Sensory Processing in ADHD and ASD: From Superficially Similar Profiles to Divergent Underlying Structures

This thesis investigates whether attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) share a common neural substrate, using sensory processing as a tool to interrogate this question. Across three empirical studies integrating both self-reports, clinical diagnosis and psychophysical assessment, and employing network analysis, mediation modelling, correlational analysis and analysis of covariance (ANCOVA), the project examines the similar or divergent nature of ADHD and ASD by looking at how they interact with each other and with sensory processing, and the impact comorbid conditions have on these interactions. The findings indicate that sensory processing is not an intrinsic feature of ADHD or ASD, but rather a relatively autonomous domain. Intermediary conditions, such as anxiety impact, mediate or modulate, the connection between ADHD and ASD and sensory processing through their underlying interaction with the core conditions’ traits. These interactions do not have the same impact across ADHD and ASD- where anxiety may affect ADHD traits in their interaction with sensory processing in a certain manner, it may not necessarily do so for ASD. Differences were observed also across clinical and trait-based cohorts, indicating that ADHD behaviour aligned better with dimensional models, while ASD aligned better with hybrid or categorical models, once more elucidating different rather than similar profiles. Critically, superficially similar sensory phenomena in ADHD and ASD did not arise from a shared underlying mechanism. Comparable behavioural outcomes emerged through distinct interactions between early perceptual processes and regulatory dynamics, demonstrating equifinality at the behavioural level alongside divergence at the mechanistic level. Furthermore, this thesis confirms that sensory processing can be used as a beneficial tool to investigate common and divergent basis into ADHD and ASD.