Electrophysiological Correlates of Subliminal Perception of Facial Expressions in Individuals with Autistic Traits: A Backward Masking Study

Abstract

People with Autism spectrum disorder (ASD) show difficulty in social communication, especially in the rapid assessment of emotion in faces. This study examined the processing of emotional faces in typically developing adults with high and low levels of autistic traits (measured using the Autism Spectrum Quotient-AQ). Event-related potentials (ERPs) were recorded during viewing of backward-masked neutral, fearful and happy faces presented under two conditions: subliminal (16 ms, below the level of visual conscious awareness) and supraliminal (166 ms, above the time required for visual conscious awareness). Individuals with low and high AQ differed in the processing of subliminal faces, with the low AQ group showing an enhanced N2 amplitude for subliminal happy faces. Some group differences were found in the condition effects, with the Low AQ showing shorter frontal P3b and N4 latencies for subliminal vs. supraliminal condition. Although results did not show any group differences on the face-specific N170 component, there were shorter N170 latencies for supraliminal vs. subliminal conditions across groups. The results observed on the N2, showing group differences in subliminal emotion processing, suggest that decreased sensitivity to the reward value of social stimuli is a common feature both of people with ASD as well as people with high autistic traits from the normal population.

Keywords: EEG; autism; backward masking; subconscious; subliminal facial emotions.

Figure 1

Experimental procedure.

Figure 2

A Pearson’s correlation between Autism Spectrum Quotient (AQ) and Empathy Quotient (EQ) scores. The results show a very strong, negative correlation between the AQ and EQ (r = −0.81, p < 0.0001).

Figure 3

Grand-average Event-related potential (ERP) waveforms of N2 amplitudes for Low AQ (A) and High AQ (B) groups (across all regions). The Low AQ group shows larger amplitudes for happy than neutral faces in the subliminal condition. The High AQ group does not show emotional differentiation.

Figure 4

Topographic maps for subliminal faces. Topographic maps show the cortical activities during 180–300 ms (N2) for subliminally presented fearful minus neutral and happy minus neutral faces in Low and High AQ groups. An increased negativity (blue color) is found for the Low AQ group for happy minus neutral faces predominantly in fronto-contral regions.

Figure 5

Grand-average ERP waveforms showing the N170 ERP for Low AQ (A) and High AQ (B) groups. There are larger amplitudes in the right hemisphere for both groups. However, the figures show reduced hemisphere lateralization in the High AQ.