Glasgow Psychosis Screening tool for use in adults with Intellectual Disabilities (GPS-ID): development and psychometric properties

Background: Prevalence of psychosis is known to be higher in adults with intellectual disabilities (ID) than in the general adult population. However, there have been no attempts to develop a psychosis screening tool specifically for the adult ID population. The present study describes the development and preliminary evaluation of a new measure, the Glasgow Psychosis Screening tool for use in Adults with Intellectual Disabilities (GPS-ID). Method: An item pool was generated following: 1) focus groups with adults with ID and psychosis, and their carers and/or workers; 2) expert input from clinicians. A draft scale was compiled and refined following expert feedback. The new scale, along with the Psychotic Symptom Rating Scales was administered to 20 adults with ID (10 with and 10 without psychosis) and their relative or carers. Results: The GPS-ID total score, self-report subscale and informant rating-subscale differentiated psychosis and non-psychosis groups. The tool had good internal consistency (Cronbach’s α=0.91), and a cut-off score ≥4 yielded high sensitivity (90%) and specificity (100%). The method of tool development supports face and content validity. Criterion validity was not supported. Conclusions: Preliminary investigation of the tool’s psychometric properties is positive, although further investigation is required. The tool is accessible to adults with mild to moderate ID and can be completed in 15-30 minutes. The GPS-ID is not a diagnostic tool, therefore any adult exceeding the cut-off score of ≥4 should receive further assessment.

Mapping and modulating spatial attention asymmetries in young and older adults

Healthy young adults demonstrate a group-level, systematic preference for stimuli presented in the left side of space relative to the right (‘pseudoneglect’) (Bowers & Heilman, 1980). This results in an overestimation of features such as size, brightness, numerosity and spatial frequency in the left hemispace, probably as a result of right cerebral hemisphere dominance for visuospatial attention. This spatial attention asymmetry is reduced in the healthy older population, and can be shifted entirely into right hemispace under certain conditions. Although this rightward shift has been consistently documented in behavioural experiments, there is very little neuroimaging evidence to explain this effect at a neuroanatomical level. In this thesis, I used behavioural methodology and electroencephalography (EEG) to map spatial attention asymmetries in young and older adults. I then use transcranial direct current stimulation (tDCS) to modulate these spatial biases, with the aim of assessing age-related differences in response to tDCS. In the first of three experiments presented in this thesis, I report in Chapter Two that five different spatial attention tasks provide consistent intra-task measures of spatial bias in young adults across two testing days. There were, however, no inter-task correlations between the five tasks, indicating that pseudoneglect is at least partially driven by task-dependent patterns of neural activity. In Chapter Three, anodal tDCS was applied separately to the left (P5) and right (P6) posterior parietal cortex (PPC) in young and older adults, with an aim to improve the detection of stimuli appearing in the contralateral visual field. There were no age differences in response to tDCS, but there were significant differences depending on baseline performance. Relative to a sham tDCS protocol, tDCS applied to the right PPC resulted in maintained visual detection across both visual fields in adults who were good at the task at baseline. In contrast, left PPC tDCS resulted in reduced detection sensitivity across both visual fields in poor performers. Finally, in Chapter Four, I report a right-hemisphere lateralisation of EEG activity in young adults that was present for long (but not short) landmark task lines. In contrast, older adults demonstrated no lateralised activity for either line length, thus providing novel evidence of an age-related reduction of hemispheric asymmetry in older adults. The results of this thesis provide evidence of a highly complex set of factors that underlie spatial attention asymmetries in healthy young and older adults.