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Although it is widely believed that the sense of presence increases with increasing FOV, there is little published research which bears directly on this question. An experiment compared two viewing conditions for an immersive virtual environment: visual scene masking at the eye (60° FOV) and an unmasked screen (105° FOV). A significantly higher presence was found for the wider FOV.

1.0 Introduction

While it is generally believed that a wider field-of-view (FOV) encourages a higher sense of presence, of "being in" a virtual environment, few studies have been published which bear directly on this question. Hatada, Sakata & Kusaka (1980) looked at this issue for a wide-screen display using a subjective measure and an objective measure based on perceived tilt, concluding that "a visual display with horizontal viewing angles ranging from 30° to 100° and vertical angles ranging from 20° to 80° produces psychological effects that give a sensation of reality." They reported a positive relation between FOV and the "sensation of reality" (presence). The relation between FOV and performance (Piantanida, Boman & Larimer, 1992; Wells & Venturino, 1990) and geometric FOV and presence (Hendrix & Barfield, 1995) have also been studied.

We describe here an experiment which investigated the role of FOV on the sense of presence. The experiment was a preliminary experiment for a more comprehensive study on the role of foreground/background manipulations on presence (Prothero, Hoffman, Parker, Furness & Wells, 1995).

2.0 Method

38 high school students, ages 16-18 including 18 females and 20 males, completed the experiment. There were no participant selection criteria beyond the ability to see the visual display. Nearly all participants were new to virtual environments; none of the the participants reported more than 10 minutes prior experience.

Participants were exposed to the "Sharkworld" virtual environment, which was developed by Division, Ltd. and features a texture-mapped underwater scene with a sunken ship and various moving sea creatures. The participants tried to catch sharks using a virtual net which followed real hand position.

The environment was run on a Division ProVision 100 and was displayed using a Division dVisor HMD with the following FOV: 40° vertical, 105° horizontal combined across two eyes and 40deg overlap. Sound cues were not used.

The experiment used an eye mask (foreground occlusion) which limited the participant's FOV to a central circle. As this occlusion was close to the eye translation of the pupil during eye rotation, there was a difference between direct FOV (the range one can foviate on by turning the eyes but not the head) and peripheral FOV (the total range one can see using peripherlal vision while looking straight ahead without turning the head). We measured direct FOV for the foreground occlusion at 40 deg, peripheral at 60 deg. The foreground occlusion was provided by a pair of Lucas Products Corporation white "Super Sunnies" tanning goggles from which the 1.27 cm diameter central ultraviolet protectors had been removed. To avoid infection, the goggles were washed with rubbing alcohol between participants.

Unrestricted FOV was compared with FOV limited by the tanning goggles. Each participant was run for 2.5 min in each viewing condition with condition order counterbalanced. After each viewing condition, subjects completed a 5-item questionnaire including the following:

1. In sharkworld, I flet like ... (1 = I was standing in the laboratory, wearing a virtual reality helmet.) (7 = I was in some sort of ocean, near a shark-infested shipwreck.)

2. How real did the virtual world seem to you? (1 = about as real as an imagined world.) (7 = indistinguishable from the real world.)

3. To what extent were there times when you felt that the virtual world became the "reality" for you, and you almost forgot about the real world outside? (1 = at no time.) (7 = almost all the time.)

4. Did the virtual world seem more like something you saw or someplace you visited? (1 = something I saw.) (7 = some place I visited.)

5. Did the virtual world seem more like a picture or more like a scene looked at through a window? (1 = like a picture.) (7 = like looking through a window.)

The reliability of subjective measures of presence, such as the above questionnaire, is addressed in Prothero, Hoffman, Parker, Furness & Wells (1995).

3.0 Results

The questions were designed so that larger response values indicated greater "presence" or "immersion" in the virtual environment. Responses were analyzed separately for each question; also, the responses across all 5 questions were pooled for further analysis. Statistical evaluation used the non-parametric Wilcoxon signed-rank test.

The "presence" responses averaged across all five questions were smaller (Z = -2.4, p = 0.02) for the eye masking condition (M = 3.6, SD = 1.2) than for the no-obstruction condition (M = 4.2, SD = 1.2). When the responses to each question were analyzed separately, a significant difference between viewing conditions was found only for questions 1 and 2 (Z = -2.3, p = .02; Z = -2.9, p = .001), with near significance for questions 3, 4 and 5 (Z = -1.9, p = .06; Z = -1.4, p = .15; Z = -1.6, p = .10, respectively).

Further analysis revealed a significant difference between viewing conditions for females (Z = -2.2, p = .03) but not for males (Z = -.92, p = .36). An order effect was also found: averaging across all questions and both genders, the difference between viewing conditions was significant when subjects ran first in the eye masking condition (Z = -2.1, p = .03), but not when they ran first in the no-obstruction condition (Z = -.81, p = .41). Due to imperfect counterbalancing, the possible gender by order interaction could not be analyzed.

4.0 Discussion

The results of the experiment indicate a higher degree of presence with a wider field-of-view. As was shown in Prothero, Hoffman, Parker, Furness & Wells (1995), a foreground occlusion (the tanning goggles) results in a higher sense of presence, for the same field-of-view, than a background occlusion (paper taped to the HMD screen). We would therefore expect the difference between conditions to be more marked if the field-of-view restriction had been implemented as a background occlusion.

5.0 Acknowledgments

This research was supported in part by the Air FOrce Office of Scientific Research (contract #92-NL-225 and INST PROP NO:78216). The Division equipment used was paid for by the US West Foundation. We would like to thank the students and faculty at Garfield High School who participated in this experiment. The assistance of HITL staff and students is also gratefully acknowledged.

6.0 References

Hatada, T., Sakata, H. & Kusaka, H. (1980). Psychophysical analysis of the "sensation of reality" induced by a visual wide-field display. SMPTE Journal, 89, 560-569.

Piantanida, T.P., Boman, D., Larimer, J., Gille, J., & Reed, C. (1992). Studies of the field-of-view/resolution trade-off in virtual reality systems. In Vol. 1666 Human Vision, Visual Processing, and Digital Display III. Bellingham, WA:SPIE-The International Society for Optical Engineering.

Prothero, J.D., Hoffman, H.G., Parker, D.E., Furness III, T.A., & Wells, M.J. (1995). Foreground/Background Manipulations Affect Presence. Proceedings of the Human Factors and Ergonomics Society 39^th Annual Meeting. Santa Monica, CA:Human Factors Society.

Wells, M.J. & Venturino, M. (1990). Performance and head movements using a helmet-mounted display with different sized fields-of-view. Optical Engineering, 29, 870-877.