Localizing apraxia in corticobasal syndrome: a morphometric MRI study.

Apraxia localization has relied on voxel-based, lesion-symptom mapping studies in left hemisphere stroke patients. Studies on the neural substrates of different manifestations of apraxia in neurodegenerative disorders are scarce. The primary aim of this study was to look into the neural substrates of different manifestations of apraxia in a cohort of corticobasal syndrome patients (CBS) by use of cortical thickness. Twenty-six CBS patients were included in this cross-sectional study. The Goldenberg apraxia test (GAT) was applied. 3D-T1-weighted images were analyzed via the automated recon-all Freesurfer version 6.0 pipeline. Vertex-based multivariate General Linear Model analysis was applied to correlate GAT scores with cortical thickness. Deficits in imitation of meaningless gestures correlated with bilateral superior parietal atrophy, extending to the angular and supramarginal gyri, particularly on the left. Finger imitation relied predominantly on superior parietal lobes, whereas the left angular and supramarginal gyri, in addition to superior parietal lobes, were critical for hand imitation. The widespread bilateral clusters of atrophy in CBS related to apraxia indicate different pathophysiological mechanisms mediating praxis in neurodegenerative disorders compared to vascular lesions, with implications both for our understanding of praxis and for the rehabilitation approaches of patients with apraxia.

Boosting interpersonal emotion regulation through facial imitation: functional neuroimaging foundations.

Empathic function, which is primarily manifested by facial imitation, is believed to play a pivotal role in interpersonal emotion regulation for mood reinstatement. To explore this association and its neural substrates, we performed a questionnaire survey (study l) to identify the relationship between empathy and interpersonal emotion regulation; and a task-mode fMRI study (study 2) to explore how facial imitation, as a fundamental component of empathic processes, promotes the interpersonal emotion regulation effect. Study 1 showed that affective empathy was positively correlated with interpersonal emotion regulation. Study 2 showed smaller negative emotions in facial imitation interpersonal emotion regulation (subjects imitated experimenter's smile while followed the interpersonal emotion regulation guidance) than in normal interpersonal emotion regulation (subjects followed the interpersonal emotion regulation guidance) and Watch conditions. Mirror neural system (e.g. inferior frontal gyrus and inferior parietal lobe) and empathy network exhibited greater activations in facial imitation interpersonal emotion regulation compared with normal interpersonal emotion regulation condition. Moreover, facial imitation interpersonal emotion regulation compared with normal interpersonal emotion regulation exhibited increased functional coupling from mirror neural system to empathic and affective networks during interpersonal emotion regulation. Furthermore, the connectivity of the right orbital inferior frontal gyrus-rolandic operculum lobe mediated the association between the accuracy of facial imitation and the interpersonal emotion regulation effect. These results show that the interpersonal emotion regulation effect can be enhanced by the target's facial imitation through increased functional coupling from mirror neural system to empathic and affective neural networks.

Automatic imitation in school-aged children.

Children imitate others for different reasons: To learn from others and to reach social goals such as affiliation or prosociality. So far, imitative acts have been measured using diverging methods in children and adults. Here, we investigated whether school-aged children's imitation can be measured via their automatic imitation with a classical imitation-inhibition task (Brass et al., 2000) as has been used in adults. To this end, we measured automatic imitation in N=94 7-8-year-olds and N=10 adults. The results were similar in children and adults: Observing actions that are incongruent with participants' actions interferes with their responses resulting in increased reaction times and error rates. This shows that assessing automatic imitation via the imitation-inhibition task is feasible in children, and creates the basis for future studies to compare the behaviour of different age groups with the same imitation task.

Are there dedicated neural mechanisms for imitation? A study of grist and mills.

Are there brain regions that are specialized for the execution of imitative actions? We compared two hypotheses of imitation: the mirror neuron system (MNS) hypothesis predicts frontal and parietal engagement which is specific to imitation, while the Grist-Mills hypothesis predicts no difference in brain activation between imitative and matched non-imitative actions. Our delayed imitation fMRI paradigm included two tasks, one where correct performance was defined by a spatial rule and another where it was defined by an item-based rule. For each task, participants could learn a sequence from a video of a human hand performing the task, from a matched "Ghost" condition, or from text instructions. When participants executed actions after seeing the Hand demonstration (compared to Ghost and Text demonstrations), no activation differences occurred in frontal or parietal regions; rather, activation was localized primarily to occipital cortex. This adds to a growing body of evidence which indicates that imitation-specific responses during action execution do not occur in canonical mirror regions, contradicting the mirror neuron system hypothesis. However, activation differences did occur between action execution in the Hand and Ghost conditions outside MNS regions, which runs counter to the Grist-Mills hypothesis. We conclude that researchers should look beyond these hypotheses as well as classical MNS regions to describe the ways in which imitative actions are implemented by the brain.

Differential responses in the mirror neuron system during imitation of individual emotional facial expressions and association with autistic traits.

The mirror neuron system (MNS), including the inferior frontal gyrus (IFG), inferior parietal lobule (IPL) and superior temporal sulcus (STS) plays an important role in action representation and imitation and may be dysfunctional in autism spectrum disorder (ASD). However, it's not clear how these three regions respond and interact during the imitation of different basic facial expressions and whether the pattern of responses is influenced by autistic traits. Thus, we conducted a natural facial expression (happiness, angry, sadness and fear) imitation task in 100 healthy male subjects where expression intensity was measured using facial emotion recognition software (FaceReader) and MNS responses were recorded using functional near-infrared spectroscopy (fNIRS). Autistic traits were measured using the Autism Spectrum Quotient questionnaire. Results showed that imitation of happy expressions produced the highest expression intensity but a small deactivation in MNS responses, suggesting a lower processing requirement compared to other expressions. A cosine similarity analysis indicated a distinct pattern of MNS responses during imitation of each facial expression with functional intra-hemispheric connectivity between the left IPL and left STS being significantly higher during happy compared to other expressions, while inter-hemispheric connectivity between the left and right IPL differed between imitation of fearful and sad expressions. Furthermore, functional connectivity changes during imitation of each different expression could reliably predict autistic trait scores. Overall, the results provide evidence for distinct patterns of functional connectivity changes between MNS regions during imitation of different emotions which are also associated with autistic traits.

Two-action task, testing imitative social learning in kea (Nestor notabilis).

Social learning is an adaptive way of dealing with the complexity of life as it reduces the risk of trial-and-error learning. Depending on the type of information acquired, and associations formed, several mechanisms within the larger taxonomy of social learning can be distinguished. Imitation is one such process within this larger taxonomy, it is considered cognitively demanding and is associated with high-fidelity response matching. The present study reproduced a 2002 study conducted by Heyes and Saggerson, which successfully illustrated motor imitation in budgerigars (Melopsittacus undulatus). In our study, eighteen kea (Nestor notabilis) that observed a trained demonstrator remove a stopper from a test box (1) took less time from hopping on the box to feeding (response duration) in session one and (2) were faster in making a vertical removal response on the stopper once they hopped on the box (removal latency) in session one than non-observing control group individuals. In contrast to the budgerigars (Heyes and Saggerson, Ani Behav. 64:851-859, 2002) the present study could not find evidence of motor imitation in kea. The results do illustrate, however, that there were strong social effects on exploration rates indicating motivational and attentional shifts. Furthermore, the results may suggest a propensity toward emulation in contrast to motor imitation or alternatively selectivity in the application of imitation.

An active inference model of hierarchical action understanding, learning and imitation.

We advance a novel active inference model of the cognitive processing that underlies the acquisition of a hierarchical action repertoire and its use for observation, understanding and imitation. We illustrate the model in four simulations of a tennis learner who observes a teacher performing tennis shots, forms hierarchical representations of the observed actions, and imitates them. Our simulations show that the agent's oculomotor activity implements an active information sampling strategy that permits inferring the kinematic aspects of the observed movement, which lie at the lowest level of the action hierarchy. In turn, this low-level kinematic inference supports higher-level inferences about deeper aspects of the observed actions: proximal goals and intentions. Finally, the inferred action representations can steer imitative responses, but interfere with the execution of different actions. Our simulations show that hierarchical active inference provides a unified account of action observation, understanding, learning and imitation and helps explain the neurobiological underpinnings of visuomotor cognition, including the multiple routes for action understanding in the dorsal and ventral streams and mirror mechanisms.

Does the threat of COVID-19 modulate automatic imitation?

The tendency to involuntarily imitate the actions of others (automatic imitation) can be modulated by social affiliative cues. Here, we explored whether the disruption to our social lives caused by the COVID-19 pandemic may subsequently influence automatic imitation. Three groups were initially presented a sentence comprehension task that featured either neutral (control), safe or unsafe primes to COVID-19 infection. They then completed an automatic imitation task, where a numeric cue was presented alongside apparent motion of an index or middle finger, which was either compatible or incompatible with the required response. Reaction times were longer for the incompatible compared to compatible trials, and thus demonstrated automatic imitation. However, there was no influence of the primes indicating that automatic imitation was unaffected by the risk of COVID-19. The potential theoretical explanations and practical implications of pathogen avoidance and social bonding incentives are discussed with reference to pandemic events.

Young children use imitation communicatively.

There is growing evidence that children imitate not just to learn from others but also to affiliate socially with them. However, although imitation can convey a wealth of affiliative information to others, it is not yet known whether imitators intend for this to be the case. In particular, we do not know whether children imitate communicatively in some contexts, expending extra effort to make sure that the demonstrator sees their imitation. Here, in two experiments (N = 20 and N = 48, respectively), we tested whether preschool-age children modify their imitation when needed to ensure that the demonstrator sees it. In each trial, children were shown a demonstration. Then, for their response, in one condition a barrier obscured the demonstrator's view of children's imitation unless children raised their arms above the barrier while imitating. In the other condition the demonstrator was able to see children's imitation without any additional effort from children. Results from both experiments showed that children were significantly more likely to imitate with their arms raised when their actions would otherwise be obscured from view. In the second experiment, we also coded for other communicative behaviors (e.g., social smiles, eye contact, showing gestures) and found that children often displayed communicative behaviors while imitating, as expected, in both conditions. Thus, young children actively use imitation communicatively in some contexts.

Training self-other distinction facilitates perspective taking in young children.

People sometimes commit 'egocentric errors', failing to ignore their own perspective when interpreting others' communication. Training imitation-inhibition, when participants perform the opposite action from another person, facilitates subsequent perspective-taking in adults. This study tested whether imitation-inhibition training also facilitates perspective-taking in 3- to 6-year-olds, an age where egocentric perspective may be particularly influential. Children participated in a 10-min imitation-inhibition, imitation, or non-social-inhibition training (white, n = 25 per condition, 33 female, period: 2018-2021), then the communicative-perspective-taking Director task. Training had a significant effect (F(2, 71) = 3.316, p = .042, η2  = .085): on critical trials, the imitation-inhibition-group selected the correct object more often than the other groups. Imitation-inhibition training specifically enhanced the perspective-taking process possibly by highlighting the distinction between self and other.

Orcas remember what to copy: a deferred and interference-resistant imitation study.

Response facilitation has often been portrayed as a "low level" category of social learning, because the demonstrator's action, which is already in the observer's repertoire, automatically triggers that same action, rather than induces the learning of a new action. One way to rule out response facilitation consists of introducing a delay between the demonstrator's behavior and the observer's response to let their possible effects wear off. However, this may not rule out "delayed response facilitation" in which the subject could be continuously "mentally rehearsing" the demonstrated actions during the waiting period. We used a do-as-the-other-did paradigm in two orcas to study whether they displayed cognitive control regarding their production of familiar actions by (1) introducing a delay ranging from 60 to 150 s between observing and producing the actions and (2) interspersing distractor (non-target) actions performed by the demonstrator and by the subjects during the delay period. These two manipulations were aimed at preventing the mental rehearsal of the observed actions during the delay period. Both orcas copied the model's target actions on command after various delay periods, and crucially, despite the presence of distractor actions. These findings suggest that orcas are capable of selectively retrieving a representation of an observed action to generate a delayed matching response. Moreover, these results lend further support to the proposal that the subjects' performance relied not only on a mental representation of the specific actions that were requested to copy, but also flexibly on the abstract and domain general rule requested by the specific "copy command". Our findings strengthen the view that orcas and other cetaceans are capable of flexible and controlled social learning.

Bayesian Disturbance Injection: Robust imitation learning of flexible policies for robot manipulation.

Humans demonstrate a variety of interesting behavioral characteristics when performing tasks, such as selecting between seemingly equivalent optimal actions, performing recovery actions when deviating from the optimal trajectory, or moderating actions in response to sensed risks. However, imitation learning, which attempts to teach robots to perform these same tasks from observations of human demonstrations, often fails to capture such behavior. Specifically, commonly used learning algorithms embody inherent contradictions between the learning assumptions (e.g., single optimal action) and actual human behavior (e.g., multiple optimal actions), thereby limiting robot generalizability, applicability, and demonstration feasibility. To address this, this paper proposes designing imitation learning algorithms with a focus on utilizing human behavioral characteristics, thereby embodying principles for capturing and exploiting actual demonstrator behavioral characteristics. This paper presents the first imitation learning framework, Bayesian Disturbance Injection (BDI), that typifies human behavioral characteristics by incorporating model flexibility, robustification, and risk sensitivity. Bayesian inference is used to learn flexible non-parametric multi-action policies, while simultaneously robustifying policies by injecting risk-sensitive disturbances to induce human recovery action and ensuring demonstration feasibility. Our method is evaluated through risk-sensitive simulations and real-robot experiments (e.g., table-sweep task, shaft-reach task and shaft-insertion task) using the UR5e 6-DOF robotic arm, to demonstrate the improved characterization of behavior. Results show significant improvement in task performance, through improved flexibility, robustness as well as demonstration feasibility.

Automatic imitation of human and computer-generated vocal stimuli.

Observing someone perform an action automatically activates neural substrates associated with executing that action. This covert response, or automatic imitation, is measured behaviourally using the stimulus-response compatibility (SRC) task. In an SRC task, participants are presented with compatible and incompatible response-distractor pairings (e.g., an instruction to say "ba" paired with an audio recording of "da" as an example of an incompatible trial). Automatic imitation is measured as the difference in response times (RT) or accuracy between incompatible and compatible trials. Larger automatic imitation effects have been interpreted as a larger covert imitation response. Past results suggest that an action's biological status affects automatic imitation: Human-produced manual actions show enhanced automatic imitation effects compared with computer-generated actions. Per the integrated theory for language comprehension and production, action observation triggers a simulation process to recognize and interpret observed speech actions involving covert imitation. Human-generated actions are predicted to result in increased automatic imitation because the simulation process is predicted to engage more for actions produced by a speaker who is more similar to the listener. We conducted an online SRC task that presented participants with human and computer-generated speech stimuli to test this prediction. Participants responded faster to compatible than incompatible trials, showing an overall automatic imitation effect. Yet the human-generated and computer-generated vocal stimuli evoked similar automatic imitation effects. These results suggest that computer-generated speech stimuli evoke the same covert imitative response as human stimuli, thus rejecting predictions from the integrated theory of language comprehension and production.

Reaction Time "Mismatch Costs" Change with the Likelihood of Stimulus-Response Compatibility.

Dyadic interactions require dynamic correspondence between one's own movements and those of the other agent. This mapping is largely viewed as imitative, with the behavioural hallmark being a reaction-time cost for mismatched actions. Yet the complex motor patterns humans enact together extend beyond direct-matching, varying adaptively between imitation, complementary movements, and counter-imitation. Optimal behaviour requires an agent to predict not only what is likely to be observed but also how that observed action will relate to their own motor planning. In 28 healthy adults, we examined imitation and counter-imitation in a task that varied the likelihood of stimulus-response congruence from highly predictable, to moderately predictable, to unpredictable. To gain mechanistic insights into the statistical learning of stimulus-response compatibility, we compared two computational models of behaviour: (1) a classic fixed learning-rate model (Rescorla-Wagner reinforcement [RW]) and (2) a hierarchical model of perceptual-behavioural processes in which the learning rate adapts to the inferred environmental volatility (hierarchical Gaussian filter [HGF]). Though more complex and hence penalized by model selection, the HGF provided a more likely model of the participants' behaviour. Matching motor responses were only primed (faster) in the most experimentally volatile context. This bias was reversed so that mismatched actions were primed when beliefs about volatility were lower. Inferential statistics indicated that matching responses were only primed in unpredictable contexts when stimuli-response congruence was at 50:50 chance. Outside of these unpredictable blocks the classic stimulus-response compatibility effect was reversed: Incongruent responses were faster than congruent ones. We show that hierarchical Bayesian learning of environmental statistics may underlie response priming during dyadic interactions.

Visible skin disease symptoms of another person reduce automatic imitation of their hand movements.

Imitation is an important mechanism for social interaction and learning, and humans tend to imitate others automatically. While imitating others is often useful, it can backfire when imitation is incongruent with one's goals. For example, in forced-choice reaction time tasks, this tendency results in a reliable slowing of reactions if the observed and self-initiated actions are incompatible (compatibility effect). While imitation is commonly explained as a social phenomenon, previous results on the compatibility effect's dependence on social cues are inconsistent. However, in many previous studies, the associated social cues were easy to ignore by the participants. To make the social modifier more salient, the current study manipulated emotionally relevant aspects of the model hand itself in an imitation inhibition task by using models displaying skin disease symptoms which we expected to elicit (1) perceptions of dissimilarity and (2) disgust in participants. As predicted, participants' (n = 63) reaction times were influenced more by the incompatible actions of the symptom-free than the symptomatic model hand. However, both levels of self-reported disgust toward and self-other overlap with symptomatic hands were low and did not account for the observed effect on automatic imitation. Our findings show that automatic imitation depends on social factors if these are an integral part of the model and processed quickly, presumably due to their affective salience or the salience of the self-other distinction. Whether this effect is driven by emotional reactions to the model remains an open question.

Imitative and contagious behaviors in animals and their potential roles in the study of neurodevelopmental disorders.

Social learning in the forms of imitative and contagious behaviors are essential for learning abilities and social interaction. However, children with neurodevelopmental disorders and intellectual disabilities show impairments in these behaviors, which profoundly affect their communication skills and cognitive functions. Although these deficits are well studied in humans, pre-clinical animal model assessments of imitative and contagious behavioral deficits are limited. Here, we first define various forms of social learning as well as their developmental and evolutionary significance in humans. We also explore the impact of imitative and contagious behavioral deficits in several neurodevelopmental disorders associated with autistic-like symptoms. Second, we highlight imitative and contagious behaviors observed in nonhuman primates and other social animals commonly used as models for neurodevelopmental disorders. Lastly, we conceptualize these behaviors in the contexts of mirror neuron activity, learning, and empathy, which are highly debated topics. Taken together, this review furthers the understanding of imitative and contagious behaviors. We hope to prompt and guide future behavioral studies in animal models of neurodevelopmental disorders.

The mystery of emotional mimicry: multiple functions and processing levels in expression imitation.

Mimicry of appearance or of facial, vocal, or gestural expressions emerges frequently among members of different species. When such mimicry directly relates to affective aspects of an interaction, researchers talk about "emotional mimicry". Emotional mimicry has been amply documented but its functionality is still debated. Why and when do people mimic the expressions of others, who benefits, the mimicker or the mimicked, and how do they benefit? Which processes underlie emotional mimicry? Is it completely automatic and unconscious or can it be deliberate and conscious? The current Theory Section addresses these questions from different theoretical perspectives. The invited article by Hess and Fischer focused on the role of mimicry in social regulation and social bonding. The invited comment by Krets and Akyüz highlights information gathering and prediction in social interaction. The invited comment by Bernhold and Giles emphasizes vocal communication and its role in interpersonal accommodation. In this editorial, I propose the different theoretical perspectives may be integrated by assuming a multilevel appraisal and response generation mechanism. I also suggest that emotional mimicry research may be broadened by including social learning, vocal imitation, interspecies comparisons, and affective computing approaches.

Concurrently observed actions are represented not as compound actions but as independent actions.

Recent research suggests that we can simultaneously represent the actions of multiple agents in our motor system. However, it is unclear exactly how concurrently observed actions are represented. Here, we tested two competing hypotheses. According to the independence hypothesis, concurrently observed actions are represented as independent actions. According to the compound hypothesis, they are instead integrated, whenever possible, into compound actions. In Experiment 1 (N = 32), we first show that the standard imitation-inhibition task with a single hand can be extended to measure automatic imitation of compound actions. In Experiments 2-5 (NTotal = 368), we then investigated the representation of concurrently observed actions by further extending this task to include two hands. The results showed that two hands performing two different actions (e.g., one hand lifts index finger, one hand lifts middle finger) produced an effect similar to that of both hands performing just one of those actions (e.g., both hands lift index finger) but different from that of both hands performing both actions together (i.e., a compound action; lift both index and middle finger). This indicates that concurrently observed actions are coded as independent actions in the motor system. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Familiarity modulates both intra- and interspecific yawn contagion in red-capped mangabeys.

Yawn contagion (YC) is, compared to spontaneous yawning, an evolutionary recent phenomenon probably linked to behavioral synchronization in highly social species that is more likely when it involves familiar subjects. Here, we investigate for the first time in monkeys which factors modulate intra- and interspecific YC. Through an experimental approach, we exposed 17 red-capped mangabeys to video stimuli (Yawn vs Control) depicting familiar/unfamiliar red-capped mangabeys and humans, and unfamiliar hamadryas. We found that mangabeys yawned more often in response to Yawn than Control videos independently from the species depicted, demonstrating both intra- and interspecific YC in the tested species. Moreover, both mangabey and human familiar yawning stimuli evoked a stronger yawning response in the subjects compared to the unfamiliar counterparts. Neither the amount of time spent looking frontally at the screen (probability of stimulus perception) nor the levels of self-directed behaviors (a proxy of anxiety) accounted for the results. In conclusion, we provide the first evidence that in non-human primate familiarity modulates both intra- and inter-specific YC. Stimuli emitted by familiar faces somehow ease the mechanisms underlying YC, and this modulation can also apply to heterospecific subjects when previous shared experiences provide the prerequisites for the development of social bonds.