9222118 ROBERTSON A large body of research has demonstrated that spatial attentional scanning of the visual field can occur without accompanying eye movements. This is referred to as covert attentional orienting. Covert orienting allows one to search the visual field for information in a way that can confuse an observer as to one's actual focus of attention. Covert orienting also influences where one's eyes will move next. It is critical in gathering information to determine where visual resources are most needed, a process that has obvious survival value. Data from neurological patients have shown that covert orienting can break down in ways that affect only one half of space. More interestingly, the half that is affected is not limited to retinotopic coordinates or the visual field contralateral to the affected hemisphere. It also includes the half of space defined in scene-based coordinates. Right hemisphere damage will affect covert orienting into the left half of retinotopic space, but it also will affect covert orienting into the left half of a display rotated 90 degrees from upright where retinal and scene-based coordinates are dissociated. This fact means that at least some spatial parameters of the display are intact in these patients and are used to guide attentional search. It also suggests a very strong link between the internal representation of space and attentional search of the visual field. Experiments will address the question of how various spatial transformations of a display (rotation, reflection, and location translation) affect different types of attentional orienting. They will exploit a rightward bias in normals in early visual orienting to determine where search begins and what path it follows under various spatial transformations. Are some components of covert orienting tied to retinotopic space and others to scene-based space, and if so which ones operate in what space? The issue will be approached through the combine d study of normals and neurological patients who neglect one half of their visual space. These studies will lead to a fuller understanding of how the human brain represents a visual scene and the interaction between attentional mechanisms and the internal representations that are critical for action in the real world. ***
