Assessing Asymmetries in the Distribution of Attention across the Whole Visual Field in Unilateral Spatial Neglect

Unilateral spatial neglect (USN) is defined as the impaired or lost ability to respond to sensory stimuli (auditory, visual, tactile and olfactory) presented in the contralesional hemispace of a neurological patient. USN is caused by lesions, typically strokes, that can occur in both the left and right hemisphere of the brain, but with lesions in the right hemisphere typically causing the more severe and persistent deficits. 

USN is one of the single best predictors of poor functional recovery following stroke and despite the clinical significance of the condition, the underlying cognitive deficits are not well understood. In the absence of a biological marker for unilateral neglect, clinicians are reliant on paper and pencil tests (e.g. line bisection, cancellation tasks) that have limited diagnostic sensitivity and suffer from a number of methodological problems.
The hypothesis of this study was that a prototypical random dot motion (RDM) direction discrimination task can be objectively used to accurately diagnose the presence and severity of USN in stroke patients. The main objective of this study was to obtain behavioural and electrophysiological data from a cohort of right hemisphere stroke patients and healthy control subjects using the RDM task, and compare the results to the gold standard paper & pen tests currently used to clinically assess unilateral spatial neglect. The main objective was achieved and the primary results indicated that the RDM could be used to objectively diagnose the presence of USN through the measure of detection accuracy. The measure of reaction time to targets was deemed unreliable due to a low number of valid trials. However, a relatively new decision signal, known as the centroparietal positive potential (CPP), was successfully evoked in the control group, indicating that the RDM task was capable of eliciting the required brain signals needed to objectively measure neglect. A future objective is to increase task compliance, primarily through decreasing the difficulty of the task, which should increase the number of valid trials available for analysis and thus pave the way for validating an objective measure for tracking the severity of USN.