ISASE 2024

Drone Rider: Effects of Translucent Actual Own Body Parts onEmbodiment in Virtual Reality Space
Hong SHEN *, Kazuya SHIMATO *, Yuta GOTO *, and Shogo OKAMOTO ** Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-shi, Tokyo 191-0065, Japan

Abstract: In virtual reality (VR) systems, particularly in practical applications such as simulators, enhancing the sense of embodimentis crucial to minimizing the disparity between virtual and real-world experiences. This study investigated the effects of viewing theoperator's own body parts, either clearly or translucently, on embodiment. For this purpose, we employed a VR drone simulator, inwhich the operator rode on a drone and enjoyed flying over natural landscapes. The operators compared three conditions regarding thevisual representation of their own hands on a grip. In one condition, they could see their own hands overlaid on the VR scene. In
another condition, the overlaid hands were made translucent. These conditions were achieved by using the video-see-through functionof a VR headset. In the last condition, the hands were not visible. Through a user study, we compared the sense of embodimentexperienced in the three conditions. Embodiment was marginally enhanced when the actual forearms appeared translucently on thecomputer graphics images, compared to the condition where the operators’ forearms were not visible. Viewing one’s own body partsin a translucent form can improve user experiences in VR environments.
Keywords: Virtual reality, See-through, Flight simulator

1. INTRODUCTION
2. SYSTEM OF DRONE RIDER
The authors are developing a virtual reality (VR)system named Drone Rider [1], in which operators ride on
a virtual drone and soar above magnificent landscapes or
fly through urban skyscrapers to compete with others.
This system has been utilized to develop and test
techniques aimed at making VR systems more immersive.
For immersive virtual reality systems, earlier
researches delved into various aspects, such as perspective,
revealing that a first-person perspective condition is more
effective for sensing body ownership of the avatar’s bodysegments in VR spaces than a third-person perspective
condition [2–4]. Other studies demonstrated that thevirtual hand felt as though it belonged to the operator’s
own body in a mixed reality condition [5, 6]. These studies
suggest a possibility: when the actual body images of theoperator are visible in the virtual reality scene from a firstperson perspective, the embodiment may be experienced
more intensely. Thus far, no studies have directly
addressed this question.
We hypothesized that the visibility of the operator’s
actual hands holding the grip handle of a drone enhances
the sense of embodiment and immersion during VRexperiences. To test this, we examined the influence ofoverlaying images of the operator’s real hands on theimmersive experiences.

2.1 Hardware system
The apparatus primarily consisted of a VR headset(Meta Quest Pro, Meta Platforms, Inc., USA), a
trampoline (Honei, China), and a vibratory footplate, asillustrated in Figure 1 [1]. The drone’s flight direction wasdetermined by the angular motion of the VR headset,
corresponding to the operator’s weight shift. For instance,to fly forward, the operator would lean forward on thetrampoline, and the drone’s speed would change linearlyFig 1: Overview of Drone Rider. Adapted from [1].

1Figure 2: Three visual conditions. a) Overlaid condition, where own hands are clearly seen. b) Translucent condition, where VR
scenes are seen through own hands. c) No see-through condition.

3.2 Stimulus conditions
The experiments were conducted under three different
see-through conditions. In one condition, the operator’sforearms and grip handle were clearly seen, as shown in
Figure 2 (a). In another condition, these images weretranslucent and VR images could be seen through them,as in Figure 2 (b). In the remaining condition, the seethrough function was not used, as in Figure 2 (c). The
operator’s forearms and handle were not seen in thiscondition.

with the VR headset’s inclination. Additionally, a fan wasused to simulate wind effects in accordance with thedrone’s speed.
The operator stood on a footplate attached to thetrampoline while holding a safety handle. When theoperator shifted their center of body mass, the footplatepassively inclined in the roll and pitch directions. This
inclination matched the state of the virtual drone, ensuring
congruency between the visual and vestibular stimuli.
Two voice-coil motors (Vp7, Acouve Laboratory Inc.,Japan) were installed on the footplate’s surface. They
delivered the vibration generated by the drone’s propellers
to the operator’s entire feet and legs [1].

3.3 Procedures
Before conducting the experiment, participants
practiced piloting the drone to become familiar with itscontrols. The practice session lasted until participants felt
comfortable, typically ranging from 1 to 2 minutes. They
utilized the overlaid hand condition to simulate theexperiment’s conditions.
In the main experiment, participants freely maneuvered
the drone in the sky above a field for one minute. They
were encouraged to steer the drone around the yaw axis
unless they experienced motion sickness. The three
conditions were administered in random order toindividual participants, with each condition beingexperienced once. A break of 1.5 minutes was provided
between trials.
Immediately following each trial, participants
responded to questionnaire items listed in Table 1. Each
item was rated on a scale from 0 to 9, where 0 indicated

2.2 Software system
Unity (2021.3.21f1) was utilized to develop the drone
simulator. The tilt of the VR headset was linearly
converted to the drone’s velocity. The drone’s
forward/backward speed was determined by the pitch
angle of the VR headset, while the tilt around the roll axis
influenced the drone’s yawing velocity. The operator
could see the drone that s/he was on board while flying thesky over a natural field.
Using the see-through feature provided by Meta
Platforms, Inc., the operator’s forearm and the handle
were integrated into the VR environment. As illustrated inFigure 2, the images of the operator’s forearms and handle
were overlaid onto the VR images and were updated inreal-time. The opacity or translucency of the overlaid
images could be adjusted.

Table 1: Questionnaire items

3. USER EXPERIMENT
Q1
3.1 Participants
Eight university students (six males and two females)in their 20s participated in the experiment after providing
a written informed consent.

Q2
Q3

2

Questionnaire
Were you able to pilot thedrone as you wanted?
Did you feel like you wereriding on the drone?
During the experience, did you
feel immersed in the VRspace?

Category
AgencyImmersion
Immersion

no applicability and 9 indicated intense applicability
throughout the experience. The questionnaire included
items related to the sense of agency and immersion, withthe sense of agency referring to the feeling of being able
to control a seen object—in this case, the drone. This
concept is explored in studies of body awareness in bothactual [7, 8] and VR [9–11] settings.

(a) Q1: Agency

N.S.
(d = 0.591)

Subjective score

N.S.
(d = 0.166)

3.3 Data analysis
We compared the three conditions across each of thethree questionnaire items using one-sample t-tests. Given
the small number of participants in the preliminary study,
we also referred to Cohen’s d, an effect size measure fort-tests. This value assesses the difference between two
groups without being influenced by the sample sizes.
When the d value is greater than 0.5, the difference ineffects between the two conditions is considered medium
or large [12].

840Clearhands(b) Q2: Immersion

Translucent
hands

Subjective score

p = 0.049(d = 0.837)

840ClearhandsTranslucent
hands(c) Q3: Immersion

N.S.
(d = 0.707)

Subjective score

N.S.
(d = 0.045)

4. DISCUSSIONNo
see-throughN.S.
(d = 0.223)

N.S.
(d = 0.444)

3.4 Results
The results of the analysis are shown in Figure 3.
Regarding Q1 (Were you able to pilot the drone as youwanted?), that is, the sense of agency, the scores for thetranslucent condition was marginally greater than thosefor the no see-through condition (p = 0.033 without
Bonferroni correction). The Cohen’s effect size was d =0.935 and large.
For Q2 (Did you feel like you were riding on thedrone?), the translucent condition was marginally greaterthan the no see-through condition, exhibiting p = 0.0499.
The Cohen’s effect size was d = 0.837 and large.
For Q3 (During the experience, did you feel immersedin the VR space?), no remarkable differences wereobserved between the conditions. Nonetheless, thereported immersion tended to be relatively large under theno video see-through condition.

p = 0.033(d = 0.935)

No
see-throughN.S.
(d = 0.309)

840ClearhandsTranslucent
hands

No
see-throughFigure 3: Comparison of questionnaire scores among thethree conditions. (a) Q1: Agency. (b) Q2: Immersion. (c)Q3: Immersion.

The translucent condition significantly improved thesense of agency in Q1 and the sense of immersion in Q2.
This improvement may be attributed to the visible realistic
arms being positioned where they were expected, leading
to participants feeling that they were piloting the dronewith their actual forearms. In contrast, we did not observea substantial increase in the ratings for Q1 and Q2 under
the condition where the arms were clearly visible. In thiscondition, the feet and trampoline were also clearly visible,
which might have diminished the sense of immersion in
the VR environment.

Regarding Q3, which pertains to the question about
immersion, the average score of the participants tended to
be low under the see-through conditions. Someparticipants commented that viewing their actual bodyparts in the virtual scenes could deteriorate theirimmersion into the virtual space. The acceptability of themixed reality condition may vary among individuals.

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5. CONCLUSIONS
We investigated the impact of visually incorporating theoperator’s own body parts into the VR environment on thesense of agency and immersion. Utilizing a drone-riding
simulator, the translucent visualization of the operator’s
actual arms and hand grip appeared to enhance both thesense of agency over the drone and, the sense ofimmersion, although the statistical significance of thesefindings was marginal due to the small sample size in thepreliminary experiment. Despite this limitation, the results
indicate that integrating the operator’s body parts into theVR space through a see-through function can effectively
enhance the immersive quality of VR experiences. Future
research should focus on refining projection methods andinclude a larger participant pool to validate these findings.
ACKNOWLEDGMENT
This paper was in part supported by MEXT Kakenhi(23H04360).
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