Increased Inter-Trial Variability in Sensory Processing of Social Stimuli in Children and Adolescents with ASD
In Autism Spectrum Disorder (ASD) neural correlates of sensory processing differ from matched typically developed controls (TDC). Most studies have focused on differences in group means but have not compared intra-individual variability of neural processing. The model of reduced sensory precision posits that sensory processing abnormalities in ASD may be caused by increased variability in the neural response patterns to sensory information (see Baum et al., 2015 for an overview). First studies have already indicated increased variability in neural markers of sensory processing (Dinstein et al., 2012; Haigh et al., 2014; Milne, 2011).
The objective of the current study was to test the hypothesis of reduced sensory precision during the processing of social stimuli. For this purpose the variability of a neural marker of sensory processing, namely the P100, was compared between children and adolescents with ASD and TDC. Furthermore, the correlation of this variability with performance in social perception tasks was explored.
In a sample of 21 children and adolescents with ASD and 15 age, IQ and gender matched TDC EEG was recorded during the viewing of emotional facial expressions. EEG data were analysed on the single trial level, identifying P100 amplitude and latency for 60 trials. The median absolute deviation (MAD), which reflects the degree of variability across trials (Milne, 2011), as well as mean amplitude were computed for each participant. Mean and MAD were compared across groups using univariate ANOVA.
No between-group difference for mean P100 amplitude was found (F(1,34)=.450 p=.507). In contrast, MAD of the P100 amplitude was increased in ASD compared to TDC (F(1,34)=4.616 p=.039). Higher variability in P100 amplitude correlated with poorer performance (r(36)=-.387 p=.010) as well as increased reaction times (r(36)=.351 p=.018) in an emotion discrimination task.
Results confirm increased variability in sensory processing of emotional facial expressions in children and adolescents with ASD. Importantly, the analysis of inter-trial variability seems to provide information on neural processing differences between ASD and TDC which do not become evident by a comparison of mean amplitudes. Furthermore increased variability is linked to deficits in facial emotion processing. These findings indicate that reduced sensory precision indeed contributes to social perception deficits in ASD. Further replication is needed to confirm this hypothesis. Preliminary analyses of P100 variability during biological motion processing indicate similar patterns also apply to other areas of social perception.