Time Course of Facial Emotion Recognition in First-Degree Relatives of Individuals with ASD: An Eye-Tracking Study

Background: Previous studies have found impaired facial emotion recognition and atypical gaze fixation patterns when looking at faces in participants with Autism Spectrum Disorders (ASD) (Klin et al, 2002). Specifically, participants with ASD look more at the mouth and less at the eyes, while typically developing participants show an opposite pattern. Several studies found the same pattern in unaffected siblings and parents of children with ASD, suggesting that it may be a feature of Broad Autism Phenotype (BAP) (Adolphs et al, 2008). However, this finding has not always been replicated; furthermore, it was proposed that other traits, such as alexithymia, can better explain the atypical eye:mouth ratio found in ASD (Bird et al, 2011).

Objectives:   Little is known about the time course of gaze fixation on faces in relation to ASD symptoms. Preference for looking at the eyes or the mouth could be a consequence of automatic tendency to immediately fixate on the eyes, in which case the difference would be seen early on, or be a part of a conscious strategy. Averaging total fixation duration over a given interval of time (which was commonly done in previous studies) does not allow to disambiguate between these two factors. Our aim was to investigate the time course of facial emotion processing in first-degree relatives of individuals with ASD.

Methods:  We employed the visual world paradigm: At the beginning of each trial participants heard a word indicating a target emotion, and at the same time saw photos of four different people presented in the four quadrants of the screen. The task was to respond whether one among the four photos expressed the target emotion.  The outcome variable was the probability of fixation within a given region of interest at each time point.

Results: Preliminary data from 7 parents of children with ASD and 15 control participants indicate that participants from both groups start to look towards the target emotion  around 150-200 ms after trial onset. However, the probability of fixation on target emotion increased at significantly slower rate in the BAP group (compared to control). With respect to eye:mouth ratio, both participant groups initially looked more at the mouth, but later switched towards looking at the eyes. In the typical group, probability of fixation on the mouth continued to increase, albeit at a slower rate, while the BAP group fixated mainly on the eyes (Group (BAP, Control) *Region (Eyes, Mouth) * Time (300, 500, 700 ms) interaction, F(2,40)=5.61, p=.021).

Conclusions:  Eye:mouth ratio is task-dependent, and it follows a particular time course. Contrary to previous findings, the BAP group did not avoid looking at the eyes, arguing against lower eye:mouth ratio being an endophenotypic feature of ASD. However, the BAP group focused exclusively at the eyes, while the typical group explored all facial features in parallel, suggesting that just like people with a clinical diagnosis of ASD, their first-degree relatives analyze facial expressions based on single feature.