Brain mechanisms of social signalling in live social interactions with autistic and neurotypical adults.

The simple act of watching another person can change a person's behaviour in subtle but important ways; the individual being watched is now capable of signalling to the watcher, and may use this opportunity to communicate to the watcher. Recent data shows that people will spontaneously imitate more when being watched. Here, we examine the neural and cognitive mechanisms of being watched during spontaneous social imitation in autistic and neurotypical adults using fNIRS brain imaging. Participants (n = 44) took part in a block-moving task where they were instructed only to copy the block sequence which people normally do using a straight low action trajectory. Here, the demonstrator sometimes used an atypical 'high' action trajectory, giving participants the opportunity to spontaneously copy the high trajectory even if this slowed their performance. The confederate who demonstrated each block sequence could watch the participant's actions or close her eyes, giving a factorial design with factors of trajectory (high/low) and watched (watched/unwatched). Throughout the task, brain signals were captured from bilateral temporal/parietal/occipital cortex using fNIRS. We found that all participants performed higher actions when being watched by the confederate than when not being watched, with no differences between autistic and neurotypical participants. The unwatched conditions were associated with higher activity of the right inferior parietal lobule in all participants and also engagement of left STS only in autistic participants. These findings are consistent with the claim that people engage different neural mechanisms when watched and unwatched and that participants with autism may engage additional brain mechanisms to match neurotypical behaviour and compensate for social difficulties. However, further studies will be needed to replicate these results in a larger sample of participants.

Social signalling as a framework for second-person neuroscience.

Despite the recent increase in second-person neuroscience research, it is still hard to understand which neurocognitive mechanisms underlie real-time social behaviours. Here, we propose that social signalling can help us understand social interactions both at the single- and two-brain level in terms of social signal exchanges between senders and receivers. First, we show how subtle manipulations of being watched provide an important tool to dissect meaningful social signals. We then focus on how social signalling can help us build testable hypotheses for second-person neuroscience with the example of imitation and gaze behaviour. Finally, we suggest that linking neural activity to specific social signals will be key to fully understand the neurocognitive systems engaged during face-to-face interactions.

Adults imitate to send a social signal.

Humans frequently imitate each other's actions with high fidelity, and different reasons have been proposed for why they do so. Here we test the hypothesis that imitation can act as a social signal, with imitation occurring with greater fidelity when a participant is being watched. In a preregistered study, 30 pairs of naïve participants played an augmented-reality game involving moving blocks in space. We compared imitation fidelity between trials where the leader watched the followers' action, and trials where the leader did not watch. Followers imitated the trajectory height demonstrated by the leader, and critically, the strength of this correlation was greater in trials where the follower knew the leader was watching them. This suggests that followers spontaneously used imitation as a social signal in a nonverbal interaction task, supporting socio-communicative hypotheses of imitation.

How can the study of action kinematics inform our understanding of human social interaction?

The kinematics of human actions are influenced by the social context in which they are performed. Motion-capture technology has allowed researchers to build up a detailed and complex picture of how action kinematics vary across different social contexts. Here we review three task domains-point-to-point imitation tasks, motor interference tasks and reach-to-grasp tasks-to critically evaluate how these tasks can inform our understanding of social interactions. First, we consider how actions within these task domains are performed in a non-social context, before highlighting how a plethora of social cues can perturb the baseline kinematics. We show that there is considerable overlap in the findings from these different tasks domains but also highlight the inconsistencies in the literature and the possible reasons for this. Specifically, we draw attention to the pitfalls of dealing with rich, kinematic data. As a way to avoid these pitfalls, we call for greater standardisation and clarity in the reporting of kinematic measures and suggest the field would benefit from a move towards more naturalistic tasks.