Preference for biological motion is reduced in ASD: implications for clinical trials and the search for biomarkers
Authors: Mason L. , Shic F. , Falck-Ytter T. , Chakrabarti B. , Charman T. , Loth E. , Tillmann J. , Banaschewski T. , Baron-Cohen S. , Bölte S. , Buitelaar J. , Durston S. , Oranje B. , Persico A. M. , Beckmann C. , Bougeron T. , Dell’Acqua F. , Ecker C. , Moessnang C. , Murphy D. , Johnson M. H. , Jones E. J. H. ,   the LEAP Team*, Ahmad Jumana , Ambrosino Sara , Baumeister Sarah , Bours Carsten , Brammer Michael , Brandeis Daniel , Brogna Claudia , de Bruijn Yvette , Chatham Chris , Cornelissen Ineke , Crawley Daisy , Dumas Guillaume , Faulkner Jessica , Frouin Vincent , Garcés Pilar , Goyard David , Ham Lindsay , Hipp Joerg , Holt Rosemary , Lai Meng-Chuan , D’ardhuy Xavier Liogier , Lombardo Michael V. , Lythgoe David J. , Mandl René , Marquand Andre , Mennes Maarten , Meyer-Lindenberg Andreas , Bast Nico , Oakley Bethany , O’Dwyer Laurence , Oldehinkel Marianne , Pandina Gahan , Ruggeri Barbara , Ruigrok Amber , Sabet Jessica , Sacco Roberto , Cáceres Antonia San José , Simonoff Emily , Spooren Will , Toro Roberto , Tost Heike , Waldman Jack , Williams Steve C. R. , Wooldridge Caroline , Zwiers Marcel P. 
Published: December 2021

Abstract
Background
The neurocognitive mechanisms underlying autism spectrum disorder (ASD) remain unclear. Progress has been largely hampered by small sample sizes, variable age ranges and resulting inconsistent findings. There is a pressing need for large definitive studies to delineate the nature and extent of key case/control differences to direct research towards fruitful areas for future investigation. Here we focus on perception of biological motion, a promising index of social brain function which may be altered in ASD. In a large sample ranging from childhood to adulthood, we assess whether biological motion preference differs in ASD compared to neurotypical participants (NT), how differences are modulated by age and sex and whether they are associated with dimensional variation in concurrent or later symptomatology.

Methods
Eye-tracking data were collected from 486 6-to-30-year-old autistic (N = 282) and non-autistic control (N = 204) participants whilst they viewed 28 trials pairing biological (BM) and control (non-biological, CTRL) motion. Preference for the biological motion stimulus was calculated as (1) proportion looking time difference (BM-CTRL) and (2) peak look duration difference (BM-CTRL).

Results
The ASD group showed a present but weaker preference for biological motion than the NT group. The nature of the control stimulus modulated preference for biological motion in both groups. Biological motion preference did not vary with age, gender, or concurrent or prospective social communicative skill within the ASD group, although a lack of clear preference for either stimulus was associated with higher social-communicative symptoms at baseline.

Limitations
The paired visual preference we used may underestimate preference for a stimulus in younger and lower IQ individuals. Our ASD group had a lower average IQ by approximately seven points. 18% of our sample was not analysed for various technical and behavioural reasons.

Conclusions
Biological motion preference elicits small-to-medium-sized case–control effects, but individual differences do not strongly relate to core social autism associated symptomatology. We interpret this as an autistic difference (as opposed to a deficit) likely manifest in social brain regions. The extent to which this is an innate difference present from birth and central to the autistic phenotype, or the consequence of a life lived with ASD, is unclear.