Development of a Virtual Laboratory for the Study of Complex Human Behavior

The study of human perception has evolved from examining simple tasks executed in reduced laboratory conditions to the examination of complex, real-world behaviors. Virtual environments represent the next evolutionary step by allowing full stimulus control and repeatability for human subjects, and a testbed for evaluating models of human behavior. Visual resolution varies dramatically across the visual field, dropping orders of magnitude from central to peripheral vision. Humans move their gaze about a scene several times every second, projecting taskcritical areas of the scene onto the central retina. These eye movements are made even when the immediate task does not require high spatial resolution. Such “attentionally-driven” eye movements are important because they provide an externally observable marker of the way subjects deploy their attention while performing complex, real-world tasks. Tracking subjects’ eye movements while they perform complex tasks in virtual environments provides a window into perception. In addition to the ability to track subjects’ eyes in virtual environments, concurrent EEG recording provides a further indicator of cognitive state. We have developed a virtual reality laboratory in which head-mounted displays (HMDs) are instrumented with infrared video-based eyetrackers to monitor subjects’ eye movements while they perform a range of complex tasks such as driving, and manual tasks requiring careful eye-hand coordination. A go-kart mounted on a 6DOF motion platform provides kinesthetic feedback to subjects as they drive through a virtual town; a dual-haptic interface consisting of two SensAble Phantom extended range devices allows free motion and realistic force-feedback within a 1^3 m volume (Refer to PDF file for exact formulas)

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Is attention drawn to changes in familiar scenes?

In this study, we examined the mechanisms that control attention in natural scenes. We asked whether familiarity with the environment makes subjects more sensitive to changes or novel events in the scene. Previous investigation of this issue has been based on viewing 2-D images of simple objects or of natural scenes, a situation that does not accurately reflect the challenges of natural vision. We found that familiarity with the environment significantly increased the time spent fixating regions in the scene where a change had occurred. Together with previous work (Brockmole Henderson, 2005a, 2005b), our results support the hypothesis that we learn the structure of natural scenes over time, and that attention is attracted by deviations from the stored scene representation. Such a mechanism would allow deployment of attention to objects or events that were not explicitly on the current cognitive agenda

The role of exocentric reference frames in the perception of visual direction

One classic piece of evidence for an efference copy signal of eye position is that a small, positive afterimage viewed in darkness is perceived to move with the eye. When a small stationary reference point is visible the afterimage appears to move relative to the reference point. However, this is true only when the afterimage is localized to a small area. We have observed that when an extended afterimage of a complex scene is generated by a brief, bright flash it does not appear to move, even with large changes in eye position. When subjects were instructed to maintain their direction of gaze, we observed small saccades (typically < 1 deg) and slow drift movements often totalling more than 10 deg over a 30 sec period. When the instructions were to simply inspect the extended afterimage, subjects made larger saccades (up to 5 deg) which were not accompanied by afterimage movement. The smaller movements observed under the first instructions are greater than those observed in the dark or with small afterimages. When a visible reference is present with these large afterimages, the afterimage appears stationary, while the reference point appears to move. Eye position was monitored following the generation of such afterimages. In general, the perceived motion of the stationary reference point was in a direction opposite to the motion of the eye. Similar drift movements of smaller magnitude were observed with localized afterimages, but the motion was attributed to the afterimage