Backchannels in conversations between autistic adults are less frequent and less diverse prosodically and lexically

Abstract Backchannels (BCs; listener signals such as ‘mmhm’ or ‘okay’) are a ubiquitous and essential feature of spoken interaction. They are used by listeners predominantly to support the ongoing turn of their interlocutor and to signal understanding and agreement. Listeners seem to be highly sensitive to the exact realisations of BCs and to judge deviations from typical forms as negative. Very little is known about the use of BCs by speakers diagnosed with autism spectrum disorder (ASD). In dialogue recordings of 28 German adults in two groups of disposition-matched dyads (i.e., both interlocutors were either autistic or non-autistic), we found that the ASD group was characterised by (1) a lower rate of BCs per minute (particularly in the early stages of conversation), (2) less diversity in the lexical realisation of BCs and (3) a less diverse and flexible mapping of different intonation contours to different BC types. We interpret these results as reflecting more general characteristics of autistic as compared to non-autistic individuals, namely different strategies in signalling attention towards an interlocutor and less flexible behaviour in social interaction.