Is implicit mentalising “social”? : Investigating the domain-specificity and developmental trajectory of implicit mentalising

Implicit mentalising involves the automatic awareness of others’ perspectives. While crucial to social functioning, its domain-specificity and developmental trajectory are debated. The Joint Simon task is thought to demonstrate implicit mentalising: Pairs sitting side-by-side perform a go/no-go task on the same screen, each responding to different coloured stimuli. Despite stimuli location being task-irrelevant, Joint participants respond faster to stimuli on their (vs. their partner’s) side; this is the Joint Simon Effect (JSE), which is stronger in a Joint versus Individual task condition. The JSE may stem from spontaneous co-representation of a partner’s frame-of-reference, creating a spatial overlap between stimulus-response location in the Joint (but not Individual) task. However, whether the JSE is driven by domain-specific social processes or domain-general processes remains debated. We investigated the potential contents of co-representation during task-sharing in adults (N=52)—typical geometric stimuli were replaced with two coloured sets of animal silhouettes, each assigned to either the participant or their partner. Critically, a surprise image recognition task followed to identify partner-driven effects in incidental memory exclusive to the Joint condition. Participants in the Joint task did not recognize their partner's stimuli more accurately than participants in the Individual task, implying that participants were no more likely to encode content from their partner’s perspective during the Joint task. However, Bayesian statistics (BF01=31.25) indicated a robust absence of the JSE, limiting interpretations of incidental memory findings, and raising questions regarding JSE’s replicability. To follow-up, we are investigating whether this pattern holds in children between 3.5- to 5-years-old (a critical period of explicit Theory of Mind development), after accounting for theoretically influential individual differences such as executive function, receptive vocabulary, and explicit ToM abilities. We will present the latest findings across adults and children, discussing the developmental trajectory of implicit mentalising, and the methodologies used to probe this question.