Developmental Changes in Gaze Behaviour During Face Processing in Autism

Background: Autism is a neurodevelopmental disorder characterized by alterations in social interaction and emotional reciprocity which can be related to difficulties in understanding the mental states of others (“theory of mind”) and in processing efficiently facial information. Face perception depends on the integrity of several mechanisms, including an effective initial oculomotor exploration. Previous behavioral studies suggested an atypical visual scanning of faces in autism; subjects with autism disorder seem to explore the mouth area more than the eye area compared to control subjects. Most of these studies were based on an indirect evaluation of ocular behaviors, raising the problem of subjectivity. Since the last few years, the development of eye tracking systems provides access to an objective quantification of gaze behaviors grace to the precise measures of various ocular parameters (exploration and fixations time, pupil diameter).

Objectives: Using an eye tracking system, the current study aimed to provide a better understanding of the ocular behavior involved in face perception during typical and autistic development.

Methods: We quantified ocular behaviors of typical and autistic participants (children and adults), measuring the time of exploration and the time spent on the different areas of interest (eyes, nose and mouth) while exploring faces. A large population consisting of 52 healthy children (4-15 years), 44 healthy adults (18-35 years), 27 children with autism (4- 15 years) and 7 adults with autism (18-35 years) was included in this study.

Results: Our results showed that all subjects (controls and patients) spent significantly more time on the eye region than on the other areas of interest. However, subjects with autism spent significantly less time on the eye region than healthy subjects. Moreover, control subjects used a strategy based on their own eye dominance when exploring faces, beginning their exploration of a face by looking at the eye in the contra-lateral visual field to their own dominant eye. This strategy could not be found in patients with autism. Our developmental study also showed that the time spent on the area of the eyes increases significantly with age during typical development as well as in autistic development.

Conclusions: The preferred exploration of the eye region in control subjects suggests a focus of visual attention on this area, particularly rich in social information. The increase of the time spent on the eyes with increasing age could be related to the development of an exploration strategy linked to the face-expertise. Our data also showed that subjects with autism spent less time exploring the eyes compared to typical subjects. However, subjects with autism looked at the eyes significantly more than other facial areas of interest, this data contrasts with earlier reports of a lack of interest in the eye region in patients with autism. Moreover, this time spent on the eye region increases throughout autistic development, revealing an increasing interest for the eyes.