The social or joint Simon effect has been developed to investigate how and to what extent people mentally represent their own and other persons' action/task and how these cognitive representations influence an individual's own behavior when interacting with another person. Here, we provide a review of the available evidence and theoretical frameworks. Based on this review, we suggest a comprehensive theory that integrates aspects of earlier approaches-the Referential Coding Account. This account provides an alternative to the social interpretation of the (joint) go-nogo Simon effect (aka the social Simon effect) and is able to integrate seemingly opposite findings on joint action.
Beside language, space is to date the most widely recognized lateralized systems. For example, it has been shown that even mental representations of space and the spatial representation of abstract concepts display lateralized characteristics. For the most part, this body of literature describes space as distal or something outside of the observer or actor. What has been strangely absent in the literature on the whole and specifically in the spatial literature until recently is the most proximal space imaginable - the body. In this review, we will summarize three strands of literature showing laterality in body representations. First, evidence of hemispheric asymmetries in body space in health and, second in body space in disease will be examined. Third, studies pointing to differential contributions of the right and left hemisphere to illusory body (space) will be summarized. Together these studies show hemispheric asymmetries to be evident in body representations at the level of simple somatosensory and proprioceptive representations. We propose a novel working hypothesis, whereby neural systems dedicated to processing action-oriented information about one's own body space may ontogenetically serve as a template for the perception of the external world.
Joint actions require the integration of simultaneous self- and other-related behaviour. Here, we investigated whether this function is underpinned by motor simulation, that is the capacity to represent a perceived action in terms of the neural resources required to execute it. This was tested in a music performance experiment wherein on-line brain stimulation (double-pulse transcranial magnetic stimulation, dTMS) was employed to interfere with motor simulation. Pianists played the right-hand part of piano pieces in synchrony with a recording of the left-hand part, which had (Trained) or had not (Untrained) been practiced beforehand. Training was assumed to enhance motor simulation. The task required adaptation to tempo changes in the left-hand part that, in critical conditions, were preceded by dTMS delivered over the right primary motor cortex. Accuracy of tempo adaptation following dTMS or sham stimulations was compared across Trained and Untrained conditions. Results indicate that dTMS impaired tempo adaptation accuracy only during the perception of trained actions. The magnitude of this interference was greater in empathic individuals possessing a strong tendency to adopt others perspectives. These findings suggest that motor simulation provides a functional resource for the temporal coordination of ones own behaviour with others in dynamic social contexts.
Groove is often described as a musical quality that can induce movement in a listener. This study examines the effects of listening to groove music on corticospinal excitability. Musicians and non-musicians listened to high-groove music, low-groove music, and spectrally matched noise, while receiving single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex either on-beat or off-beat. We examined changes in the amplitude of the motor-evoked potentials (MEPs), recorded from hand and arm muscles, as an index of activity within the motor system. Musicians and non-musicians rated groove similarly. MEP results showed that high-groove music modulated corticospinal excitability, whereas no difference occurred between low-groove music and noise. More specifically, musicians MEPs were larger with high-groove than low-groove music, and this effect was especially pronounced for on-beat compared to off-beat pulses. These results indicate that high-groove music increasingly engages the motor system, and the temporal modulation of corticospinal excitability with the beat could stem from tight auditory-motor links in musicians. Conversely, non-musicians MEPs were smaller for high-groove than low-groove music, and there was no effect of on- versus off-beat pulses, potentially stemming from suppression of overt movement. In sum, high-groove music engages the motor system, and previous training modulates how listening to music with a strong groove activates the motor system.
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.
Recent studies indicate that the primary somatosensory cortex (S1) is active not only when touch is physically perceived but also when it is merely observed to be experienced by another person. This social responsivity of S1 has important implications for our understanding of S1 functioning. However, S1 activity during touch observation has not been characterized in great detail to date. We focused on two features of the S1 functional architecture during touch observation, namely the topographical arrangement of index and middle finger receptive fields (RFs), and their dynamic shrinkage during concurrent activation. Both features have important implications for human behavior. We conducted two fMRI studies at 7 T, one where touch was physically perceived, and one where touch was observed. In the two experiments, participants either had their index finger and/or middle finger stimulated using paintbrushes, or just observed similar touch events on video. Our data show that observing and physically experiencing touch elicits overlapping activity changes in S1. In addition, observing touch to the index finger or the middle finger alone evoked topographically arranged activation foci in S1. Importantly, when co-activated, the index and middle finger RFs not only shrank during physical touch perception, but also during touch observation. Our data, therefore, indicate a similarity between the functional architecture of S1 during touch observation and physical touch perception with respect to single-digit topography and RF shrinkage. These results may allow the tentative conclusion that even primary somatosensory experiences, such as physical touch perception, can be shared amongst individuals.
Generating predictions during action observation is essential for efficient navigation through our social environment. With age, the sensitivity in action prediction declines. In younger adults, the action observation network (AON), consisting of premotor, parietal and occipitotemporal cortices, has been implicated in transforming executed and observed actions into a common code. Much less is known about age-related changes in the neural representation of observed actions. Using fMRI, the present study measured brain activity in younger and older adults during the prediction of temporarily occluded actions (figure skating elements and simple movement exercises). All participants were highly familiar with the movement exercises whereas only some participants were experienced figure skaters. With respect to the AON, the results confirm that this network was preferentially engaged for the more familiar movement exercises. Compared to younger adults, older adults recruited visual regions to perform the task and, additionally, the hippocampus and caudate when the observed actions were familiar to them. Thus, instead of effectively exploiting the sensorimotor matching properties of the AON, older adults seemed to rely predominantly on the visual dynamics of the observed actions to perform the task. Our data further suggest that the caudate played an important role during the prediction of the less familiar figure skating elements in better-performing groups. Together, these findings show that action prediction engages a distributed network in the brain, which is modulated by the content of the observed actions and the age and experience of the observer.
Human behavior is comprised of an interaction between intentionally driven actions and reactions to changes in the environment. Existing data are equivocal concerning the question of whether these two action systems are independent, involve different brain regions, or overlap. To address this question we investigated whether the degree to which the voluntary action system is activated at the time of stimulus onset predicts reaction times to external stimuli. We recorded event-related potentials while participants prepared and executed left- or right-hand voluntary actions, which were occasionally interrupted by a stimulus requiring either a left- or right-hand response. In trials where participants successfully performed the stimulus-driven response, increased voluntary motor preparation was associated with faster responses on congruent trials (where participants were preparing a voluntary action with the same hand that was then required by the target stimulus), and slower responses on incongruent trials. This suggests that early hand-specific activity in medial frontal cortex for voluntary action trials can be used by the stimulus-driven system to speed responding. This finding questions the clear distinction between voluntary and stimulus-driven action systems.
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.
This study examines the neurocognitive mechanisms underlying the sense of agency, that is, the experience of causing and controlling events in our environment. Specifically, we tested the hypothesis that the sense of agency depends on an optimal integration of different anticipatory signals, generated by motor and nonmotor systems. An established marker of pre-reflective agency experience is the suppression of cortical responses to actively generated feedback as compared to passively observed feedback, which was measured here by event-related potentials (ERPs). Sensory expectations based on motor-related and unrelated signals were induced by varying the probabilistic contingency between action and feedback, and by priming the feedback prior to the action. Moreover, simultaneous conscious agency judgments were assessed. A reduction of visual N1 response was found to self- as compared to externally generated feedback. In addition, the N1 was modulated by accurate anticipations based on prime stimuli, independent of the precision of motor predictions. Conscious agency judgments, in contrast, were enhanced by prime stimuli only in situations where no precise motor predictions of the action feedback were available. These results indicate that anticipatory signals arising from motor and nonmotor systems are integrated differently depending on the level of agency processing. Our findings suggest that, at a pre-reflective level, the brains agency system relies on both embodied signals and nonmotor sensory expectations. At higher cognitive levels, motor and nonmotor cues are weighted differently depending on their relative reliability in a given context, thereby providing a basis for robust agentive self-awareness.
A large body of evidence suggests that action execution and action observation share a common representational domain. To date, little is known about age-related changes in these action representations that are assumed to support various abilities such as the prediction of observed actions. The purpose of the present study was to investigate (a) how age affects the ability to predict the time course of observed actions; and (b) whether and to what extent sensorimotor expertise attenuates age-related declines in prediction performance. In a first experiment, older adults predicted the time course of familiar everyday actions less precisely than younger adults. In a second experiment, younger and older figure skating experts as well as age-matched novices were asked to predict the time course of figure skating elements and simple movement exercises. Both young age and sensorimotor expertise had a positive influence on prediction performance of figure skating elements. The expertise-related benefit did not show a transfer to movement exercises. Together, the results suggest a specific decline of action representations in the aging mind. However, extensive sensorimotor experience seems to enable experts to represent actions from their domain of expertise more precisely even in older age.
Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and-the to-date largely neglected group of-mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants handedness and the hand used for bisection exerted a significant influence on participants estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.
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.
The field of neuroaesthetics attracts attention from neuroscientists and artists interested in the neural underpinnings of esthetic experience. Though less studied than the neuroaesthetics of visual art, dance neuroaesthetics is a particularly rich subfield to explore, as it is informed not only by research on the neurobiology of aesthetics, but also by an extensive literature on how action experience shapes perception. Moreover, it is ideally suited to explore the embodied simulation account of esthetic experience, which posits that activation within sensorimotor areas of the brain, known as the action observation network (AON), is a critical element of the esthetic response. In the present study, we address how observers esthetic evaluation of dance is related to their perceived physical ability to reproduce the movements they watch. Participants underwent functional magnetic resonance imaging while evaluating how much they liked and how well they thought they could physically replicate a range of dance movements performed by professional ballet dancers. We used parametric analyses to evaluate brain regions that tracked with degree of liking and perceived physical ability. The findings reveal strongest activation of occipitotemporal and parietal portions of the AON when participants view movements they rate as both esthetically pleasing and difficult to reproduce. As such, these findings begin to illuminate how the embodied simulation account of esthetic experience might apply to watching dance, and provide preliminary evidence as to why some people find enjoyment in an evening at the ballet.
In the standard Simon task, participants carry out spatially defined responses to non-spatial stimulus attributes. Responses are typically faster when stimulus location and response location correspond. This effect disappears when a participant responds to only one of the two stimuli and reappears when another person carries out the other response. This social Simon effect (SSE) has been considered as providing an index for action co-representation. Here, we investigated whether joint-action effects in a social Simon task involve mechanisms of action co-representation, as measured by the amount of incorporation of another persons action. We combined an auditory social Simon task with a manipulation of the sense of ownership of another persons hand (rubber hand illusion). If the SSE is established by action co-representation, then the incorporation of the other persons hand into ones own body representation should increase the SSE (synchronous?>?asynchronous stroking). However, we found the SSE to be smaller in the synchronous as compared to the asynchronous stroking condition (Experiment 1), suggesting that the SSE reflects the separation of spatial action events rather than the integration of the other persons action. This effect is independent of the active involvement (Experiment 2) and the presence of another person (Experiment 3). These findings suggest that the "social" Simon effect is not really social in nature but is established when an interaction partner produces events that serve as a spatial reference for ones own actions.
The ability to recognize oneself in voluntary action is called the sense of agency and refers to the experience of causing ones own actions and their sensory consequences. This form of self-awareness is important not only for motor control but also for social interactions and the ascription of causal responsibility. Here, we examined the sense of agency at early and prereflective stages of action perception using ERPs. Subjects performed a visual forced-choice response task in which action effects were either caused by the subject or by the computer. In addition, to modulate the conscious experience of agency, action effects were subliminally primed by the presentation of congruent, incongruent, or neutral effect stimuli before the action. First, we observed sensorimotor attenuation in the visual ERP selectively for self-generated action effects. That is, the N1 component, a negative deflection around 100 msec after a visual stimulus, was smaller in amplitude for visual effects caused by the subject as compared with effects caused by the computer. Second, congruent effect priming enhanced the explicit judgment of agency and further reduced the N1 amplitude for self-generated effects, although effect primes were not consciously processed. Taken together, these results provide evidence of a top-down modulation of sensory processing of action effects by prior effect information and support the neurophysiological mechanism of sensorimotor attenuation as underlying self-registration in action. Our findings suggest that both efferent information and prior thoughts about the action consequence provide important cues for a prereflective form of the experience of being an agent.
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.
It is well documented that in the first year after birth, infants are able to identify self-performed actions. This ability has been regarded as the basis of conscious self-perception. However, it is not yet known whether infants are also sensitive to aspects of the self when they cannot control the sensory feedback by means of self-performed actions. Therefore, we investigated the contribution of visual-tactile contingency to self-perception in infants. In Experiment 1, 7- and 10-month-olds were presented with two video displays of lifelike baby doll legs. The infants left leg was stroked contingently with only one of the video displays. The results showed that 7- and 10-month-olds looked significantly longer at the contingent display than at the non-contingent display. Experiment 2 was conducted to investigate the role of morphological characteristics in contingency detection. Ten-month-olds were presented with video displays of two neutral objects (i.e., oblong wooden blocks of approximately the same size as the doll legs) being stroked in the same way as in Experiment 1. No preference was found for either the contingent or the non-contingent display but our results confirm a significant decrease in looking time to the contingent display compared to Experiment 1. These results indicate that detection of visual-tactile contingency as one important aspect of self-perception is present very early in ontogeny. Furthermore, this ability appears to be limited to the perception of objects that strongly resemble the infants body, suggesting an early sensitivity to the morphology of ones own body.
Linking observed and executable actions appears to be achieved by an action observation network (AON), comprising parietal, premotor, and occipitotemporal cortical regions of the human brain. AON engagement during action observation is thought to aid in effortless, efficient prediction of ongoing movements to support action understanding. Here, we investigate how the AON responds when observing and predicting actions we cannot readily reproduce before and after visual training. During pre- and posttraining neuroimaging sessions, participants watched gymnasts and wind-up toys moving behind an occluder and pressed a button when they expected each agent to reappear. Between scanning sessions, participants visually trained to predict when a subset of stimuli would reappear. Posttraining scanning revealed activation of inferior parietal, superior temporal, and cerebellar cortices when predicting occluded actions compared to perceiving them. Greater activity emerged when predicting untrained compared to trained sequences in occipitotemporal cortices and to a lesser degree, premotor cortices. The occipitotemporal responses when predicting untrained agents showed further specialization, with greater responses within body-processing regions when predicting gymnasts movements and in object-selective cortex when predicting toys movements. The results suggest that (1) select portions of the AON are recruited to predict the complex movements not easily mapped onto the observers body and (2) greater recruitment of these AON regions supports prediction of less familiar sequences. We suggest that the findings inform both the premotor model of action prediction and the predictive coding account of AON function.
Analogously to the visual system, somatosensory processing may be segregated into two streams, with the body constituting either part of the action system or a perceptual object. Experimental studies with participants free from neurological disease which test this hypothesis are rare, however. The present study explored the contributions of the two putative streams to a task that requires participants to estimate the spatial properties of their own body. Two manipulations from the visuospatial literature were included. First, participants were required to point either backward towards pre-defined landmarks on their own body (egocentric reference frame) or to a forward projection of their own body (allocentric representation). Second, a manipulation of movement mode was included, requiring participants to perform pointing movements either immediately, or after a fixed delay, following instruction. Results show that accessing an allocentric representation of ones own body results in performance changes. Specifically, the spatial bias shown to exist for body space when pointing backward at ones own body disappears when participants are requested to mentally project their body to a pre-defined location in front space. Conversely, delayed execution of pointing movements does not result in performance changes. Altogether, these findings provide support for a constrained dual stream hypothesis of somatosensory processing and are the first to show similarities in the processing of body space and peripersonal space.
The systematic association of an action that a person performs with its sensory effects is thought to attenuate that persons perception of the effect of the action. However, whether learned sensorimotor contingencies truly affect perception, rather than just inducing a response bias, has yet to be determined. The experiment presented in this article comprised two parts: an action-effect association phase and a test phase, during which the actions perceptual effects were tested. During the association phase, specific actions (left-key and right-key presses) were associated with specific visual effects (tilted Gabor patches). In the test phase, participants left-key presses and right-key presses triggered the onset of a low-contrast tilted Gabor patch in 50% of trials (no stimulus was presented on the remaining 50% of trials). Participants were required to report the presence or absence of this tilted Gabor patch. Our results showed that participants sensitivity (d) to the Gabor patches was reduced by 10% when the patches were triggered by the action they had previously been associated with. This finding indicates that a persons action does not induce a response bias (c), but changes the perception (d) of the learned action effect.
Ideomotor theory of human action control proposes that activation of a motor representation can occur either through internally-intended or externally-perceived actions. Critically, sometimes these alternatives of eliciting a motor response may be conflicting, for example, when intending one action and perceiving another, necessitating the recruitment of enhanced action-control to avoid motor mimicry. Based on previous neuroimaging evidence, suggesting that reduced mimicry is associated with self-related processing, we aimed to experimentally enhance these action-control mechanisms during motor contagion by inducing self-focus. In two within-subjects experiments, participants had to enforce their action intention against an external motor contagion tendency under heightened and normal self-focus. During high self-focus participants showed reduced motor mimicry, induced either by mirror self-observation or self-referential judgments. This indicates that a self-focus provoking situation can enhance online action-control mechanisms, needed to resist unintentional motor contagion tendencies and thereby enables a modulation of automatic mirroring responses.
A difference in the perception of extrapersonal space has been shown to exist between dextrals and sinistrals. On the classical line bisection task, this difference is evident in a greater left bias for dextrals compared to sinistrals. Different modalities and regions of space can be affected. However, it has not yet been investigated whether a systematic bias also exists for the perception of personal or body space. We investigated this by using three tasks which assess different aspects of personal space in an implicit and explicit way. These tasks were performed by strongly right-handed (dextrals), strongly left-handed (sinistrals) and mixed-handed participants. First, a task of pointing to three areas of ones own body without the use of visual information showed dextrals to have an asymmetric estimation of their body. In right hemispace, dextrals pointing was at a greater distance from the midsagittal plane compared to pointing in left hemispace. No such asymmetry was present for sinistrals, while mixed-handers performance was intermediate to that of strong right- and strong left-handers. Second, a task of recovering circular patches from their body surface whilst blindfolded also showed superior performance of sinistrals compared to dextrals. On these two tasks, there was also a moderate relationship between handedness scores and performance measures. Third, a computer-based task of adjusting scaled body-outline-halves showed no handedness differences. Overall, these findings suggest handedness differences in the implicit but not explicit representation of ones own body space. Possible mechanisms underlying the handedness differences shown for the implicit tasks are a stronger lateralization or a greater activation imbalance for dextrals and/or greater access to right hemispheric functions, such as an "up-to-date body" representation, by sinistrals. In contrast, explicit measures of how body space is represented may not be affected due to their relying on a different processing pathway.
Numerous studies suggest that both self-generated and observed actions of others activate overlapping neural networks, implying a shared, agent-neutral representation of self and other. Contrary to the shared representation hypothesis, we recently showed that the human motor system is not neutral with respect to the agent of an observed action [Schütz-Bosbach, S., Mancini, B., Aglioti, S. M., & Haggard, P. Self and other in the human motor system. Current Biology, 16, 1830-1834, 2006]. Observation of actions attributed to another agent facilitated the motor system, whereas observation of identical actions linked to the self did not. Here we investigate whether the absence of motor facilitation for observing ones own actions reflects a specific process of cortical inhibition associated with self-representation. We analyzed the duration of the silent period induced by transcranial magnetic stimulation of the motor cortex in active muscles as an indicator of motor inhibition. We manipulated whether an observed action was attributed to another agent, or to the subjects themselves, using a manipulation of body ownership on the basis of the rubber hand illusion. Observation of actions linked to the self led to longer silent periods than observation of a static hand, but the opposite effect occurred when observing identical actions attributed to another agent. This finding suggests a specific inhibition of the motor system associated with self-representation. Cortical suppression for actions linked to the self might prevent inappropriate perseveration within the motor system.
The "body image" is a putative mental representation of ones own body, including structural and geometric details, as well as the more familiar visual and affective aspects. Very little research has investigated how we learn the structure of our own body, with most researchers emphasising the canonical visual representation of the body when we look at ourselves in a mirror. Here, we used non-visual self-touch in healthy participants to investigate the possibility that primary sensorimotor experience may influence cognitive representations of ones own body structure. Participants used the fingers of one hand (the active hand), to touch the fingers of the other (the passive hand). A conflict between the experience of the active and passive hand was introduced by experimenter interleaving their fingers with the fingers of the participants passive hand. This led to the active hand experiencing that it touched more fingers than the passive hand felt it was being touched by. The effects on representation of body structure were assessed using an implicit measure based on Kinsbourne and Warringtons in-between task. We found an underestimation of the number of fingers in the central part of the hand specifically linked to the experience of self-touch. This pattern of results corresponds to the experience of the passive hand, but not the active hand. Nevertheless, comparable reorganisation of fingers within the hand representation was found for both active and passive hands. We show that primary sensorimotor experience can modify the representation of body structure. This modification is driven by the passive experience of being touched, rather than by the active experience of touching. We believe this is the first experimental study of effects of self-touch on the mental representation of the body.
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.
The human tendency to imitate gestures performed by conspecifics is automatic in nature. However, whether this automatic imitation can be considered as a true imitative phenomenon or only as a special instance of spatial compatibility is still being debated. New evidence suggests that automatic imitation, otherwise known as imitative compatibility, shall be considered as a phenomenon that operates independently from spatial compatibility. So far there are only a few investigations directly aimed at identifying the neural structures dedicated to this process. In the present study, we applied double-pulse transcranial magnetic stimulation (TMS) over the parietal opercula to further investigate the role of these regions in coding imitative compatibility. We found that a temporary disruption of parietal opercula caused the reduction of the imitative compatibility relative to the sham condition. In particular, the TMS interference with the parietal operculas activity modulated the imitative compatibility but not the spatial compatibility, suggesting that these two processes are likely to be independent.
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.
Sensory attenuation refers to the observation that self-generated stimuli are attenuated, both in terms of their phenomenology and their cortical response compared to the same stimuli when generated externally. Accordingly, it has been assumed that sensory attenuation might help individuals to determine whether a sensory event was caused by themselves or not. In the present study, we investigated whether this dependency is reciprocal, namely whether sensory attenuation is modulated by prior beliefs of authorship. Participants had to judge the loudness of auditory effects that they believed were either self-generated or triggered by another person. However, in reality, the sounds were always triggered by the participants actions. Participants perceived the tones loudness attenuated when they believed that the sounds were self-generated compared to when they believed that they were generated by another person. Sensory attenuation is considered to contribute to the emergence of peoples belief of authorship. Our results suggest that sensory attenuation is also a consequence of prior belief about the causal link between an action and a sensory change in the environment.
Observing another person being touched activates our own somatosensory system. Whether the primary somatosensory cortex (S1) is also activated during the observation of passive touch, and which subregions of S1 are responsible for self- and other-related observed touch is currently unclear. In our study, we first aimed to clarify whether observing passive touch without any action component can robustly increase activity in S1. Secondly, we investigated whether S1 activity only increases when touch of others is observed, or also when touch of ones own body is observed. We were particularly interested in which subregions of S1 are responsible for either process. We used functional magnetic resonance imaging at 7 Tesla to measure S1 activity changes when participants observed videos of their own or anothers hand in either egocentric or allocentric perspective being touched by different pieces of sandpaper. Participants were required to judge the roughness of the different sandpaper surfaces. Our results clearly show that S1 activity does increase in response to observing passive touch, and that activity changes are localized in posterior but not in anterior parts of S1. Importantly, activity increases in S1 were particularly related to observing another person being touched. Self-related observed touch, in contrast, caused no significant activity changes within S1. We therefore assume that posterior but not anterior S1 is part of a system for sharing tactile experiences with others.
Predicting the actions of other individuals is crucial for our daily interactions. Recent evidence suggests that the prediction of object-directed arm and full-body actions employs the dorsal premotor cortex (PMd). Thus, the neural substrate involved in action control may also be essential for action prediction. Here, we aimed to address this issue and hypothesized that disrupting the PMd impairs action prediction. Using fMRI-guided coil navigation, rTMS (five pulses, 10?Hz) was applied over the left PMd and over the vertex (control region) while participants observed everyday actions in video clips that were transiently occluded for 1?s. The participants detected manipulations in the time course of occluded actions, which required them to internally predict the actions during occlusion. To differentiate between functional roles that the PMd could play in prediction, rTMS was either delivered at occluder-onset (TMS-early), affecting the initiation of action prediction, or 300?ms later during occlusion (TMS-late), affecting the maintenance of an ongoing prediction. TMS-early over the left PMd produced more prediction errors than TMS-early over the vertex. TMS-late had no effect on prediction performance, suggesting that the left PMd might be involved particularly during the initiation of internally guided action prediction but may play a subordinate role in maintaining ongoing prediction. These findings open a new perspective on the role of the left PMd in action prediction which is in line with its functions in action control and in cognitive tasks. In the discussion, the relevance of the left PMd for integrating external action parameters with the observers motor repertoire is emphasized. Overall, the results are in line with the notion that premotor functions are employed in both action control and action observation.
Patients with obsessive-compulsive disorder (OCD) often lack the experience of action completion and have altered feelings of agency. This might depend on the integrity of predictions of action outcomes generated by forward models of the motor system. Such motor predictions are critical for inhibitory gating of actions and their consequences. Therefore, it was hypothesized that OCD patients show compromised forward model mechanisms.
The capacity to distinguish between ones own and others behavior is a cognitive prerequisite for successful joint action. We employed a musical joint action task to investigate how the brain achieves this distinction. Pianists performed the right-hand part of piano pieces, previously learned bimanually, while the complementary left-hand part either was not executed or was (believed to be) played by a co-performer. This experimental setting served to induce a co-representation of the left-hand part reflecting either the self or the co-performer. Single-pulse transcranial magnetic stimulation was applied to the right primary motor cortex and motor-evoked potentials (MEPs) were recorded from the resting left forearm. Results show that corticospinal excitability was modulated by whether the representation of the left hand was associated with the self or the other, with the MEP amplitude being low and high, respectively. This result remained unchanged in a separate session where participants could neither see nor hear the other but still infer his presence by means of contextual information. Furthermore, the amplitude of MEPs associated with co-performer presence increased with pianists self-reported empathy. Thus, the sociality of the context modulates action attribution at the level of the motor control system.
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