Autistic and non-autistic people use their faces to express emotions in systematically different ways, according to new research from the University of Birmingham. The findings could help explain why emotional signals are frequently misunderstood between autistic and non-autistic individuals.
Researchers created one of the most detailed libraries of emotional facial movements to date using advanced motion-tracking technology. Their findings, published in Autism Research, suggest that both the appearance and timing of facial expressions differ between the two groups.
How researchers mapped expressions
The team studied 25 autistic adults and 26 non-autistic adults, capturing nearly 5,000 deliberate facial expressions. Participants were asked to express anger, happiness and sadness in two different scenarios: while matching facial expressions to sounds and while speaking.
Facial motion capture generated more than 265 million data points, allowing researchers to analyze tiny movements in the muscles around the eyes, mouth and eyebrows. This level of detail revealed consistent group-level patterns rather than simply random differences between individuals.
Key emotional differences found
When expressing anger, autistic participants relied more heavily on mouth movements and showed less pronounced eyebrow activity compared with non-autistic participants. Their expressions also developed differently over time, adding another distinction to how anger appeared on the face.
When expressing happiness, autistic adults tended to show a subtler smile that was less visible around the eyes. Their expressions of sadness often involved a stronger lift of the upper lip to create a downturned appearance, differing from the more typical combination of mouth and eyebrow movements.
Role of alexithymia in emotion
The researchers also investigated alexithymia, a trait involving difficulty identifying and describing one’s own emotions that is more common among autistic people. Participants with higher levels of alexithymia displayed less clearly defined expressions of anger and happiness.
These less distinct expressions made it more difficult for observers to categorize the emotion, potentially contributing to ambiguity during social interactions. The findings suggest that alexithymia may influence how easily facial expressions can be interpreted, regardless of whether someone is autistic.
A two-way communication challenge
Lead author Dr Connor Keating said the findings show that autistic and non-autistic people differ not only in what their facial expressions look like but also in how smoothly those expressions unfold over time. This may help explain mutual difficulties in interpreting one another’s emotional states.
Senior author Professor Jennifer Cook stressed that these patterns should not be viewed as deficits in autistic people. Instead, she compared the differences to speaking distinct but equally meaningful emotional “languages,” framing misunderstandings as a two-way communication challenge rather than a one-sided impairment.
The findings add support to the “double empathy” theory, which proposes that misunderstandings between autistic and non-autistic people can arise from mismatched communication styles on both sides. The researchers are now exploring whether tailored training could improve emotional understanding between the two groups.
The project was funded by the UK Medical Research Council and the European Union’s Horizon 2020 programme, reflecting growing international interest in more nuanced and socially grounded approaches to autism research.
