Artifacts in an environment afford to their observers utility and function directly through specific object characteristics (e.g., mediums, surfaces, substances). Virtual environments (VEs) similarly seek to afford specific utility to their users, whether it is for training, education, or entertainment, thus it seems natural to consider basing VE designs on affordances. Such affordance-based design should yield significant benefits by providing designs that behave in more understandable and intuitive manners. These designs should be easier to learn, adapt better to user tasks, and frustrate users less by allowing use of the same skills acquired via real-world interactions. In order to realize affordance-based VE designs, the types of appropriate affordances and means of realizing these affordances must be identified. Currently, however, affordances lack a theoretical and operational basis for such application. The present paper suggests functions that affordances should support and provides a conceptual model for realizing affordances based on sensory-stimuli-substitution schemes.

Visually induced motion sickness, or “cybersickness”, has been well documented in all kinds of vehicular simulators and in many virtual environments. It probably occurs in all virtual environments. Cybersickness has many known determinants, including (a short list) field-of-view, flicker, transport delays, duration of exposure, gender, and susceptibility to motion sickness. Since many of these determinants can be controlled, a major objective in designing virtual environments is to hold cybersickness below a specified level a specified proportion of the time. More than 20 years ago C. W. Simon presented a research strategy based on fractional factorial experiments that was capable in principle of realizing this objective. With one notable exception, however, this strategy was not adopted by the human factors community. The main reason was that implementing Simon's strategy was a major undertaking, very time-consuming, and very costly. In addition, many investigators were not satisfied that Simon had adequately addressed issues of statistical reliability. The present paper proposes a modified Simonian approach to the same objective (holding cybersickness below specified standards) with some loss in the range of application but a greatly reduced commitment of resources.

Although simulator sickness is known to increase with protracted exposure and to diminish with repeated sessions, limited systematic research has been performed in these areas. This study reviewed the few studies with sufficient information available to determine the effect that exposure duration and repeated exposure have on motion sickness. This evaluation confirmed that longer exposures produce more symptoms and that total sickness subsides over repeated exposures. Additional evaluation was performed to investigate the precise form of this relationship and to determine whether the same form was generalizable across varied simulator environments. The results indicated that exposure duration and repeated exposures are significantly linearly related to sickness outcomes (duration being positively related and repetition negatively related to total sickness). This was true over diverse systems and large subject pools. This result verified the generalizability of the relationships among sickness, exposure duration, and repeated exposures. Additional research is indicated to determine the optimal length of a single exposure and the optimal intersession interval to facilitate adaptation.

This paper proposes a theoretical model of wayfinding that can be used to guide the design of navigational aiding in virtual environments. Based on an evaluation of wayfinding studies in natural environments, this model divides the wayfinding process into three main subprocesses: cognitive mapping, wayfinding plan development, and physical movement or navigation through an environment. While this general subdivision has been proposed before, the current model further delineates the wayfinding process, including the distinct influences of spatial information, spatial orientation, and spatial knowledge. The influences of experience, abilities, search strategies, motivation, and environmental layout on the wayfinding process are also considered. With this specification of the wayfinding process, a taxonomy of navigational tools is then proposed that can be used to systematically aid the specified wayfinding subprocesses. If effectively applied to the design of a virtual environment, the use of such tools should lead to reduced disorientation and enhanced wayfinding in large-scale virtual spaces. It is also suggested that, in some cases, this enhanced wayfinding performance may be at the expense of the acquisition of an accurate cognitive map of the virtual environment being traversed.

Cybersickness is a pervasive and deleterious effect of human-virtual environment interaction. This paper applies motion-sickness adaptation theory to cybersickness in virtual environments to determine if the degree of user-initiated control can suppress sickness. It is suggested that if users are allowed some level of control over their movement within a virtual environment, cybersickness will not be as severe as that resulting from an enviornment in which users must follow a predetermined (i.e., scripted) path of movement. While past motion-sickness studies have examined control versus no control, the present study focuses on modifying the level of user-initiated control such that it matches the needs of the task characteristics while minimizing sickness. The degree of user sickness was tested under passive, active, and active-passive control scenarios. As measured by the Simulator Sickness Questionnaire, the active (i.e., complete control) condition reduced the severity of the symptoms experienced as compared to the passive (i.e., no control) condition, but did not do so as completely as the active-passive (i.e., coupled control) condition. The implication is that the level of user-initiated control can be manipulated to modify the deleterious effects of human-virtual environment interaction.

Virtual environments are envisioned as being systems that will enhance the communication between humans and computers. If virtual systems are to be effective and well received by their users, considerable human-factors research needs to be accomplished. This paper provides an overview of many of these human-factors issues, including human performance efficiency in virtual worlds (which is likely influenced by task characteristics, user characteristics, human sensory and motor physiology, multimodal interaction, and the potential need for new design metaphors); health and safety issues (of which cybersickness and deleterious physiological aftereffects may pose the most concern); and the social impact of the technology. The challenges each of these factors present to the effective design of virtual environments and systematic approaches to the resolution of each of these issues are discussed.