Vision

The area of visual space perception continues to benefit from the use of immersive virtual environment technology. One important reason is that, in comparison with more conventional 3-D computer graphics displayed on desktop CRTs, an immersive virtual display, even one employing an HMD, can provide the user with the perceptual experience of being inside a large-scale environment (e.g., a large room, a building, an outdoor setting). This means that the researcher can investigate the perception of distance, size, and motion at larger scales not permitted by conventional CRTs and yet have the convenience of computer-based research. Our group is currently using virtual environment technology for several research projects, including: 1) measuring visually perceived distance, 2) examining how perceptual motor transforms are learned, and 3) understanding the perception of lightness and shape.

Current Projects:

Perception of Egocentric Distance in Virtual Environments

Over the last several years, Josh Knapp and Jack Loomis have been conducting research on how well people perceive egocentric distance in virtual environments, using methods developed by Jack and his colleagues for real environments (Fukusima, Loomis, and DaSilva, 1997; Loomis, DaSilva, Fujita, & Fukusima, 1992; Loomis, Klatzky, Philbeck, & Golledge, 1998; Philbeck & Loomis, 1997; Philbeck, Loomis, & Beall, 1997). In contrast to full-cue viewing in real environments where distance perception is accurate out to 15 or 20 m, full-cue viewing in computer-simulated virtual environments results in consistent underestimation of distance (a factor of about ½) for the same range of distances (Knapp, 1999; Loomis & Knapp, in press). Research by Josh, Jack, and Andy Beall will use photorealistic virtual environments to determine if distance perception is more accurate.

Microgravity Visual/Vestibular Experiments

Though we don't think about it much, the force of gravity profoundly effects human experience as we go about our daily lives here on Earth. In contrast to birds and aquatic animals, most of the large turning movements humans make are in a gravitationally horizontal plane. We are used to seeing most objects from our normal upright head orientation. But the experience of living in weightlessness is quite different for humans. Your life is not fettered to a single plane. You can move in any direction, and work upside down if you want to. Astronauts on previous flights have reported that when working upside down, they frequently experience striking visual illusions as to what seems "up" and "down", and say they have difficulty recognizing familiar objects in unfamiliar orientations. When these illusions happen, they seem to trigger space sickness. The specific goal of experiments conducted by Andy Beall is to quantify and model these problems, and see whether they persist on long duration flights. We're trying to reverse-engineer the mind, and figure out the rules it uses to combine sensory cues. We know people differ in terms of how much weight they give to visual cues relative to inner ear cues in judging the vertical here on Earth. Can we predict whether they will have problems when they fly in space ? Do astronauts eventually develop a more robust orientation ability ? Or does the human evolutionary heritage and our lifetime of mono-oriented experience with our environment constrain what we can learn to do ? Knowing the answers to these questions will help us figure out what kinds of preflight training and spacecraft interior architectures will reduce disorientation and space sickness. Inevitably we'll also better understand the role vision can play in spatial orientation here on Earth, both in normal individuals, and in patients with inner ear disease.

This is an example of one of the virtual environments we used for the experiments. This image is generated in realtime and in stereo and seen by the astronauts while wearing the head-mounted display (see picture below).

Crew member Jay Buckey performing an experiment using the NASA virtual environment generator during STS-95 (April 1999)

Here's a stereo-pair (crossed fusion) of a scene from our experiment.

Optic Flow

In the spirit of other optic flow research, we address the problem of how a pilot turns an airplane into alignment with a runway, a maneuver that is one of the more challenging phases of visually controlled flight. In earlier work, Loomis and Beall (1992) proposed a rule for turning an aircraft into alignment: Turn the aircraft in such a way as to hold constant the rate of change of splay (the angle the projected runway makes with respect to the vertical). The experiment shown below was a psychophysical test of this rule. We compared day and night landing approaches as our experimental manipulation; we were interested in any role that ground texture might play in the spatial judgement involved in performing the landing approach. Three pilots varying in flight experience performed multiple approaches in a light aircraft for a total of 26 day and 25 night approaches. The three-dimensional trajectories of the aircraft were measured using differential global position system data. From these trajectories we computed a variety of motion variables (e.g., turn rate) and two optic flow variables (splay and splay rate). The similar performance of day and night approaches suggests that the pilots were using optic flow variables that were invariant with changes in the visibility of ground texture. A computer model was developed based on the optic flow rule and estimates of human visual processing thresholds. We conclude that the model gives a good description of pilot performance as test in our experiment and may help to illuminate the cause of a class of airplane accidents during the common landing phase.