Woodrow Barfield

Effect of roadway geometrics and environmental factors on rural freeway accident frequencies.

This paper explores the frequency of occurrence of highway accidents on the basis of a multivariate analysis of roadway geometrics (e.g. horizontal and vertical alignments), weather, and other seasonal effects. Based on accident data collected in the field, a negative binomial model of overall accident frequencies is estimated along with models of the frequency of specific accident types. Interactions between weather and geometric variables are proposed as part of the model specifications. The results of the analysis uncover important determinants of accident frequency. By studying the relationship between weather and geometric elements, this paper offers insight into potential measures to counter the adverse effects of weather on highway sections with challenging geometrics.

Presence within virtual environments as a function of visual display parameters

This paper reports the results of three studies, each of which investigated the sense of presence within virtual environments as a function of visual display parameters. These factors included the presence or absence of head tracking, the presence or absence of stereoscopic cues, and the geometric field of view used to create the visual image projected on the visual display. In each study, subjects navigated a virtual environment and completed a questionnaire designed to ascertain the level of presence experienced by the participant within the virtual world. Specifically, two aspects of presence were evaluated: (1) the sense of being there and (2) the fidelity of the interaction between the virtual environment participant and the virtual world. Not surprisingly, the results of the first and second study indicated that the reported level of presence was significantly higher when head tracking and stereoscopic cues were provided. The results from the third study showed that the geometric field of view used to design the visual display highly influenced the reported level of presence, with more presence associated with a 50 and 90° geometric field of view when compared to a narrower 10° geometric field of view. The results also indicated a significant positive correlation between the reported level of presence and the fidelity of the interaction between the virtual environment participant and the virtual world. Finally, it was shown that the survey questions evaluating several aspects of presence produced reliable responses across questions and studies, indicating that the questionnaire is a useful tool when evaluating presence in virtual environments.

Statistical analysis of accident severity on rural freeways

The growing concern about the possible safety-related impacts of Intelligent Transportation Systems (ITS) has focused attention on the need to develop new statistical approaches to predict accident severity. This paper presents a nested logit formulation as a means for determining accident severity given that an accident has occurred. Four levels of severity are considered: (1) property damage only, (2) possible injury, (3) evident injury, and (4) disabling injury or fatality. Using 5-year accident data from a 61 km section of rural interstate in Washington State (which has been selected as an ITS demonstration site), we estimate a nested logit model of accident severity. The estimation results provide valuable evidence on the effect that environmental conditions, highway design, accident type, driver characteristics and vehicle attributes have on accident severity. Our findings show that the nested logit formulation is a promising approach to evaluate the impact that ITS or other safety-related countermeasures may have on accident severities.

The sense of presence within auditory virtual environments

Two studies were performed to investigate the sense of presence within stereoscopic virtual environments as a function of the addition or absence of auditory cues. The first study examined the presence or absence of spatialized sound, while the second study compared the use of nonspatialized sound to spatialized sound. Sixteen subjects were allowed to navigate freely throughout several virtual environments and for each virtual environment, their level of presence, the virtual world realism, and interactivity between the participant and virtual environment were evaluated using survey questions. The results indicated that the addition of spatialized sound significantly increased the sense of presence but not the realism of the virtual environment. Despite this outcome, the addition of a spatialized sound source significantly increased the realism with which the subjects interacted with the sound source, and significantly increased the sense that sounds emanated from specific locations within the virtual environment. The results suggest that, in the context of a navigation task, while presence in virtual environments can be improved by the addition of auditory cues, the perceived realism of a virtual environment may be influenced more by changes in the visual rather than auditory display media. Implications of these results for presence within auditory virtual environments are discussed.

The effect of update rate on the sense of presence within virtual environments

The current study was done to investigate the effect of varying the update rate of a computer-generated simulation (5, 10, 15, 20, 25 Hz) on the sense of presence within stereoscopic virtual environments. Thirteen subjects navigated a virtual representation of Stonehenge and were asked to search for a rune, inscribed upon the wall of one of Stonehenges edifices. After performing the search task, subjects completed a questionnaire designed to assess their level of presence within the virtual environment. The results indicated that the subjective report of presence within the virtual environment was significantly less using an update rate of 5 and 10 Hz when compared to update rates of 20 and 25 Hz. Furthermore, the reported level of presence using a 15 Hz update rate was similar to the reported level of presence using update rates of 20 and 25 Hz thus indicating that computational resources could be saved using a slower update rate while maintaining a given level of presence. In addition, a factor analysis procedure indicated that the 13 questions designed to assess the subjects sense of presence within virtual Stonehenge could be grouped into three factors: (1) virtual presence, (2) navigation within the virtual environment, and (3) knowledge of real world surroundings while in the virtual world. Finally, comments on a descriptive model of presence within virtual environments are presented.

Comments on the use of olfactory displays for virtual environments

Currently, the hardware to produce virtual environments does not include olfactory displays, in spite of the fact that a wealth of sensory information is available from the olfactory sense. This paper reviews the physiological and psychological aspects of olfaction and discusses the use of olfactory displays for virtual environments. Further, it outlines the information that will be needed by the virtual environment research community to integrate olfactory stimuli into virtual environments.

Presence in virtual environments as a function of visual and auditory cues

The paper reports the results of two experiments each investigating the sense of presence within visual and auditory virtual environments. The variables for the studies included the presence or absence of head tracking, the presence or absence of stereoscopic cues, the geometric field of view (GFOV) used to design the visual display, the presence or absence of spatialized sound and the addition of spatialized versus non-spatialized sound to a stereoscopic display. In both studies, subjects were required to navigate a virtual environment and to complete a questionnaire designed to ascertain the level of presence experienced by the participant within the virtual world. The results indicated that the reported level of presence was significantly higher when head tracking and stereoscopic cues were provided, with more presence associated with a 50 and 90 degree GFOV when compared to a narrower 10 degree GFOV. Further, the addition of spatialized sound did significantly increase ones sense of presence in the virtual environment, on the other hand, the addition of spatialized sound did not increase the apparent realism of that environment.

Comparison of human sensory capabilities with technical specifications of virtual environment equipment

This paper presents the results of three surveys that compared the humans ability to detect and discriminate visual, auditory, tactile, and kinesthetic information with current technical specifications of virtual environment equipment. The comparison exposes limitations of current virtual environment interfaces and thus indicates areas where improvements in equipment design are needed. Furthermore, the paper presents basic definitions and units of measurement for sensory modalities, which also can be used to describe the capabilities of virtual environment equipment. Finally, the paper concludes with remarks concerning the relationship between the data presented in the three surveys and the design of virtual interfaces.

Evaluating the effectiveness of augmented reality displays for a manual assembly task

The focus of this research was to examine how effectively augmented reality displays, generated with a wearable computer, could be used for aiding an operator performing a manual assembly task. Fifteen subjects were asked to assemble a computer motherboard using four types of instructional media: paper manual, computer-aided, opaque augmented reality display, and see-through augmented reality display. The time of assembly and assembly errors were measured for each type of instructional media, and a questionnaire focusing on usability was administered to each subject at the end of each condition. The results of the experiment indicated that the augmented reality conditions were more effective instructional aids for the assembly task than either the paper instruction manual or the computer-aided instruction. The see-through augmented reality display resulted in the fastest assembly times, followed by the opaque augmented reality display, the computer-aided instruction, and the paper instructions respectively. In addition, subjects made fewer errors using the augmented reality conditions compared to the computer-aided and paper instructional media. However, while the two augmented reality conditions were a more effective instructional media when time for assembly was the response measure, there were still some important usability issues associated with the augmented reality technology that were not present in the non-augmented reality conditions.

Judgments of Azimuth and Elevation as a Function of Monoscopic and Binocular Depth Cues Using a Perspective Display

The purpose of this study was to investigate the use of three-dimensional display formats for judgments of spatial information using an exocentric frame of reference. Eight subjects judged the azimuth and elevation that separated two computer-generated objects using either a perspective or stereoscopic display. Errors, which consisted of the difference in absolute value between the estimated and actual azimuth or elevation, were analyzed as the response variable. The data indicated that the stereoscopic display resulted in more accurate estimates of elevation, especially for images aligned approximately orthogonally to the viewing vector. However, estimates of relative azimuth direction were not improved by use of the stereoscopic display. Furthermore, it was shown that the effect of compression resulting from a 45--deg computer graphics eye point elevation produced a response bias that was symmetrical around the horizontal plane of the reference cube, and that the depth cue of binocular disparity provided by the stereoscopic display reduced the magnitude of the compression errors. Implications of the results for the design of spatial displays are discussed.