Beyond the Social Motor Synchrony model: neurodivergent children and familiar partners can synchronise movements through tailored tasks and contexts

Some theorists argue that autistic people have a deficit in Interpersonal Synchrony, accounting for the social differences central to diagnostic criteria (e.g., Fitzpatrick et al., 2016). Evidence suggests synchrony is lower in interactions between an autistic partner and a non-autistic partner, compared with two non-autistic partners (e.g., McNaughton & Redcay, 2020). However, few studies examine synchrony in autistic pairs, and autistic people describe communication and interaction with other autistic partners as more comfortable and attuned than interactions with non-autistic partners (Crompton, Hallett et al., 2020). This thesis examines Social Motor Synchrony (SMS) in autistic people and autistic and non-autistic interaction partners across three studies. SMS refers to the way two or more people rhythmically match their non-verbal and non-facial body movements during social interaction (Bernieri & Rosenthal, 1991). It is an element of social relationships that supports smooth exchanges and feelings of connectedness.

SMS is a property of a relationship, and both partners are required to mutually engage and adapt their behaviours to facilitate synchrony (Laursen & Hartup, 2002; Markova et al., 1995). However, SMS is sometimes implicitly treated as an individual characteristic, meaning that potential differences in SMS between matched- or mixed-neurotype partnerships, and the broader context of the interaction, have been missed. Emerging theories suggest an interpersonal mismatch occurs between autistic and non-autistic people, which may result in lower synchrony (Bolis et al., 2018; Milton, 2012), and might explain greater feelings of connectedness in matched- compared with mixed-neurotype interactions (Crompton, Hallett et al., 2020). In this thesis, I adopt an interpersonal framework to study SMS in autistic people and their interaction partners.

In the first study, I systematically review the literature examining SMS in autism. Most studies found lower SMS in mixed-neurotype pairs (i.e., an autistic and a non-autistic partner) compared with two non-autistic partners, which is characterised as showing an SMS deficit in the autistic partner (e.g., McNaughton & Redcay, 2020). However, I identified only three papers involving two autistic partners. The dearth of research involving autistic peers is an important gap given the potential for attuned social relationships between autistic people (Sasson et al., 2017). With this review, I also identified the possible effect of the tasks and environmental contexts used so far on the SMS displayed by autistic people and their partners.

The review findings informed the tasks and social context of the second and third studies. I used Motion Energy Analysis, a novel automated method to detect micro-level motor synchrony, to examine SMS in Study 2: between familiar partners of the same neurotype (i.e., autistic pairs and non-autistic pairs of children), and Study 3: between young neurodivergent adults (learners) and their Learning Support Workers (LSWs). In both studies, partners played collaborative activities on tablet devices, personalised to the interests of the autistic children and learners. Both studies revealed synchrony at levels higher than chance. Study 2 also indicated that autistic pairs can synchronise to a similar, and possibly greater, degree than pairs of non-autistic partners under certain conditions.

In study 3, Intensive Interaction (II) was used with the learners throughout their curriculum at a special education college. II is a learner-led approach, where the practitioner follows the movements and vocalisations of the learner. The approach involves joining in with the learners' movements to create synchronous interactions and responding to their behaviours to create non-verbal communicative exchanges (Hewett et al., 2011). II has been observed to support improvements in reciprocal non-verbal communication between neurodivergent learners and LSWs (Zeedyk et al., 2009). Some research also indicates that autistic people might be less likely than non-autistic people to adapt their movements to a partner’s movements to facilitate synchrony, which might support the idea of a synchrony deficit in the autistic partner. I therefore examined the balance of synchrony over time by measuring which partner most frequently acted as the leader, and therefore which the follower. Learners and LSWs led the synchronous interactions to an equal degree. This demonstrates that mixed-neurotype pairs can display balanced and reciprocal interactions, and that neurodivergent learners can adapt their movements to a partner’s movements to an equal degree as a non-autistic person can. I discuss the potential for Intensive Interaction to support attunement in mixed-neurotype interactions.

This thesis represents a move away from the study of social behaviour in autism at an individual level to the level of the interaction. The results contribute to our theoretical understanding of SMS in autism by challenging the notion of a synchrony trait deficit. Amendments are therefore needed to an SMS model of autism, which suggests SMS challenges underpin the social differences in autism. These studies are among the first to examine SMS in comfortable social and environmental contexts and using tasks that are tailored to the needs and interests of autistic participants. I demonstrate the potential for Motion Energy Analysis to observe patterns of close synchrony in these settings and with autistic people who are frequently excluded from research due to profound difficulties with verbal communication. The pattern of close synchrony demonstrates the potential impact of the context on synchronous interaction. The close synchrony observed in these scenarios helps develop our understanding of SMS in autistic people and their partners, which may vary according to the context. This thesis therefore underscores the importance of examining social interaction differences in autism from an interpersonal framework with consideration for the situatedness of the autistic person.