Virtual Reality System Overview

     While you may have heard of a Cave, our system would be better described as a "canvas". Our virtual environment supports precise correlation between haptic and visual feedback. By specializing, rather than generalizing, we've managed to optimize both precision and accuracy in measuring motor behavior during reaching and grasping motions, as well as perceptual judgments in a 3D space. Our system provides the most natural, precise form of haptic feedback available-- real-world physical objects. At the same time, it allows for full control over the viewable 3D visual stimulus. This provides very flexible experimental control of highly natural tasks.

     The flat-screen CRT monitor displays images at a resolution of 1152x860 pixels at a refresh rate of 118Hz. Thus, in conjunction with a pair of StereoGraphics Crystal Eyes active-stereo shutter glasses, we are capable of presenting a stereo image of the same resolution at 59 Hz. Our viewable workspace is approximately 40cm by 30cm at screen depth. Using 3dLabs Wildcat VP 970 video cards, we have acheived a minimal draw latency, meaning that on every draw cycle we are drawing with the most currently available tracking information.

     We use a two-way mirror to reflect the image from the monitor to the subject. In conjunction with the stereo glasses, this creates a virtual 3-dimensional workspace behind the mirror within which subjects can move their hands, manipulate objects, etc.. When a black screen is placed behind the mirror, subjects only see what is rendered on the display. The screen can be removed, however, to allow accurate 3D calibration of the different elements of the virtual environment and of the subjects' viewpoint.

     Our system depends upon knowledge of eye position to present the precise visual stimuli that we use. We do not currently use a head tracker to track free head movements; therefore, we use a chin rest which allows us to keep the head relatively still. A 52 point calibration routine run at the start of every experimental session gives us an excellent estimate of the left and right eye positions of the subject. The chin-rest is designed to to provide vibrational isolation between the subject and the visual stimulus by being mounted on seperate support structures. It is also designed to not impede the range of motion of the subject's shoulder. This allows for the most natural possible head-restrained reaching motions, without disturbing the visual stimuli.

     A Denso VS-E series robot arm provides precise six degree of positioning freedom. Six degrees of freedom combined with multiple custom head attachments allows for a broad range of haptic stimulus presentation. The robot is used for everything from aligning surfaces (for placement and pointing tasks) to custom shapes (for grasping tasks) all at precise positions and rotations.