Journal of Psychology and Psychiatry

ABSTRACT

The present cross-sectional observational study sought to examine disparities in the intensity and frequency of micro-emotional expressions — specifically Action Unit (AU)12 (smiling, index of social engagement) and AU45 (blinking, index of sensory sensitivity) between autistic and Neurotypical children during naturalistic, unstructured free-play interactions, highlighting an urgent gap in existing literature that predominantly relies on controlled clinical environments such as the Autism Diagnostic Observation Schedule (ADOS). Using convenient sampling methods, 18 age- and gender-matched children (8 autistic: mean age 8.4 years, SD = 2.7; 10 Neurotypical: mean age 8.2 years, SD = 2.5) were selected from a larger cohort study.

Open Face 2.0 along with the Facial Action Coding System (FACS) was used to computationally analyse ten-minute free-play video recordings to derive AU frequency (occurrences per session) and intensity (0–5 scale). No statistically significant variations between groups were detected using independent samples t-tests: AU12 intensity (autistic M = 0.55 ± 0.32, Neurotypical M = 0.75 ± 0.43; t(16) = 1.092, p = 0.291), AU12 frequency (autistic M = 267.8 ± 115.0, Neurotypical M = 302.8 ± 150.0; t(16) = −1.284, p = 0.217), and AU45 intensity (autistic M = 0.85 ± 0). Promising trends were indicated by moderate effect sizes (Cohen's d = −0.266 for AU12 frequency and d = −0.609 for AU45 frequency). AU12 and AU45 frequencies showed a significant positive connection across groups (r = 0.821, p < 0.01), indicating entwined social-sensory processing patterns. The results obtained indicate interpersonal variations in spontaneous emotional expressiveness in empirically relevant naturalistic situations could potentially be modest or extremely context-dependent, as opposed to consistently defined. Prospective studies ought to emphasize larger samples and multimodal approaches (e.g., physiological arousal metrics) to recognise complex behavioural trends and guide personalized, neurodiversity-affirming interventions for autistic children aiming at real-world interpersonal participation and sensory regulation without enforced Neurotypical norms of expressivity.

Keywords: Autism Spectrum Disorder (ASD); Emotional Expressions; Action Units (AU); Open Face 2.0; Facial Action Coding System (FACS); Naturalistic Observations; Neurotypical; Social Interactions