Individuals with ASD and their families frequently attribute the significant functional difficulties experienced to sensory symptoms. Sensory symptoms are reflected in behaviours such as hyper-reactivity (e.g. extreme distress in response to an unexpected sound), hypo-reactivity (e.g. failure to respond to a painful stimulus) and unusual sensory interests (e.g. excessive smelling of objects). These behaviours are observed in the absence of sensory loss (e.g. hearing impairment). Brain imaging supports differences in brain responses to sensory stimuli (e.g. heightened, attenuated, delayed or absent responses) in ASD when compared with non-ASD controls. Further, children with ASD are noted to experience altered autonomic nervous system (ANS) functions often linked with sensory symptoms, and emotional dysregulation and social impairments. Sensory symptoms are so common in ASD that they now form one subset of the diagnostic criteria for ASD. Therapies to remediate sensory symptoms are in high demand. In fact, occupational therapy, which is the lead profession providing sensory-directed therapies, is the second most frequently utilised therapy by families of children with ASD. The few controlled studies that examine the efficacy of sensory-directed therapies, however, report inconclusive results. A critical issue limiting previous research in this area is that sensory symptoms have been broadly defined and imprecisely characterised.
Our group has developed a method of classifying children with ASD into clinically meaningful subgroups based on their parent-reported sensory symptoms. We observe that children with ASD can be classified into four subtypes that vary on the dimensions of sensory reactivity (regulating the intensity of a response to a given stimulus) and multisensory integration (MSI; simultaneous processing of concurrent sensory modalities. Each sensory subtype has been found to display a distinct pattern of behaviour thus providing a novel basis on which to customise treatments. We propose that individuals with ASD vary in the extent to which they experience impairment in each sensory dimension and that this directly impacts their functional performance. Some individuals with ASD do not experience clinically significant differences on any sensory dimension (Adaptive), others display impairment on one dimension only (MSI or Reactive) and a further group exhibits difficulties on both dimensions (Generalised). We argue that this model forms the basis for the identification of clinically meaningful subgroups in ASD driven by sensory symptoms. The overall objective of our study is to begin to test this hypothesis by assessing the relative effectiveness of a sensory regulatory intervention for children with ASD classified as either Reactive or MSI. We predict that Reactive children will benefit more from the intervention than those in the MSI subtype."