Visual and physiological mechanisms underlying emotion processing in autism and alexithymia

Impairments in emotion processing are one of the key diagnostic social symptoms of autism. Proposed explanatory mechanisms include atypical visual perceptual processes (e.g., social attention) and physiological responses to socioemotional stimuli (e.g., other people’s faces). However, experimental evidence for these processes has been highly equivocal, and prevailing models have been unable to account for the documented individual differences observed in these processes. Chapter 1 reviews the current conceptualisation of autism and outlines the theoretical context of my research, highlighting key hypotheses and mechanisms underlying emotion processing in autism which will be explored throughout the thesis. In particular, the potential explanatory role of the “alexithymia hypothesis” is discussed. Alexithymia is a condition frequently co-occurring with (but not unique to) autism and is linked to individual differences in socioemotional processes that have been implicated in autism (e.g., social attention, emotion processing, physiological responses). This thesis will therefore investigate the contribution of alexithymia to several aspects of socioemotional functioning thought to be linked to autism. Chapter 2 investigated the spatiotemporal dynamics of gaze allocation to faces during emotion processing tasks in autism and alexithymia, and contrasted traditional social attention hypotheses to recent applications of Bayesian accounts of autism to social attention processes. Evidence from traditional and novel methods revealed that atypical eye gaze during emotion processing is best predicted by alexithymia in both autistic and non-autistic individuals. Specifically, alexithymia affected the non-linear temporal patterns of gaze allocation to faces and predicted reduced modulation of eye gaze to cued visual exploration of emotions. The alexithymia effect is argued to reflect imprecise emotion concepts and priors for spatiotemporal dynamics of facial expressions. This proposal was supported by three additional experiments in Chapter 3 linking alexithymia to atypical modulation of social attention and emotion processing by stimulus dynamics, and by task- and emotion- relevant priors. Chapter 4 focused on exploring the potential role of alexithymia in disrupting links between physiological responding and emotion processing proposed by arousal-based models of autism and alexithymia. A novel approach capitalising on multimodal recording of physiological responses, was used to characterise multivariate profiles of physiological mobilisation to emotions. This approach provided evidence for alexithymia, not autism, driven effects on atypical physiological mobilisation to emotions, and puts forth a novel hypothesis with implications for autonomic and interoceptive accounts of alexithymia, autism and emotion. One remaining challenge to the alexithymia hypothesis has been the possibility that alexithymia may simply reflect expected variation within the already multifaceted autism phenotype. In Chapter 5, two large-scale studies of clinical and non-clinical samples used confirmatory factor analysis and network psychometric modelling to address this remaining question. Results suggested separate underlying latent factors for alexithymia and autism, as well as separate clusters of symptoms which highlighted structural and dimensional distinctions of the two conditions. In Chapter 6, I discuss the implications of this body of work for theory and practice and outline novel directions for research on autism, alexithymia and socioemotional processes. Combined, this body of work provides the most extensive test of the alexithymia hypothesis and highlights the specific mechanisms through which alexithymia affects socio-emotional processes in autism. This work also offers a model for studying typical and atypical socioemotional processes and several methodological and conceptual advances with implications for basic and applied research on socioemotional processes.