was attenuated compared to sounds generated by another person. Most importantly, this effect was strongly modulated by social interactions between self and other. Sensory attenuation of self- and other-generated sounds was increased in interactive as compared to the respective individual action contexts. This is the first experimental evidence suggesting that pre-reflective self-agency can extend to and is shaped by interactions between individuals.

Agency in the sensorimotor system and its relation to explicit action awareness.

People generally have a strong and immediate intuition whether they are the author of an action or not. Nevertheless, recent psychological studies focused on situations of ambiguous agency. These studies concluded that agency is an inference rather than a direct perception, and is, at least sometimes, illusory. Moreover, shared representations of executed and merely observed actions within the sensorimotor system pose a challenge to the idea that a sense of agency can be grounded within that system. Here, we sought to investigate whether the human motor system is indeed sensitive to whether observed actions are linked to agency or not. In addition, we investigated whether the mere observation of an action has comparable effects on low-level, sensorimotor measures of agency, and on high-level, explicit representations of agency. To this end, we instructed participants to make simple manual movements, and manipulated the temporal correspondence between the movement that they made and the movement that they observed. Motor-evoked potentials to single-pulse TMS were taken as a low-level, sensorimotor measure of agency. To assess explicit representations of agency, participants verbally judged whether or not the observed movement temporally corresponded to the movement they executed. The results showed that corticospinal excitability varied with the degree of temporal correspondence of the executed and observed movements. Moreover, explicit agency judgments could be predicted from corticospinal excitability. This suggests that explicit judgments of agency could be directly based on information within the sensorimotor system.

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

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