Mechanisms of top-down visual selection

Our visual world often contains many objects, only some of which are relevant to our behaviour. To survive in such an environment, we need to efficiently select the relevant information and to disregard stimuli that are irrelevant. The ability to direct attention to relevant information can be disrupted in a variety of neuropsychological disorders, including unilateral neglect. Since disorders such as neglect are indicators of poor recovery from a brain lesion, it is important to understand the factors that normally allow us to guide attention efficiently, and also to use this knowledge to guide the rehabilitation of such patients. We will conduct a programme of research to examine the functional and neural processes that allow us to direct attention in a ?top-down? manner, based on information held internally. To gain as full a picture as we can, we will use a variety of neuroscientific techniques including functional magnetic resonance imaging (fMRI), evoked potential responses (ERPs), trans-cranial magnetic stimulation (TMS) and neuropsychological studies of patients with discrete brain lesions, each of which can provide important pieces about neural function ? some providing information about the precise brain areas involved (fMRI), others about whether the brain regions are needed (TMS, lesion studies), and others about the temporal properties of the effects (ERPs). This work will assess how our expectancies of targets, how the action required by the task, and how information carried in working memory influences attention. We will finally examine whether cueing patients to attend across all the parts of objects can lead to functional recovery from neglect, providing proof of concept for rehabilitation studies.

Given that the visual world typically contains multiple objects, it is crucial for successful survival to be able to direct attention and action efficiently to those objects that are most relevant for our behaviour. The ability to direct attention can be affected in neuropsychological disorders such as unilateral neglect, and, in order to help such patients, it is important to understand the mechanisms that lead to the efficient guidance of attention to relevant stimuli. This work is concerned with understanding the mechanisms that determine the top-down guidance of attention, so that what we select is not driven slavishly on the basis of stimulus salience. We will examine how selection is influenced by: expectancies of targets, the task requirements including the action being performed, and the information carried in working memory. Converging evidence will be sought from a variety of cognitive neuroscientific procedures that will provide detailed information about the brain regions activated by the above factors (fMRI), whether these regions are necessary to performance (using trans-cranial magnetic stimulation and neuropsychological studies with patients), and the time parameters involved (evoked potential responses). The framework emerging from these studies will also be used to guide a remediation study where we will assess the effects on neglect patients of cueing attention to spread globally across objects, which may help to reduce object-based deficits of attention in such patients. We will evaluate whether this reduces neglect and has an impact on recovery of function.