Imagine walking into a crowded room, and all faces turn towards you. You might instantly recognize some familiar ones—an old friend, a colleague, or a family member. Others might be new, and specific details, like a pair of green eyes, or something in their overall appearance, may catch your attention. Later, you may remember some of the faces you encountered, while others remain more nebulous. This process, which most people are not even aware of, can significantly influence social interactions and building relationships, for better or for worse.

However, depending on your sex and neurotype, this face-processing can feel and play out very differently, with downstream effects on an individual's social connections and even mental health. Understanding the neural mechanisms behind these differences is key to better understanding individual experiences of social interactions and providing better support when needed. For example, women's performance in face processing has often been associated with an immediate initiation of face-processing in the brain, while autistic people's performance has been associated with delayed face-processing. However, is this reflected in the actual timing of the neural responses after seeing the image of a face?

This study focused on understanding the timing of neural responses to faces in a large cohort from the Longitudinal European Autism Project. We analysed EEG data from 492 participants, including both autistic and neurotypical individuals, across a wide age range (6-30 years). We used upright and inverted face photographs to trigger event-related potentials (ERPs) and investigated the timing and nature of sex and neurotype effects.

Timing of Neural Responses

We found that the influence of sex on neural responses occurred earlier (around 260 ms post-stimulus) than the influence of neurotype (around 310 ms post-stimulus), while both persisted into the later stages of processing. Of note, both effects emerged relatively late after the initiation of face processing in the brain (after 250 ms), suggesting an influence of sex and neurotype in deferred cognitive processes rather than immediate perceptual processing as previously assumed.

Age and Developmental Trajectories

In this time window associated with deferred cognitive processes, female children exhibited stronger neural responses to face inversion (a measure of face-processing specialization) than their male counterparts. This enhanced response in females diminished during adolescence and was not significant in adulthood, indicating that maturation leads to a convergence of face-processing capabilities across sexes.

Sex and Neurotype Interaction

Autistic females showed a delayed and reduced neural response to face inversion compared to neurotypical females, a difference that lessened with age and became non-significant by adulthood. In contrast, no significant age-dependent differences were observed in males, suggesting sex-specific developmental trajectories in face processing among autistic individuals.

Implications for Understanding Autism

By identifying the timing and nature of a specific neural response, this work contributes to the understanding of the neurocognitive profiles of autistic individuals, emphasizing the need to consider sex and age. Furthermore, it highlights that sex differences in face processing are more pronounced in childhood and suggests that females, both neurotypical and autistic, allocate more neural resources to face processing when they are young. The diminishing differences with age imply that socialization and cognitive development contribute to a homogenization of face-processing abilities, potentially offering insights into how support can be tailored across different ages.

The study employed two methods that go beyond traditional ERP analyses: (a) Bootstrapped Cluster-based Permutation Analysis (BCPA) – allowing high temporal resolution in detecting the timing of differing neural responses – and Growth Curve Analysis (GCA) – that helped us understand the developmental trajectory and interaction effects across different age groups.

As research progresses, integrating concurrent measures like EEG, eye-tracking, and behavioural assessments will be crucial in translating these insights into real-life accommodations. Understanding these basic neural mechanisms opens new avenues for understanding the social and cognitive development of autistic individuals.