Attention and perceived stability across eye movements

The purpose of this research is to investigate the role of attention in maintaining spatial continuity across eye movements. The eyes move several times each second, and with each eye movement, the entire visual array moves across the retina. When driving, for instance, we may shift our direction of gaze from the rearview mirror to the gear shift, causing the entire windscreen to shift from the lower visual field to the upper visual field. Yet we do not seem to lose track of the visual scene as a whole, and in particular we seem to have little difficulty maintaining the focus of our attention on the locations where important information (such as oncoming traffic) will appear. Indeed, the shift across the retina of the entire visual scene has surprisingly little impact on our subjective sense of space and continuity, despite the fact that when the eyes move, all the neurons in visual cortex suddenly begin receiving information from a new location in space. Visual mechanisms must exist that assist us in maintaining accurate representations of relative space over changes in their retinal positions. One candidate is known as saccadic remapping: namely, cells in some visual cortex regions have been demonstrated to respond to the visual array as though it were already in the retinal locations that it will be in when the impending eye movement is completed. The source of this signal seems to be, at least in part, the eye movement system itself. Saccadic remapping has been suggested to underlie our subjective sense of continuity by providing a continuous representation of visual space over eye movements, though not much is known about how much it actually contributes to visual experience in human observers. This project will investigate the nature of spatial stability over eye movements, specifically assessing whether selective visual attention is a fundamental component of the process. Specific questions that will be addressed are: to what extent do eye movements disrupt spatial attention to peripheral locations? To what extent does attending to specific objects in the environment determine whether their spatial information will be preserved across an eye movement? To what extent do we rely on stable environmental information to keep track of objects when they move on our retina? Behavioural research on healthy observers and patients with brain damage will be used to address these questions. The answers will shed light on the fundamental mechanisms underlying the continuity of conscious visual experience.