Increased Value of Biological Motion in Individuals with Few Autistic Traits

Background: Individuals with a diagnosis of Autism Spectrum Disorder (ASD) characteristically demonstrate impaired eye-contact during social interactions, and from an early age, look less towards faces than typically developing (TD) individuals. The Social Motivation Theory of Autism posits that this is due to a reduced sensitivity to the reward value of social stimuli, specifically faces, in ASD. Research has also demonstrated that TD individuals preferentially orient towards another type of salient social stimulus, namely biological motion. Individuals with ASD, however, do not show the aforementioned behaviours. Although the reward value of faces to TD and ASD individuals has been investigated, it remains unknown how rewarding both populations find biological motion.

Objectives: The present study investigated the value assigned to biological and non-biological motion by typically developing participants, and further examined whether reward values differed in individuals with more autistic traits. Videos of a human performing smooth, natural movements were used as a proxy for biological motion, and videos of a human performing rigid, robotic movements were used as a proxy for non-biological motion.

Methods: Autistic traits were measured in typically developing adults who then completed an innovative behavioural paradigm that measures stimuli preference.

Results: The results suggest that typically developing participants prefer biological, or human-like, motion, and exert more effort to view this type of stimuli in comparison to non-human-like motion or control stimuli. However, this preference appears to be weaker in individuals with more autistic traits.

Conclusions: This study is the first to investigate the reward value of biological motion in adult participants in the same way as has previously been investigated for faces. These results thus provide novel findings that TD individuals show a preference for biological motion, and that this preference is reduced in individuals with more autistic traits. Furthermore, this study helps us to begin to understand whether individuals with ASD assign a reduced reward value to faces alone, or whether these individuals find a broader conceptualisation of social stimuli less rewarding compared to TD individuals.