Background: Laughter is normally viewed as a spontaneous emotional expression of positive internal states; however, it more often serves as an intentional communicative tool, such as showing politeness, agreement and affiliation to others in daily interaction. Although laughter is a universal non-verbal vocalization that promotes social affiliation and maintains social bonds, its presence and usage is understudied in autism research. Limited research has focused on autistic children and found that they used laughter for expressing happiness and mirth, but rarely used it for social purposes compared to their neurotypical (NT) peers. To date, no research has included autistic adults. Objectives: The current study aims to investigate 1) the difference in laughter behaviour between pairs of one autistic and one neurotypical adult (MIXED dyads) and age-, gender- and IQ-matched pairs of two neurotypical adults (NT dyads); 2) whether the closeness of relationship (Friends/Strangers) would influence laughter production between MIXED and NT dyads. Method: In total, 27 autistic and 66 neurotypical adults were recruited and paired into 30 MIXED and 29 NT dyads in the Stranger condition and 7 MIXED dyads and 12 NT dyads in the Friend condition. (We were sadly only able to recruit 4 AUTISM dyads in the Stranger condition and 2 AUTISM dyads in the Friend condition, so these were not included in the analysis.) We filmed all dyads engaged in a funny conversational task and a video-watching task and their laughter behaviour was extracted, quantified and annotated. We calculated the Total duration of laughter, as well as the duration of all Shared laughter in each dyad. Results: Regardless of the closeness of relationship, MIXED dyads produced significantly less Total laughter than NT dyads in both the conversation task and video-watching task. The same tendency was also found for Shared laughter, although participants shared more laughter during video-watching than conversation and this tendency was more pronounced for NT than MIXED dyads. Strikingly, NT dyads produced more shared laughter when interacting with their friend than with a stranger during video-watching task, whilst the amount of shared laughter in MIXED dyads did not differ when interacting with their friend or a stranger. Conclusions: Autistic adults paired with neurotypical adults generally used laughter less as a communicative signal than neurotypical pairs during social interaction. Neurotypical adults pairs specifically produced more shared laughter when interacting with their friend than a stranger, whilst the amount of shared laughter produced by mixed pairs was not affected by the closeness of the relationship. This may indicate that autistic adults show a different pattern of laughter production relative to neurotypical adults during social communication. However, it is also possible that a mismatch between autistic and neurotypical communication, and specifically in existing friendships, may have resulted in patterns of laughter more akin to that seen between strangers. Future research will study shared laughter between pairs of autistic friends to distinguish between these possibilities.

Genuine and posed smiles are important social cues (Song, Over, & Carpenter, 2016). Autistic individuals struggle to reliably differentiate between them (Blampied, Johnston, Miles, & Liberty, 2010; Boraston, Corden, Miles, Skuse, & Blakemore, 2008), which may contribute to their difficulties in understanding others’ mental states. An intergroup bias has been found in non-autistic adults in identifying genuine from posed smiles (Young, 2017). This is the first study designed to investigate if autistic individuals would show a different pattern when differentiating smiles for in-groups and out-groups. Fifty-nine autistic adults were compared with forty non-autistic adults, matched on sex, age and nonverbal IQ. Roughly, half of each group were further randomly separated into two groups with a minimal group paradigm (adapted from Howard & Rothbart, 1980). There was no real difference between the groups, participants were primed to believe they were more similar to their in-groups. The ability to distinguish smiles was assessed on a 7-point Likert scale. We found both autism and non-autism groups rated genuine smiles more genuine than posed smiles and in-groups more genuine than out-groups. Even though both groups identified themselves more as in-group than out-group members, autistic individuals were less likely to than non-autistic individuals. However, autistic participants generally rated smiles as less genuine than non-autistic counterparts. These results indicate that autistic adults are capable of identifying genuine smiles from posed smiles, unlike previous findings; but they may be less convinced of the genuineness of others, which may affect their social communication thereafter. Importantly, autistic adults were equally influenced by social intergroup biases which has the potential to be used in interventions to alleviate their social difficulties in daily lives.