James F. Cremer

How does presentation method and measurement protocol affect distance estimation in real and virtual environments

We conducted two experiments that compared distance perception in real and virtual environments in six visual presentation methods using either timed imagined walking or direct blindfolded walking, while controlling for several other factors that could potentially impact distance perception. Our presentation conditions included unencumbered real world, real world seen through an HMD, virtual world seen through an HMD, augmented reality seen through an HMD, virtual world seen on multiple, large immersive screens, and photo-based presentation of the real world seen on multiple, large immersive screens. We found that there was a similar degree of underestimation of distance in the HMD and large-screen presentations of virtual environments. We also found that while wearing the HMD can cause some degree of distance underestimation, this effect depends on the measurement protocol used. Finally, we found that photo-based presentation did not help to improve distance perception in a large-screen immersive display system. The discussion focuses on points of similarity and difference with previous work on distance estimation in real and virtual environments.

HCSM: a framework for behavior and scenario control in virtual environments

This paper presents HCSM, a framework for behavior and scenario control based on communicating hierarchical, concurrent state machines. We specify the structure and an operational execution model of HCSMs state machines. Without providing formal semantics, we provide enough detail to implement the state machines and an execution engine to run them. HCSM explicitly marries the reactive (or logical) portion of system behavior with the control activities that produce the behavior. HCSM state machines contain activity functions that produce outputs each time a machine is executed. An activity functions output value is computed as a function of accessible external data and the outputs of lower-level state machines. We show how this enables HCSM to model behaviors that involve attending to multiple concurrent concerns and arbitrating between conflicting demands for limited resources. The execution algorithm is free of order dependencies that cause robustness and stability problems in behavior modeling. In addition, we examine the problems of populating virtual environments with autonomous agents exhibiting interesting behavior and of authoring scenarios involving such agents. We argue that HCSM is well suited for modeling the reactive behavior of autonomous agents and for directing such agents to produce desired situations. We demonstrate use of HCSM for modeling vehicle behavior and orchestrating scenarios in the Iowa Driving Simulator, an immersive real-time virtual driving environment.

Children's Road Crossing A Window Into Perceptual–Motor Development

Most research on perceptual–motor development has focused on changes occurring during infancy and toddlerhood. In this paper, we describe our work on the development of perceptual–motor development during late childhood and early adolescence in the context of an important applied problem: bicycling across traffic-filled roads. Specifically, we have examined the gaps between cars that children and adults accept when bicycling across intersections, using an immersive, interactive bicycling simulator. This work highlights both methodological advances in using immersive, interactive virtual environments to study perceptual–motor functioning as well as theoretical advances in understanding the problem of moving the self in relation to other moving objects. We conclude with ideas for future research and practical implications of this work.

Driving simulation: challenges for VR technology

Virtual driving environments represent a challenging test for virtual reality technology. We present an overview of our work on the problems of scenario and scene modeling for virtual environments (VEs) in the context of the Iowa Driving Simulator (IDS). The requirements of driving simulation-a deterministic real-time software system that integrates components for user interaction, simulation, and scenario and scene modeling-make it a valuable proving ground for VE technologies. The goal of our research is not simply to improve driving simulation, but to develop technology that benefits a wide variety of VE applications. For example, our work on authoring high-fidelity VE databases and on directable scenarios populated with believable agents also targets applications involving interaction with simulated, walking humans and training in the operation of complex machinery. This work has benefited greatly from the experience of developing components for a full-scale operational VE system like IDS, and we believe that many other proposed VE technologies would similarly benefit from such real-world testing.

Estimating Distance in Real and Virtual Environments: Does Order Make a Difference?

In this investigation, we examined how the order in which people experience real and virtual environments influences their distance estimates. Participants made two sets of distance estimates in one of the following conditions: (1) real environment first, virtual environment second; (2) virtual environment first, real environment second; (3) real environment first, real environment second; or (4) virtual environment first, virtual environment second. In Experiment 1, the participants imagined how long it would take to walk to targets in real and virtual environments. The participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), the participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, the participants’ second estimates did not differ significantly across the two environments. A second experiment, in which the participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment, replicated these results. These subtle yet persistent order effects suggest that memory can play an important role in distance perception.

Formulating Three-Dimensional Contact Dynamics Problems

ABSTRACT Complementarity formulations are a promising approach for solving dynamic multi-rigid-body contact problems. Two aspects of simulating contact in a complementarity setting are addressed here. First, an explicit formulation of the differential equations governing contact points for bodies of general surface geometry is developed. These equations may be used to integrate the contact position and to set up the basic dynamics equations. Second, an efficient method for handling frictionless planar contacts of arbitrary boundary shape is presented. Throughout, the problem is set up as explicitly as possible, with special attention being given to the way that the contact geometry is related to the dynamics.

Steering behaviors for autonomous vehicles in virtual environments

This paper presents steering behaviors that control autonomous vehicles populating roadways in virtual urban environments. Behavior programming is facilitated by a set of representations of the environment that use convenient frames of reference in natural coordinate systems. Roadway surfaces are modeled as three-dimensional ribbons that make the local orientation of the road explicit and allow relative distances on the road to be simply computed. Roads and intersections are connected to form a ribbon network. An egocentric representation called a path melds road and intersection segments into a single, continuous ribbon that captures the vehicles short-term plan of navigation. A topological structure called a route supports wayfinding. We describe how the interrelated ribbon, path, and route representations are used to build multi-component behaviors that plan routes and safely navigate through traffic filled road networks - tracking lanes, shifting lanes to avoid congestion, anticipating lane changes needed to make turns dictated by the route, negotiating intersections, and respecting the rules of the road.

Hierarchical, concurrent state machines for behavior modeling and scenario control

This paper presents a framework for behavior modeling and scenario control based on hierarchical, concurrent state machines (HCSM). We present the structure and informal operational semantics of hierarchical, concurrent state machines. We describe the use of HCSM for scenario control in the Iowa Driving Simulator (IDS), a virtual environment for real-time driving simulation. The paper concludes with an outline of a forthcoming HCSM-based scenario authoring system that will permit non-specialists to graphically program behaviors and design experiments for IDS.<<ETX>>

Perceiving and acting on complex affordances: how children and adults bicycle across two lanes of opposing traffic

This investigation examined how children and adults negotiate a challenging perceptual-motor problem with significant real-world implications--bicycling across two lanes of opposing traffic. Twelve- and 14-year-olds and adults rode a bicycling simulator through an immersive virtual environment. Participants crossed intersections with continuous cross traffic coming from opposing directions. Opportunities for crossing were divided into aligned (far gap opens with or before near gap) and rolling (far gap opens after near gap) gap pairs. Children and adults preferred rolling to aligned gap pairs, though this preference was stronger for adults than for children. Crossing aligned versus rolling gap pairs produced substantial differences in direction of travel, speed of crossing, and timing of entry into the near and far lanes. For both aligned and rolling gap pairs, children demonstrated less skill than adults in coordinating self and object movement. These findings have implications for understanding perception-action-cognition links and for understanding risk factors underlying car-bicycle collisions.

The architecture of Newton, a general-purpose dynamics simulator

The architecture of Newton, a general-purpose system for simulating the dynamics of complex physical objects, is described. The system automatically formulates and analyzes equations of motion, and performs automatic modification of this system of equations when necessitated by changes in kinematic relationships between objects. Impact and temporary contact are handled, although only using simple models. User-directed influence of simulations is achieved using Newtons module, which can be used to experiment with the control of many-degree-of-freedom articulated objects.<<ETX>>