Differences in the Late Positive Potential ERP As a Function of Valence Versus Intensity in Adults with and without ASD

Background:  Research suggests that individuals with Autism Spectrum Disorder (ASD) demonstrate aberrant neural processing of emotionally salient social stimuli (Lerner et al., 2013). Research has focused on early stage face processing as indexed by the N170 and VPP event-related potentials (ERP) recorded via electroencephalogram (EEG; Bentin et al. , 1996; Faja, et al. 2016) showing blunted processing of emotional faces in individuals with ASD (McPartland et al., 2011). While these findings have been well-replicated, ERP research focusing on the later stages of emotional face processing in ASD has been largely neglected. The late positive potential (LPP), a slow wave ERP beginning 300ms after stimulus onset, is associated with sustained attention and motivation and larger amplitudes are found in response to salient emotional stimuli in typically developing (TD) individuals (Hajcak et al., 2009). One study has examined the LPP in individuals with ASD, finding an enhanced LPP to nonsocial vs. positive social stimuli (Benning et al., 2016). However, this study did not (1) control for differences in amplitude of early facial processing, which may evince differences that prefigure the LPP, and (2) identify whether LPP differences in the ASD group were a function of stimulus valence or intensity. It is essential to parse apart the stimulus qualities that contribute to LPP differences to better understand social emotional processing deficits.

Objectives:  This study examined differential LPP response to high vs. low intensity and positively vs. negatively valenced emotional in individuals with and without ASD while controlling for differences in amplitude of early stage processing.

Methods:  Thirty-two TD adults (10 male; M_age=22, SD_age=6.0), and 13 IQ-matched adults with ADOS-2 confirmed ASD diagnosis (11 male; M_age=27, SD_age=6.8) completed an ERP measure of facial emotion recognition (DANVA-2; Nowicki, 2004). VPP and LPP to high and low intensity, and positively and negatively valenced, emotional faces were extracted from ERP data. We examined the interaction between stimulus type (high vs. low or positive vs. negative) and diagnosis for LPP via repeated measures ANOVAs while covarying VPP amplitude.

Results:  There was a significant interaction between intensity level and diagnosis (F=5.35, p<.05) such that individuals with ASD had a smaller LPP amplitude to high intensity faces (B = .28, p<.05; Figure 1). This interaction was robust to controlling for VPP amplitude to high intensity faces (F=5.62, p<.05). There was no effect for LPP for valence by condition.

Conclusions:  While their slow wave neural responses to emotional valence appear to be intact, individuals with ASD demonstrate attenuated motivated attention to high intensity social emotional stimuli compared to their TD peers even when controlling for amplitude differences in early processing (i.e. VPP). Although previous research has focused on early ERP differences in processing low intensity emotions which may reflect blunted initial sensory processing, the current findings highlight attenuated later stage processing of high intensity faces, suggesting diminished motivational response to highly salient social information in the ASD group relative to TD controls. This study suggests that deficits in processing social emotional information vary across stages of processing in individuals with ASD.