A Comparative Study Between Wired and Wireless Virtual Reality Setups

Virtual Reality (VR) through head-mounted displays (HMDs) can be delivered via multiple setups such as smartphones, standalone VR or VR Workstations. The VR Workstation setup delivers the best performance of them all; however, as a drawback up until recently, it required cables to power up the VR equipment. The introduction of wireless solutions for VR Workstations came to solve one of the disadvantages of this setup. However, the impact of the wireless solution versus the HMD cables was not yet properly investigated. In this paper, we study the impact of using a wired vs wireless HMD on Presence, Cybersickness, and Game Experience. We conducted a quasi-experimental between-subjects study with 68 participants assigned to the following three groups that were balanced regarding gender and sample size: Cable (participants used a wired HMD), Cable + Help (a researcher assisted the participants with the HMD cable during the experience to reduce the participants' awareness of it), and Wireless (untethered HMD). Results showed no significant differences in presence and cybersickness. The game experience was significantly different, with Cable + Help performing better than Cable and Wireless. We conclude that sense of presence using wireless solutions is equated to wired HMD solutions.

SECTION I. Introduction

Virtual Reality (VR) has been evolving since the prototypes [1]–​[3] into the widespread success that it is today. Up until recently, VR Headsets or Head-Mounted Displays (HMD) were wired, usually to computers, to ensure enough computational capability so the VR unit can properly deliver the virtual experience (VR Workstation). One fact is that the presence of cables is not of much importance if users would experience VR while sitting or standing without physical movements. However, the evolution of VR applications is towards experiences that require freedom of movements in 6-DOF (degrees of freedom) over a wide tracking area. In such a scenario, wireless solutions would be preferable since the HMD cable can compromise the VR experience by, for instance, making users trip over it or getting wrapped.

A. Presence

The concept of presence has been defined differently throughout the literature [4]–​[18]. However, a widely accepted definition of Presence and one which we follow in this work is Slater’s definition [14]: presence is a state of consciousness, a psychological sense of being in the virtual environment (VE). This is considered one of the most important aspects of VR — the possibility for users to develop an intense sense of Presence. This sense of Presence will result in users behaving more realistically in the virtual environments [14], [19]–​[21]. The measurement of presence has been used in several works to evaluate VR applications. The search for the knowledge of what affects the presence and how is presence developed is one of the most researched topics in this field [4], [5], [9], [16].

B. Immersion

The term immersion is often used alongside presence as being the same thing. In this work, we make the distinction between presence and immersion. Immersion is the level to which the technology can recreate a rich and credible virtual experience by successfully shutting out reality [14]. Immersion is objective, unlike Presence. A more immersive system offers better conditions for users to feel more present. Following this line of thought, the cable is an element that can distract users, and remind them of their surrounding reality. Therefore, by providing a wireless experience, we are raising the immersion of the system and thus, the probability of users feeling more present.

C. Cybersickness

Complementary to Presence and Game Experience, Cybersickness is an important factor to take into account. In previous user studies, we have observed that using large areas and real walking leads users to get wrapped in the HMD cables by the constant turning around, users would often turn 360° degrees to unwrap themselves from the cables. This constant turning may cause Cybersickness symptoms. These are motion sickness like symptoms that occur in VR, usually when the vestibular and visual systems conflict with each other [22], [23]. For example, if we are looking down reading a book while traveling on a bus, our visual system will not pick up cues that we are moving while our vestibular system will sense that we are. The conflict between the visual and vestibular will result in motion sickness. A similar phenomena can happen in VR, where we sense our body and head movement, but the tracking or computer cannot process correct visual stimuli in time (lag). Some of the symptoms that may arise from that are nausea, headaches, ocular discomfort, and disorientation.

D. Game Experience

Breaks in Presence and the constant reminding that users are acting in a virtual environment could also influence Game Experience. According to the GameFlow model [24], immersion is one of the elements that contribute to player enjoyment in games. An immersed player would “become less aware of their surroundings, less self-aware and less worried about everyday life or self”. Here, we can see how the constant interference of HMD cables can distract users out of the virtual experience and back to reality. Concentration could also be impacted, as players “should not be distracted from tasks that they want/need to concentrate on” and where the game should “quickly grab the player’s attention and maintain their focus throughout the game” between other criteria. We thus suspect that the VR wireless solution will improve Game Experience by reducing possible distractions and allowing players to maintain a better focus on what they are doing.

E. How Cables Impact the Virtual Experience

From previous studies, we have observed that the cable that connects the HMD to the computer was usually an “anchor point” to reality. Participants often stated at the end of the experience that sometimes the cable reminded them that they were in a virtual world. We also observed that some users were making 360° turns and other movements to avoid getting wrapped in the cables. We must note that this only happened in virtual experiences where participants used real walking metaphor (please refer to [25] for more details regarding real walking metaphor). We theorize that the cable may cause consistent breaks in Presence (events that remind users that they are in a virtual environment, breaking the illusion of “being there” [26], [27]).

In the literature, several studies also mention cables as being a potential problem. Davis et al. [23] discuss that general ergonomics need to be considered and refers to HMD cables as capable of distracting users from the experience.

Meehan et al. [28] pointed out that: “Additionally, we must eliminate the cables that tether subjects to the monitoring, tracking, and rendering equipment. Our subjects reported this encumbrance as the greatest cause of breaks in Presence.”

Rizzo and Kim [29] comment that: “Wires constrain interaction, both mentally and physically, and complex motion can result in the user getting tangled in wires and cables that limit usability and could create safety hazards.”

Slater and Steed [30] studied the mental transition of users between the virtual and real world. Participants were asked to point out the causes of this transition. Between several causes, participants pointed out that “Becoming aware of cable wrapped around the foot.”, “The cable brushing against my legs.”, and “Trapped in wires.” led them to transition from virtual environment to the reality.

Garau et al. [27] investigated breaks in Presence using a CAVE (Cave Automatic Virtual Environment). Authors stated that, among others, environmental factors related to the apparatus, contributed to breaks in Presence as participants found the 3D stereoscopic glasses uncomfortable. They follow up with a citation from a participant stating that “Maybe the sensation of this thing on the glasses, because I’m not very comfortable. The worry that I would step on the cable and break your equipment”.

To mitigate the effects of a wired solution, the retractable cable management solutions decrease the weight of the cables and avoid that the cable gets wrapped around the user. However, in these solutions, users can still pinpoint their location in the real world relative to the cable. Also, they require an already installed set of “hooks” in the ceiling that are less convenient if we want to change the VR setup to another place. Moreover, it is only possible to use this type of solution if we have a closed area with a ceiling at an acceptable height.

F. Advantages and Disadvantages of VR Wireless Solution

Wireless solutions can solve the problems that cables bring, but in contrast, they are not free of disadvantages. VR wireless solutions are usually based on VR smartphone headsets or dedicated standalone VR equipment. However, due to their reduced computational capability when compared to a VR Workstation, these solutions tend to have lower performance (which can result in lower simulation quality). Also, VR smartphones headsets use the built-in accelerometers and gyroscopes of the smartphones to track the head, which could be unreliable and only provide 3-DOF tracking. Only recently, wireless adapters for VR Workstations were made available and brought the possibility of using a VR Workstation with high-performance HMDs to deliver wireless VR experiences.

Due to technological limitations, some lag or inconsistencies could happen while transmitting a video signal at high framerates (near 90 frames per second) and high resolution ($1080\times 1200$ pixels per eye). A study was conducted in this regard, using the same equipment used in this study (TPCAST) [31]. Authors stated that freezes in video playback were uncommon and they did not notice freezes during regular usage. They also reported a frame-rate of near 90fps, which is the refresh rate of the HTC Vive.

Although the world is moving towards tetherless solutions, state of the art equipment with very high resolutions, refresh rates and other specifications will still need tethered connections as the time to market of new state-of-art wireless solutions is slow. Some high-end HMDs are still needing cables because of their throughput requirements.

G. Contribution

To the best of our knowledge, there are still no studies that focus on the benefits of wireless VR adaptors in interactive VR applications that require real-walking to navigate in demanding virtual environments. Therefore, in this work we aim to create knowledge about how much of an advantage the wireless solution can be against the standard wired HMD by studying Presence, Cybersickness and Game Experience in a between-subjects controlled study.

We hypothesize that the VR wireless solution will improve both Presence and Game Experience because the absence of cables will increase the system immersion, resulting in users to be less aware of the real world, less distracted and less worried about tripping over the cables.

Regarding Cybersickness, a constant turning around due to the cables could raise the probability of participants feeling these symptoms. However, we believe that this should not be significant to the point where removing the HMD cables from the experience would result in lower significantly lower Cybersickness.

Thus, we propose the following hypotheses:

• H1: Presence will be higher in the VR wireless solution.

• H2: The VR wireless solution will not influence Cybersickness.

• H3: Game experience will be higher in the VR wireless solution.

SECTION II. Methods

A quasi-experimental cross-sectional study of comparative nature following a between-group design was conducted to investigate the impact of the absence of HMD cables on Presence, Game Experience and Cybersickness.

A. Sample

We used a non-probabilistic sampling technique, namely, convenience sampling. The sample consisted of 68 participants (40 males and 28 females) aged between 16 and 49 ($M=21.43,\,\,SD=4.773$ ), mostly university students. The participants were divided between three groups (see autoref sec:variables), with 19 participants assigned to the first group, 23 to the second and 26 to the third group (evenly balanced between genders). The assignment of the participants to each group was made ensuring that sample size and gender was balanced between conditions. All participants were naive to the conditions of the experiment.

B. Variables

We considered the VR setup as the independent variable with three levels:

1. Cable ($N=19$ ): HMD with the original cable that runs from the headset to the computer

2. Cable + Help ($N=23$ ): HMD with the original cable and with a research team member managing the cable to minimize its interference on the virtual experience.

3. Wireless ($N=26$ ): HMD using the TPCAST Ⓡ wireless adapter [32] and power-bank. In this condition, participants can move freely without the interference of cables.

As dependent variables, the following were considered:

• Presence and its subscales (Spatial Presence, Experienced Realism, Involvement): The illusion of being in the virtual environment as being real. Presence was measured through the IPQp questionnaire [33].

• Cybersickness and its subscales (Nausea, Oculomotor discomfort, Disorientation): Motion sickness-like symptoms that can occur when visual and vestibular system enter in conflict. Cybersickness was measured through the SSQ questionnaire [34].

• Game Experience and its subscales (usability/playability, narratives, play engrossment, enjoyment, creative freedom, audio aesthetics, personal gratification, and visual aesthetics): The overall satisfaction players get from playing the game. Game experience was measured through the GUESS questionnaire [35].

C. Instruments

We collected data about Presence, Cybersickness and Game Experience through questionnaires, complemented with direct observation of how users behave during the experience and through a debriefing session after completing the questionnaires. As for the Presence, we used the validated Portuguese version of the Igroup Presence Questionnaire (IPQp) [33], [36]. The questionnaire uses a 5-point Likert scale with 14 items that results in the following subscales: spatial Presence (the feeling of being physically present in the virtual environment), experienced realism (the subjective experience of realism), involvement (the attention that is given to the environment and the level of involvement experienced) and Presence (the global sense of Presence).

Cybersickness was evaluated using the Portuguese translated version of the Simulator Sickness Questionnaire (SSQ) [34]. It’s composed of 16 items corresponding to various symptoms that are classified as none, slight, moderate or severe. The questionnaire includes the following subscales: nausea (nausea, salivation, burping, stomach awareness), oculomotor discomfort (eye strain, difficulty focusing, blurry vision), disorientation (vertigo and dizziness) and Cybersickness (global Cybersickness).

For the evaluation of Game Experience, we used the translated Portuguese version of the Game User Experience Satisfaction Scale (GUESS) [35]. This questionnaire has 55 questions, on a 7-point Likert scale regarding 9 factors of the gaming experience: usability/playability, narratives, play engrossment, enjoyment, creative freedom, audio aesthetics, personal gratification, social connectivity, and visual aesthetics. Because there was no social connectivity, this factor was removed from the analysis.

D. Materials

In this section, we describe the virtual reality game used as well as the immersive system apparatus. As such, we divided the materials into two subsections: software and hardware.

E. Software

We used a VR game developed by the research team using Unity^® 2017, named “Illusions”. The game aimed for an immersive experience, using real-walking [25] and so it presents a dark and scary ambient, depicting the interior of an abandoned hospital (1). The narrative focuses on the mystery of why is the player in that place and who he is. While progressing through the game the player learns that he/she is a schizophrenic patient. The game ends in a white cushioned room where the player realizes that it was all a hallucination and he/she never left the room.

The locomotion is achieved by using a real-walking metaphor in an area of $4\times 4$ meters. The level design was done in such a way that participants will not need to turn 180° degrees to continue walking through the game. Players will subtly walk in circles, giving the sensation that the VE is bigger than it is, and disorienting them regarding their orientation and localization in the real world. The level design is also symmetric, meaning that the player, when unlocking the door, can go left or right towards the next level with the same outcomes (Fig. 2).

FIGURE 1.

Screen shot of level 2 (illustrative example of the virtual environment, better visualised on screen).

FIGURE 2.

Levels layouts.

There are three floors, each one corresponding to one level. The player starts in the first level inside a room where he must find a key to unlock a door which will give the player access to a corridor. From there, the player can move to the next level by walking towards one of the two stairs, one on each side. Because the participants cannot physically climb stairs, when the player reaches the stair’s icon, he is teleported to the next level. In the second level, the player has to find a new key to unlock another door, which will give them access to a “pit room”. Here, the player reaches one of the two doors available by leaning on the edge of the room and side-walk towards the door. When opened, the player will be teleported to the next level. Again, he/she has to find a new key. To do so, the player has to find and interpret a code to open a safe. Inside the safe, lies one key to unlock the door, another to unlock a fuse box, a medical record sheet and photos of the game narrative. The player has then to open the door, catch two fuses, each one in the far side of the corridor, and insert them into the fuse box. This will power two elevators situated in the corridor which the player has to enter and where the game will finish. The game requires the player to explore the scene to find the keys. This involves a lot of movement, turning back and forth.

F. Hardware

The VR game was played on a Windows^® computer with the following specifications: CPU Intel^® Core™ i7-5820K @ 3.30GHz, 32GB RAM, Nvidia^® Geforce^® GTX 1080.

For the wired VR setup, we used the HTC^® Vive™ system, which has one cable that runs from the HMD to the computer. A cable extension was used to avoid participants running out of cable when reaching the far side of the play area.

For the wireless solution, we used the TPCAST^®, a wireless adapter for the HTC^® Vive™. The wireless solution requires a power bank to deliver power to the adapter and HMD, which was in a bag secured to the participants’ belt running a cable towards the HMD thought the back. The research team tested this wireless solution previously to verify its capabilities and to fine-tune it to avoid possible signal interference. From what we experienced, the VR wireless solution proved to be capable of handling all the data without significant problems. Differences in image quality were indistinguishable between wired and wireless. However, the image quality would degrade if the line of sight between the transmitter and receiver was blocked. To avoid this, the transmitter was placed near the ceiling to cover the full playing area and with a direct line of sight to the receiver. The research team did not notice latency or inconsistencies while using this wireless solution.

To deliver the audio, we used active noise-cancelling headphones connected to the HTC^® Vive™ 3.5 mm jack.

G. Procedure

Participants performed the experiment at a specialized Virtual Reality Laboratory. The laboratory’s experimental room allows the full control of variables such as light, temperature, ambient air circulation, as well as, soundproof walls and doors. As such, participants performed the experiments under the same environmental conditions.

Before beginning the experiment, participants filled a consent form and a brief questionnaire with their age and gender. Participants wore the HMD and headphones, and in the wireless condition, the power-bank secured to their waist with the help of a researcher to ensure proper equipment placement and participant’s comfort. All participants started the virtual experiment with the same orientation and position in the room. Subjects were not aware of what was being studied.

In the Cable condition, there was no help in managing the HMD cables, so participants would have to avoid wrapping themselves on the cable (Fig. 3). In the Cable + Help condition, a researcher would try to minimize the player awareness of the cable. This was done by strategically moving the cable without the participants’ knowledge. In the Wireless condition, players would move freely through the game due to the non-existence of a cable between the computer and HMD. It should be noted that regardless of the condition, there was always a researcher to provide physical support if participants would leave the play area (although limits were defined in the virtual environment), lose balance, or trip over the cable (when applicable).

FIGURE 3.

Participant performing the experience with HMD cables.

There was no time limit: the virtual experiment ended when participants reached the end of the game. Right after ending the virtual experiment, participants were asked to complete the IPQp, SSQ, and GUESS questionnaires and lastly an observations field to add optional additional information. In the end, we debriefed the participants to assess what they thought about the experience and any additional observations they might want to share with the goal of verifying if there were comments made regarding the existence of cables.

SECTION III. Results

All statistical procedures were performed using the IBM^® SPSS^® 24 software. A preliminary analysis of the data was conducted to verify outliers and normal distribution. A total of sixteen outliers were identified (through visual inspection of box plots) and removed. The distribution of participants after the removal of outliers were the following: Cable ($N=16$ ); Cable + Help ($N=14$ ); Wireless ($N=22$ ). The data from 52 participants (27 male and 25 female) was analyzed.

All the dependent variables regarding presence and game experienced were normally distributed ($|Skewness| < 2$ and $|Kurtosis| < 2$ ). Therefore, parametric statistics were used, namely Analysis of variance (ANOVA). The Levene test was performed to evaluate the ANOVA homogeneity assumption. The subscales usability/playability, Enjoyment, Audio Aesthetics, Visual Aesthetics, and Final Score violated the homogeneity assumption, thus, for these subscales, a Welch ANOVA was performed.

Some cybersickness scores did not follow a normal distribution, thus non-parametric statistical tests were used to compare the different groups, namely the Kruskal-Wallis H test.

A. Presence

No statistically significant differences were found between the experimental groups for Spatial Presence ($F(2, 49)=1.017; p=0.369; \eta _{p}^{2} = 0.040; OP=0.217$ ), Experienced Realism ($F(2, 49)=1.388; p=0.259; \eta _{p}^{2} = 0.054; OP=0.284$ ), Involvement ($F(2, 49)=0.973; p=0.385; \eta _{p}^{2} = 0.038; OP=0.210$ ) and overall Presence ($F(2, 49)=1.411; p=0.254; \eta _{p}^{2} = 0.054; OP=0.288$ ) as shown in the autoref Table 1.

TABLE 1 IPQp Subscale Score Means, Standard Deviations, and ANOVA Statistical Test Results for Each Presence Subscale on Each Condition. Subscale Means Range From 1 to 5 With Higher Values Being Better

B. Cybersickness

As assessed by visual inspection of boxplots, distributions of Cybersickness scores for all its subscales were similar between the groups. No statistically significant differences for Nausea ($\chi ^{2}(2) = 0.100, p = 0.951$ ), Ocular Discomfort ($\chi ^{2}(2) = 0.469, p = 0.791$ ), Disorientation ($\chi ^{2}(2) = 0.939, p = 0.625$ ) and overall Cybersickness ($\chi ^{2}(2) = 0.396, p = 0.820$ ) were found between the three groups (Table 2).

TABLE 2 SSQ Subscale Score Means, Standard Deviations for Each Experiment Condition, and Kruskal-Wallis H Statistical Test Results. Scores Range From 0 to 201, 160, 293 and 2437 (Nausea, Oculomotor Discomfort, Disorientation, and Cybersickness Respectively). Lower Values are Better

C. Game Experience

Statistically significant differences were found for Creative Freedom ($F(2, 49)=6.548; p=0.003; \eta _{p}^{2} = 0.211; OP=0.891$ ), Audio Aesthetics ($F(2, 29.116) = 9.000; p = 0.001$ ), Visual Aesthetics ($F(2, 30.537) = 4.332; p = 0.022$ ), and Final Score ($F(2, 30.003) = 8.993; p = 0.001$ ) (Table 3).

TABLE 3 GUESS Subscale Score Means and Standard Deviations, Significance Level, and ANOVA Statistical Test Results for Each Game Experience Subscale on Each Condition. For Welch’s ANOVA Only the Significance Level is Presented. Subscales Range From 0 to 6 With Higher Values Being Better. The Final Score is the Sum of All Subscales

To identify the conditions where the differences lie, we followed up with a Bonferroni post-hoc analysis for the scales with homogeneity of variance. For the rest, Games-Howell post-hoc was used.

The differences in the Creative Freedom scale lied between the conditions: Cable– Cable + Help ($p=0.021$ ) and Cable + Help– Wireless ($p=0.003$ ). Creative freedom was significantly higher in Cable + Help ($M=5.524$ , $SD=0.517$ ) than Cable ($M=4.783$ , $SD=0.764$ ) and Wireless ($M=4.672$ , $SD=0.787$ ) conditions.

Audio Aesthetics scores were higher ($p=0.001$ ) in Cable + Help ($M=5.893$ , $SD=0.189$ ) than in the Wireless condition ($M=5.474$ , $SD=0.407$ ).

Visual Aesthetics scores were higher ($p=0.016$ ) in Cable + Help ($M=5.762$ , $SD=0.242$ ) than in Wireless ($M=5.439$ , $SD=0.416$ ) condition.

Final score was statistically different between: Cable– Cable + Help ($p=0.007$ ) and Cable + Help– Wireless ($p=0.004$ ). Scores were higher in Cable + Help ($M=44.044$ , $SD=1.605$ ) than in Cable ($M=40.657$ , $SD=3.614$ ) and Wireless ($M=41.714$ , $SD=2.442$ ) conditions.

D. Anecdotal Evidence

Although no significant difference was found, we observed different user behaviors towards the Presence of the HMD cable. When participants sensed they were getting trapped in the cables by a constant turning around, they would purposely turn the other way around (almost doing a 360° rotation) to get rid of the cable. Some also used their hands and arms to move away from the cable from their path to make sure they would not trip over it.

Some participants stated in the observations field of the questionnaire that to improve the virtual experience, the cable would have to be removed. Some of the comments given by the Cable condition participants were: “If possible, reduce the cables of the VR setup, the fear of tripping and falling over them is big and prevents us from totally losing consciousness of the real world”, “The HMD cable perturbed a little”, “A headset without cables would help to improve the experience”, and “The cable was always present and cause us to react to the real world”. This suggests that some users did notice the interference of the cable enough to suggest removing it, however, its impact in the overall Presence, Cybersickness, and Game Experience was not significant.

SECTION IV. Discussion

In this section, results are discussed regarding our hypotheses and their implications in the field. We divided the discussion to focus Presence, Cybersickness and Game experience individually.

A. Presence Analysis

We suggested in H1 that Presence scores would be higher in the VR wireless solution. Such was due to the wireless solution offering a more immersive system by allowing increased freedom of movement without an interfering element connecting users to the real world. However, Presence scores led us to not accept this hypothesis. Even though users noticed the cable (as observed in their behavior and comments in the questionnaire), its absence did not cause a significant difference in Presence scores.

During the wireless condition, we noticed some instability in the wireless connection in a few participants. Some times the HMD would lose image and sound during a short period of time (around three seconds). However, these occurrences were rare. This seemed to happen randomly, despite our best efforts to minimize interference of the signal in the room. These “blackouts” can be considered as breaks in presence. Garau et al. [27] studied how whiteouts affected the subject’s transition from VR back to reality. The authors blanked out the CAVE four times throughout the experiment, each time for two seconds. These induced whiteouts were very similar to the blackouts some participants experienced in this work. In their work participants noticed and perceived the whiteouts as breaks in presence. The first whiteout was considered the most impactful, with the following being less pronounced. Participants were able to recover their sense of presence after the breaks of presence. However, the time needed to recover was longer for each successive whiteout.

Although the blackouts might have influenced Presence, we argue that they were not the main cause for the lack of significant differences as they occurred rarely for brief seconds on an experience that took approximately 15 minutes. So there was time for users, that experienced the blackout, to recover their sense of Presence.

Overall, we observed the HMD cable interfering in the experience more often than the wireless solution did when it momentarily failed. Such leads us to believe that the wireless solution still should provide a better experience than using wired solutions.

B. Cybersickness Analysis

It was expected that the Wireless condition would not influence Cybersickness scores in H2. This was due to a previous study [31] where it was concluded that the TPCAST was able to provide the visual stimuli without freezes and also due to preliminary tests the research team did, where no lag between the user input and the corresponding output of the stimuli to the HMD was noticed. The results showed no significant differences between conditions which suggest that wireless solutions could be used without any additional Cybersickness interference.

C. Game Experience Analysis

From a Game Experience perspective, we aimed to study if playing without HMD cables would be significantly better as we hypothesized in H3. The results demonstrated that Creative Freedom, Audio Aesthetics, Visual Aesthetics, and Final scores were higher in the Cable + Help condition. Such results indicate that it is better for the participant game experience to have someone to manage the cables than simply leaving the users to manage themselves. Such could be easily justified by the fact that in Cable + Help condition, users are a lot less aware of the cable and can better focus on the experience itself.

Subjects were not aware of the fact that a researcher would help them with the cable. Although, there is the possibility that during the experience, knowing that there were cables and they were not interfering, subjects might have started to assume someone was helping and maybe started to feel more “safe”, worrying less with their real surroundings, focusing more attention in the VR. However, no participants commented on such.

Wireless was expected to improve over the Cable+Help. However, results indicated that such was not the case. A similar justification for the differences between Cable and Cable + Help might apply. Subjects might felt more insecure by using a wireless solution because they were not aware if someone was watching over them. Such could cause subjects to allocate part of their attention to the real environment to avoid damaging the equipment by colliding with real objects. Previous studies in the literature [27], [29] stated some concerns about subjects possibly damaging experimental apparatus.

However, if such was the reason for the Cable + Help outperforming the other conditions, then presence scores should also have reflected it. More studies are needed to verify the proposed justification and to verify why the game experience was significantly different and presence was not.

SECTION V. Conclusion

In this work, we aimed to study the impact of HMD cables in the Presence, Cybersickness and Game Experience by comparing three conditions (Cable, Cable + Help, and Wireless) using a VR game focused in freedom of movement that makes use of real walking as navigation metaphor.

Theoretically, the less the impact of the cable, the more immersive the VR system is, and the better are the conditions for subjects to feel more present and to have better game experience. The results showed that there were no differences in Presence and Cybersickness, but some subscales as well as overall score of Game Experience were found to be higher in Cable + Help than in other conditions.

The results indicated that the sense of presence on wireless solution is equated to wired ones. As such, researchers could compare this metric between their studies using wireless solutions against wired HMD. For example, in terms of Presence, researchers can discuss that the cause of the improvement was not the wireless setup but another variable that was being studied.

The wireless solution did not invoke more cybersickness symptoms than in wired HMD. This led us to conclude that the wireless solution is capable to receive the user input and deliver the correct feedback avoiding possible sensory conflicts. Therefore, Presence and Game Experience scores could not have been influenced by such symptoms.

Results indicated that Game Experience was rated significantly better in the Cable + Help. Although more studies are needed to confirm this, subjects might have realized that a researcher was present in the experimental room watching over their movements, which could have increased the sense of security of subjects. Such could have led them to worry less about their real surroundings and concentrate their attention in the virtual reality game.

Based on the anecdotal evidence, the wireless solution presents an advantage towards the standard HMD setup. Users are less likely to trip or get wrapped up in the cables, as well as researchers don’t have the need to supervise participants so closely to ensure they would not fall or disconnect the equipment by stretching the cables. However, signal interference presents a problem that has to be solved and controlled before fully adopting wireless solutions.

Additional studies are needed to verify the extent to which participants were aware of the fact that someone was helping with the cables in the Cable + Help condition and evaluate how worried participants were about the cables in the conditions featuring tethered HMD. User performance could also be taken into account in future work to verify how well users perform between conditions. To improve this study furthermore, new wireless modules and HMDs should be taken into account and evaluated as they are released to the market, to verify what improvement they may bring.