Sensory Processing Differences, Mental Health and Mood in Autistic Adults

Autism spectrum disorder (hereafter ‘autism’) is a lifelong neurodevelopmental condition, characterised by persistent differences in social communication and interaction, and restricted, repetitive patterns of behaviours (DSM 5, DSM 5-TR; American Psychiatric Association, 2013; American Psychiatric Association, 2022). Autistic people face high rates of co-occurring mental health challenges across the lifespan, leading to substantial long-term negative impacts on their quality of life (Lai et al., 2019). The current thesis generates novel insights into an autism-specific putative risk factor for various mental health outcomes, namely sensory processing differences (SPDs), which are characterised as the differences in how sensory stimuli are perceived, processed, appraised, and responded to across all sensory modalities (He et al., 2023). SPDs in autism have been investigated for decades (Ben-Sasson et al., 2019) and were more recently identified as one of the top ten research priorities within the autism community. Nevertheless, important knowledge gaps persist in this field. First, despite SPDs being pervasively present in adulthood (Weiland et al., 2020), current sensory research has primarily focused on younger autistic groups. Second, existing sensory research has largely relied on traditional one-off sensory assessments, assuming that sensory processing reflects a relatively stable set of traits (Manning et al., 2025). However, SPDs can fluctuate within an individual depending on personal (e.g., moods) and environmental (e.g., social contexts) factors (Dunn, 1997; MacLennan et al., 2022). Therefore, the dynamic and context-dependent nature of SPDs in autistic people’s everyday lives remain underexplored. This thesis employs a mixed-methods approach to advance current understanding of SPDs in autistic people. The first chapter provides a general overview of the background of SPDs in autism research. Chapter 2, a systematic review and meta-analysis, provides evidence on the relationships between SPDs and internalising / externalising problems among autistic people. Longitudinal studies (e.g., Green et al., 2012) also demonstrated a predictive relationship, suggesting that SPDs may represent a potential risk factor for later mental health issues. Given the underrepresentation of older autistic adults in this field, Chapter 3 presents a study to further current knowledge of SPDs and the role in mental health across midlife and older autistic adulthood. The second half of the thesis focuses on the implementation of ecological momentary assessment (EMA) with autistic populations. Chapter 4, a systematic review, examines the feasibility and applicability of EMA in autism research. Chapters 5 and 6 describe an EMA study of SPDs, examining the feasibility of using EMA to capture daily sensory experiences among autistic adults (Chapter 5) and exploring momentary SPDs and their relationships with mood states (Chapter 6). The final chapter (Chapter 7) provides an overarching discussion of the findings and implications of the thesis with consideration to future direction, strengths, and limitations.