Distance Perception & Perceptual-Motor Adaptation


Our research on distance estimation and perceptual adaptation in real and virtual environments is designed to better understand how people perceive virtual environments. We are especially interested in examining why people underestimate distance in different kinds of virtual environments and how experience in a virtual environment affects perception of the size and distance of objects.


Dynamic Affordances in Embodied Interactive Systems: The Role of Display and Mode of Locomotion

Many practical applications of VR technology rely on adequate immersive representations of 3D spaces and support of embodied, dynamic interactions with the virtual world. Evaluation of these properties remains an important research problem. This project aimed at developing a method of conducting user evaluations of dynamic, full-body interactions in VR systems based on using support for perception and action coupling as a criterion for comparison.

We investigated how the properties of interactive virtual reality systems affect user behavior in full-body embodied interations. Our experiment compared four interactive virtual reality systems using different display types (CAVE vs. HMD) and modes of locomotion (walking vs. joystick). Participants performed a perceptual-motor coordination task, in which they had to choose among a series of opportunities to pass through a gate that cycled open and closed and then board a moving train. Mode of locomotion, but not type of display, affected how participants chose opportunities for action. Both mode of locomotion and display affected performance when participants acted on their choices. We concluded that technological properties of a virtual reality system (both display and mode of locomotion) significantly affected opportunities for action available in the environment (affordances) which has strong implications for design and practical applications of immersive interactive systems. 

Flexible Recalibration of Perception and Action in Children and Adults

As we locomote through the world, we constantly experience the relationship between our rate of physical movement and the rate of visual motion. For example, if we walk quickly down a sidewalk, we experience a faster rate of visual motion than if we walk slowly. Over time, this vast experience with the relationship between perception and action allows the system to build up expectations about how a given amount of movement will lead to a given amount of distance traveled. The regularity between the rate of movement and the distance traveled is altered only through mechanical devices such as moving sidewalks in airports. In such cases, a given rate of walking produces a greater amount of distance traveled than we normally experience. With enough experience on a moving sidewalk, people should recalibrate, or adapt to a new relationship between perception and action.

We conducted eight experiments to examine how manipulating perception vs. action during walking affects perception-action recalibration in real and imagined blindfolded walking tasks. Participants first performed a distance estimation task (pretest), and then walked through an immersive virtual environment on a treadmill for 10 minutes. Participants then repeated the distance estimation task (posttest), the results of which were compared to their pretest performance. In Experiments 1a, 2a, and 3a, participants walked at a normal speed during recalibration, but the rate of visual motion was either twice as fast or half as fast as the participants' walking speed. In Experiments 1b and 2b, we tested 12-year-old children in the same recalibration task as 1a and 2a. In Experiments 1c, 2c, and 3b, the rate of visual motion was kept constant, but participants walked at either a faster or a slower speed. During pre- and posttest, we used either a blindfolded walking distance estimation task or an imagined walking distance estimation task.

Additionally, participants performed the pretest and posttest distance estimation tasks in either the real environment or in the virtual environment. With blindfolded walking as the distance estimation task for pre- and posttest, we found a recalibration effect when either the rate of visual motion or the walking speed was manipulated during the recalibration phase. With imagined walking as the distance estimation task, we found a recalibration effect when the rate of visual motion was manipulated but not when the walking speed was manipulated in both the real environment and the virtual environment. Neither blindfolded walking nor imagined walking yielded significant results when 12-year-old children were tested. 

Adapting to Scale Changes in Virtual Environments

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A large body of work examining distance estimation in virtual environments has shown that distances are underestimated in virtual environments, especially when the environment is viewed through a head mounted display (HMD) system, A related question that has received far less attention is how does calibrating space perception in one virtual environment affect space perception in another virtual environment? We addressed this question by examining whether experience with making distance estimates in a virtual environment of one scale affects people’s perception of the same distances in an identical virtual environment of a different scale.

In each of four experiments, participants first gained experience making distance estimates in a tunnel-like virtual environment with feedback (adaptation) and then made additional distance estimates in an identical, but differently scaled virtual environment without feedback (test). The same distances were used in adaptation and test. We examined three types of scale changes: 1) changing the size of the tunnel, 2) changing the size of the targets, and 3) changing the separation of the targets. In the first two experiments, we compared the effect of scaling only the tunnel with the effect of simultaneously scaling everything (i.e., the tunnel, targets, and target separation). We used joystick movement in the first experiment and blindfolded walking in the second experiment to determine whether the same effects on distance estimation were observed with different types of locomotion. In addition, we examined whether the direction of the scale change affected distance estimates by carrying out adaption in a small tunnel and test in a large tunnel, and vice versa. In the third experiment, we examined how changing both the size of the targets and the separation between the targets affected distance estimates via blindfolded walking. In the final experiment, we examined how changing either the size of the targets or the separation between the targets affected distance estimates via blindfolded walking.

We found that changes in target size always affected distance estimates at test. When the targets became smaller, participants overshot distance and when the targets became larger, participants undershot distance. Changes in the size of the tunnel or the separation between the targets (without a change in the size of the targets) had a minimal effect on distance estimates. These results indicate that distance estimates at test were strongly influenced by familiar size cues for distance. However, participants' adjustments of their distance estimates were only a small proportion of the 3.3 factor by which object size was increased or decreased from adaptation to test. Further work is needed to better understand how people integrate information from multiple distance cues in the face of scale changes.