The Nature and Influence of Sensory Processing Deficits in Developmental Coordination Disorder

"This thesis presents the case of Developmental Coordination Disorder (DCD), a common yet understudied neurodevelopmental disorder in which the primary symptoms are motor difficulties. Previous research has reported several cognitive and perceptual difficulties, that may underly the primary motor difficulty of DCD. However, characterisation of the cognitive abilities of individuals with DCD has not always been consistent. For example, in the case of inhibition, group differences seem to be largely task specific, with individuals with DCD achieving comparable performance on verbal inhibition tasks, but tend to be slower and make more errors on non-verbal measures of inhibition. However, slower information processing, as consistently observed in the disorder, may mean that poorer performance on nonverbal inhibition tasks in DCD may not be due to an inhibitory deficit itself, but may instead be explained by poorer information, and perceptual processing.After an introduction to DCD, and the known aetiology of the disorder in Chapter 1, Chapter 2 describes the methodology used to ascertain the presence of DCD within the studies presented within this thesis. Chapter 3 will investigate the integrity of non-verbal motor inhibition in adults with and without DCD. Throughout the thesis, adults with possible DCD (pDCD) are included within a secondary analysis of an expanded DCD+pDCD group. Chapter 3 will utilise a Choice Reaction Task (CRT) to quantify reaction times to differential stimuli in adults with DCD. This will be followed by the employment of a Stop Signal Task (SST), designed to allow for a measurement of the time taken to inhibit a response, independent of the time required to perceive and respond to a stimulus. Bayesian inference of SST data will further allow for the delineation of parameters relating to response initiation, on Go trials, and stopping errors, on Stop trials.In Chapter 4, adults with DCD and pDCD are compared to neurotypical (NT) adults on a broad range of perceptual psychophysical tasks. Assessed domains include haptic detection and discrimination, spatio-temporal, and audio-visual integration. While previous studies have identified perceptual difficulties in DCD in isolated modalities, this represents the first to use a wide range of psychophysical measurements within the same sample of participants. Chapters 5 and 6 represent attempts to identify neural markers of perceptual dysfunction in DCD, in the context of the internal modelling deficit hypothesis, in order to assess the relationship of these neural markers to sensory processing, and the building of internal movement models. A general discussion will then be presented in Chapter 7, of the findings across all chapters, to identify the key results of the thesis as a whole, and what this means for an understanding of DCD.