Individual Face Discrimination and the Influence of Fixation in ASD Measured with Fpvs EEG

Background:

Fluently recognizing faces and facial expressions is highly important for our social interactions. Impaired and atypical face processing have often been postulated as a key deficit in autism spectrum disorders (ASD). Furthermore, decreased visual attention to the eye region has been suggested in ASD, as well as an increased preference for the mouth region of faces. Despite the great amount of research on face identity and facial expression recognition in ASD, results are mixed.

Objectives:

Therefore, we wish to examine face processing in ASD by means of an implicit and innovative EEG approach, and we will relate EEG findings to visual face scanning patterns assessed with eye-tracking.

Methods:

We combine fast periodic visual stimulation (FPVS) with scalp electroencephalography (EEG) and eye-tracking. The core idea of FPVS is that the periodicity of the electrophysiological response on the human scalp corresponds exactly with the periodicity (frequency) of the visual stimulation. Hence, it can be used for efficiently measuring categorization responses of complex visual stimuli in the human brain.

First, the ability to rapidly discriminate individual faces was assessed in matched groups of boys with (N = 23) and without (N=23) ASD. If oddball images of various facial identities are periodically interleaved in a series of identical faces, the sensitivity to facial identity can be quantified by assessing the neural response at this oddball frequency. Additionally, we manipulated the orientation of the faces (upright versus inverted), as well as the position of the fixation cross (the eye region versus the mouth region).

In a second paradigm, administered in the same groups, we examined spontaneous visual face processing both with frequency-tagging EEG (preferential neural processing) and with eye-tracking (preferential looking) . In this paradigm, the eye and the mouth region of a face are each flickering at a particular frequency, which allows to disentangle the neural processing of the eye versus mouth region. The neural responses to each of the face parts were quantified and were related to the simultaneous eye-tracking data.

Results: We observed a significantly lower neural sensitivity for individual face discrimination in the ASD group, as indicated by lower bilateral occipito-temporal responses. This group difference was present no matter whether the fixation was on the eye region or on the mouth region, but is specific for upright and not for inverted faces. At the conference we will also add and discuss the results of the second paradigm, investigating preferential neural processing and preferential looking of the eye region versus the mouth region of faces.

Conclusions:

The literature suggests that individuals with ASD show face processing impairments and atypical visual scanning patterns. We examined these hypotheses with an innovative EEG paradigm. We found impaired holistic processing of faces in the ASD group, not modulated by the position of the fixation cross. Additionally, we examined how spontaneous visual face processing patterns differ in children with ASD versus typically developing children, by measuring both which face part (eye or mouth region) is preferentially processed (EEG) and which part is preferentially looked at (eye-tracking).