0 Research

# Who’s Watching Me?: Exploring the Impact of Audience Familiarity on Player
Performance, Experience, and Exertion in Virtual Reality Exergames

Zixuan Guo
Xi’an Jiaotong-Liverpool University 0000-0002-0451-8988 Wenge Xu
Birmingham City University 0000-0001-7227-7437 Jialin Zhang
Xi’an Jiaotong-Liverpool University 0000-0001-6044-8585 Hongyu Wang
Xi’an Jiaotong-Liverpool University 0000-0002-2288-5116 Cheng-Hung Lo
Xi’an Jiaotong-Liverpool University 0000-0002-7199-9339 Hai-Ning Liang
Xi’an Jiaotong-Liverpool University Corresponding author (e-mail:
<EMAIL_ADDRESS>0000-0003-3600-8955

###### Abstract

Familiarity with audiences plays a significant role in shaping individual
performance and experience across various activities in everyday life. This
study delves into the impact of familiarity with non-playable character (NPC)
audiences on player performance and experience in virtual reality (VR)
exergames. By manipulating of NPC appearance (face and body shape) and voice
familiarity, we explored their effect on game performance, experience, and
exertion. The findings reveal that familiar NPC audiences have a positive
impact on performance, creating a more enjoyable gaming experience, and
leading players to perceive less exertion. Moreover, individuals with higher
levels of self-consciousness exhibit heightened sensitivity to the familiarity
with NPC audiences. Our results shed light on the role of familiar NPC
audiences in enhancing player experiences and provide insights for designing
more engaging and personalized VR exergame environments.

Human-centered computingHuman computer interaction (HCI)Interaction
paradigmsVirtual reality; Software and its engineeringSoftware organization
and propertiesVirtual worlds softwareInteractive games

Introduction

Virtual Reality (VR) exergames have gained significant popularity as an
innovative approach that combines physical exercise with immersive gaming
experiences [43, 45]. As sedentary lifestyles have become increasingly
prevalent, with prolonged sitting leading to various health concerns, VR
exergames offer a promising solution by promoting physical movement and
mitigating the negative effects associated with excessive sitting [51]. These
interactive virtual environments allow users to engage in physical activities
while being transported to fun and captivating virtual worlds [44, 46].

Non-Player Characters (NPC) and their feedback have been used in games to
enhance gameplay experiences [16, 50]. However, there is little research on
the mechanisms for establishing meaningful connections between these audiences
and players, particularly in VR exergames. Tice et al. [38] argued that how
individuals present themselves is influenced by their audience; specifically,
individuals may behave differently when facing familiar and unfamiliar
audiences [40, 27]. Furthermore, several studies [32, 6] have supported the
positive influence of familiar audiences on individual performance, as
encountering familiar individuals has been shown to evoke a sense of
connection, comfort, and heightened engagement. Conversely, encountering
unfamiliar individuals may elicit heightened nervousness or anxiety, but
sometimes it can also stimulate individuals to have a stronger desire to
perform and excel [22]. Research suggests that the extent of an audience’s
influence on users depends on an individual’s level of self-consciousness [2,
7, 39]. Individuals with high self-consciousness are more concerned about
others’ judgments and experience increased anxiety when being observed, which
can affect their performance and emotions.

A familiar audience has been shown to enhance social presence and increase
user motivation and enjoyment in various contexts, including virtual
environments. For instance, recent studies [25, 1] have demonstrated that when
delivering a speech in a VR environment and facing familiar audiences, users
tend to experience a greater sense of relaxation and exhibit improved
performance. However, the impact of audience familiarity on player experiences
in gaming contexts remains relatively unexplored.

Moreover, the role of voice familiarity has been largely overlooked. Notably,
audience familiarity can be perceived through different patterns of signals
originating not only from facial features but also from voices [49]. Familiar
appearances and voices can convey identity information and are believed to
create impressions of warmth, competence, and other social characteristics
[10, 34]. Understanding the influence of audience familiarity in VR exergames
is essential for creating engaging and personalized experiences. Therefore,
the primary objective of this work is to explore how familiarity with NPC
audiences, encompassing both appearance (facial features and body shape) and
voice, impacts players’ performance, experience, and exertion within the
context of VR exergames. Specifically, we seek to answer the following
research questions:

  * RQ1:

How would the familiar/unfamiliar appearances of NPC audiences affect players’
performance, experience, and exertion in VR exergames?

  * RQ2:

How would the familiar/unfamiliar voices of NPC audiences impact players’
performance, experience, and exertion in VR exergames?

  * RQ3:

How does the level of self-consciousness relate to the impact of audience
familiarity on players’ performance, experience, and exertion in VR exergames?

To answer these RQs, we conducted a 2 $\times$ 2 within-subjects experiment
(1. Audience Appearance—unfamiliar and familiar and 2. Audience
Voice—unfamiliar and familiar) with 24 young adults participating in a VR
exergame. Our findings point to the positive impact of both familiar audience
appearance and voice on players’ overall gaming experience, emotional state,
and perceived exertion. Furthermore, the familiar voice enhances player
performance in the game. Additionally, individuals with higher levels of self-
consciousness demonstrate a heightened sensitivity to the familiarity with NPC
audiences, leading to a greater sense of relaxation when facing familiar
audiences. We provide two design recommendations incorporating audience
familiarity to support designers and developers in shaping players’ game
performance and experience, ultimately contributing to a healthier lifestyle.

##  1 Related work

###  1.1 NPC Audience and Its Impact on Users

NPC audiences can have a great impact on users’ performance and experience.
For instance, Pertaub et al. [29] found that negative virtual audiences
triggered heightened anxiety levels among users during public speaking, in
contrast to positive and neutral audiences. Yakura and Goto [48] discovered
that when users are part of the concert audience, the behavior of other
concert NPC audiencs could significantly enhance their sense of co-presence
and improve their overall concert experience. Strojny et al. [36] studied VR
training for firefighter first response and found that social presence plays a
crucial role in moderating the impact of virtual audiences on performance in
such scenarios. Kabeko et al. [19] found NPCs’ feedback can enhance the user’s
experience and create a sense of “unity” with the audiences in a VR live
house. Raimbaud et al. [30] investigated the gaze behavior of virtual
audiences in VR, revealing that participants demonstrated quicker detection
and prolonged gaze duration in response to directed gaze, mirroring real-world
tendencies.

Prior research has also explored the influence of NPC audiences on video
games. For example, Haller et al. [16] suggested that feedback from a virtual
audience could lead to better performance and higher heart rates in players.
Xu et al. [47] found that the group size of an NPC audience and its feedback
could positively affect a player’s performance and experience while playing VR
exergames. Focusing on older players, Yu et al. [50] found that virtual
audiences with reactive feedback could enhance their performance and
experience in VR exergames. Yet, no studies have focused on the investigation
of audience familiarity specifically in the context of VR games, including VR
exergame. This work fills this gap.

###  1.2 Users’ Sense of Familiarity and Its Impact

From a psychological standpoint, familiarity can be defined as the level of
knowledge or acquaintance that an individual possesses regarding specific
stimuli, such as physical stimuli, environmental elements, and other
individuals [15]. For other individuals, familiarity can be perceived on a
continuum, ranging from complete strangers, and acquaintances, to close
friends and family.

Existing research has demonstrated a link between sensory familiarity and the
experience of positive affect [17, 13, 14]. For visual stimuli, Harmon-Jones
and Allen [17] found that participants exhibited greater activity in facial
muscles associated with positive affect after being exposed to familiar photos
than unfamiliar photos. Garcia-Marques et al. [13] demonstrated that
familiarity and positive affect influence each other’s judgment latencies
through a symbol judgment task. In the realm of auditory stimuli, Garcia-
Marques et al. [14] delved into the evaluation of recorded statements and
unveiled that the processing of familiar stimuli resulted in a pleasurable
subjective experience.

When confronted with stimuli beyond simple sensory input, such as familiar
people, individuals can also demonstrate more positive performance and
psychological states. For example, MacIntyre and Thivierge [23] found that in
public speaking, facing familiar audiences can make participants perceive
stronger agreeableness and willingness to speak and lower anticipated anxiety
than unfamiliar audiences. Burkitt et al. [6] investigated the effect of
audience familiarity on children’s expressive drawings of themselves and found
that children showed more positive expressiveness when faced with familiar
peers and adult audiences. Monteiro et al. [25] investigated the influence of
audience familiarity in a VR public speaking training tool and found that
participants with medium public speaking anxiety exhibited a significantly
more relaxed demeanor when faced with familiar NPC audiences.

These studies provide evidence that familiar audiences have the potential to
induce a more relaxed mood and facilitate participants’ performance. However,
there is currently limited research that incorporates the familiarity with the
NPC audiences within virtual gaming environments. Furthermore, our
understanding of the influence of visual and auditory stimuli presented by
audiences remains incomplete. To address these gaps, this study aims to
investigate how familiarity with the NPC audience’s appearance (including face
and body shape) and voice influence players’ performance and overall
experience in VR exergames.

###  1.3 Self-consciousness

While the presence of an audience is often believed to enhance individual
performance, it is essential to consider the role of self-consciousness, as it
can significantly impact how individuals respond to audience interactions [3].
Self-consciousness refers to an individual’s awareness and attention to their
own thoughts, feelings, and behaviors in relation to others [12]. It involves
a focus on how one is perceived by others and a concern for social evaluation.

Several studies [2, 7, 39] have explored the relationship between self-
consciousness and the influence of audiences on personal performance. For
example, Wang et al. [39] suggested that individuals with high levels of self-
consciousness may experience heightened anxiety and decreased performance in
front of an audience. This effect appears to be more pronounced when
individuals are confronting unfamiliar audiences. Mesagno et al. [24] observed
that basketball players with high self-consciousness showed significantly
increased anxiety and diminished performance when facing unfamiliar audiences.
In these instances, the presence of an audience may lead to self-doubt and
increased self-monitoring, which can disrupt performance and hinder task
execution [2]. Existing research [20, 16, 50] on audience familiarity in
virtual environments has paid limited attention to users’ self-consciousness.
Considering that self-consciousness may be a crucial influencing factor, we
aim to explore the relationship between players’ self-consciousness and their
exposure to NPC audience familiarity in this work.

##  2 Exergame Application

We have developed a VR exergame, which is inspired by Fruit Ninja, using the
Unity3D engine. Expanding on the base game, our design includes a fog
interference feature, encouraging players to squat and clear the fog, boosting
exertion, and adding a challenging aspect. Furthermore, our game includes
virtual audiences to enrich the player experience. All variables reported in
this section were decided through several playtesting sessions with four game
testers.

Figure 1: (a) Real and (b) Virtual perspectives of fruit slicing gameplay
using controllers. (c) Real and (d) Virtual perspectives of squatting to clear
fog interference.

###  2.1 Rules and Logic

During the game, players are required to use two hand-held controllers to
wield virtual swords to slice as many fruits (watermelon, apple, and lemon) as
possible and dodge bombs. Figure 1 shows that fruits and bombs are launched
towards the left and right sides of the player, following a parabolic
trajectory that enables them to land within the reachable area of the player’s
virtual sword. To ensure trajectory reliability, we first adjusted the gravity
setting based on feedback from the four game testers of different heights
(160cm - 185cm), thereby extending the flight time of the targets. We also
adjusted the initial velocities on the X, Y, and Z axes to restrict the angle
range, allowing participants to hit the targets within a consistent area of
approximately one square meter.

The game lasts 5 minutes and 12 seconds, composed of 5 one-minute game
sequences with 3 seconds of rest time between each game sequence. Each one-
minute sequence consists of 20 3-second rounds that generate a fixed number of
fruits and bombs in random order. Each round contains 2-4 fruits, with a bomb
appearing every 4-5 rounds. In total, there are 100 rounds (20 per minute),
and the occurrences of each target are as follows: (1) watermelon: 90, (2)
apple: 80, (3) lemon: 85, and (4) bomb: 20.

The game also includes a fog interference feature which obstructs the player’s
view to elevate the challenge and variation of the gameplay. The player needs
to squat to disperse the fog and regain their vision (Figure 1). We utilized
the Steam effects from Unity’s Particle pack to create the fog, with a
simulation speed of 1 and a resulting shape approximating a sphere with a
diameter of 1.8 meters. We placed four white-gray smoke effects around the
camera to completely obstruct the player’s view. The fog generation frequency
was set at 6-10 seconds, resulting in the appearance of fog approximately
25-35 times per game, based on the player’s 3-second reaction and squatting
duration. This ensured the fog interference mechanism was sufficiently
challenging without compromising the players’ overall gaming experience.

###  2.2 Audience Setting

To ensure optimal visibility of each NPC audience’s faces, we positioned four
NPCs as audiences in the player’s field of view. These NPCs provided both
positive and negative feedback to the player, with each feedback consisting of
two different animations and two voice lines (Figure 2). The two positive
feedback animations include raising both hands and jumping while waving one
hand upward when cheering for the player. The two negative feedback animations
consist of covering the face with both hands and lowering the head while
waving one hand downward. The positive voice lines are delivered with
excitement and joy, while the negative voice lines convey a sense of
disappointment and frustration. To enable participants to identify the voices
of the NPCs, their voice feedback was set to first emit some exclamations
(such as “Oh” and “Wow”) together, and then a random audience member played a
voice line with content (such as “Great job” and “What a pity”). The four NPCs
provided feedback simultaneously, but the specific animations and voice lines
played are randomized to prevent predictability.

Figure 2: Top Row: (a) Unfamiliar NPC audiences, (b) Unfamiliar NPC audiences
providing positive feedback, (c) Unfamiliar NPC audiences expressing negative
feedback. Bottom Row: (d) Familiar NPC audiences, (e) Familiar NPC audiences
providing positive feedback, (f) Familiar NPC audiences expressing negative
feedback.

###  2.3 Scoring System And Feedback Activation

As shown in Table 1, players received three types of scores: total score,
combo count, and rating score. The total score shows on the upper right corner
of the gameplay screen and reflects the total points gained at the end of the
gameplay. Combo count tracked the consecutive number of sliced fruits, which
is presented below the total score display. The rating score with rating level
served as a trigger for NPC feedback and was not visible to players. The
rating score and rating level both start at 0. Each level is separated by a
10-point interval, which is determined by dividing the current rating score by
10 and taking the integer part. When players reach a higher level, it triggers
positive feedback, while descending to a lower level triggers negative
feedback. There is no upper limit to the rating level, but the lower limit is
set at 0. If a player remains at level 0 for over 6 seconds, it also triggers
negative feedback. To prevent excessive disruptions, a 4.5-second cooldown
period followed each feedback event, during which no additional feedback was
triggered.

Table 1: Scoring Metrics for Fruits and Bombs - Total Score, Combo Count, and
Rating Score

Item | State | Total Score | Combo Count | Rating Score
---|---|---|---|---
Watermelon | Sliced | +3 | +1 | +5
| Missed | -7 | Reset to 0 | -5
Apple | Sliced | +5 | +1 | +5
| Missed | -5 | Reset to 0 | -5
Lemon | Sliced | +7 | +1 | +5
| Missed | -3 | Reset to 0 | -5
Bomb | Hit | -10 | Reset to 0 | -10

##  3 Experiment

###  3.1 Experiment Design

The study employed a 2 $\times$ 2 within-subjects design that incorporated two
factors: Audience Appearance (unfamiliar and familiar) and Audience Voice
(unfamiliar and familiar). In total, we have evaluated 4 conditions: (1)
Unfamiliar Appearance with Unfamiliar Voice (UAUV), (2) Unfamiliar Appearance
with Familiar Voice (UAFV), (3) Familiar Appearance with Unfamiliar Voice
(FAUV), and (4) Familiar Appearance with Familiar Voice (FAFV). The order of
these conditions was counterbalanced in the experiment.

When creating familiar audiences, the familiar face was obtained via scanned
photographs of participants’ friends (using the Avatar Maker Pro plugin), and
the body shape and height were generated by adjusting the size of the models.
The same individuals also provided familiar voices through voice recordings.
On the other hand, the unfamiliar audiences were created using realistic
computer character models, and the unfamiliar voices were generated by
Microsoft Azure, an AI voice generator that produces natural and smooth human
speech based on text. Other factors such as the phrases used for the voices,
physical characteristics of the NPC audiences (adjusted to suit the
individuals known to the player), and the number of NPCs were controlled in
all conditions.

###  3.2 Outcome Measures

  * •

_Player Performance._ We collected the following performance measurements: (1)
game score; (2) success rate of fruit hit and avoiding bomb; (3) count of
positive and negative feedback; and (4) maximum combo count. See Section 3 for
a detailed description.

  * •

_Player Experience._ We employed the following three scales:

    * –

Player Experience of Need Satisfaction (PENS) scale [33]: a 21-item scale
designed to measure game experience across five dimensions. (1) Competence:
the players’ perception of their own capabilities. (2) Autonomy: the extent to
which players felt free to make choices within the game. (3) Relatedness: the
players’ sense of connection to ”other players in the game,” (i.e., the NPC
audience in our study). (4) Presence/Immersion: players’ emotional engagement
in the game. (5) Intuitive Controls: the degree to which players feel that
their choices translate smoothly and seamlessly into in-game actions.

    * –

Pick-A-Mood (PAM) tool [9]: a cartoon-based pictorial instrument for quick and
intuitive reporting and expression of mood states. This tool categorized eight
distinct mood states into four main categories: Energized-Pleasant (excited
and cheerful), Calm-Pleasant (relaxed and calm), Energized-Unpleasant
(irritated and tense), and Calm-Unpleasant (bored and sad).

    * –

Simulator Sickness Questionnaire (SSQ) [21]: a commonly used 16-item self-
report questionnaire that produces 3 measures of cybersickness (nausea,
oculomotor, and disorientation). A total SSQ score ranging from 20 to 30
indicates mild to moderate simulator sickness, while a score exceeding 40 is
indicative of a poor simulator experience [8].

  * •

_Exertion._ The exertion was assessed by (1) the average heart rate (AvgHR%)
using the formula the average heart rate / the participant’s estimated maximum
heart rate (i.e., 211-0.64×age [26]); (2) calories burned; and (3) the Borg
Rating of Perceived Exertion (RPE) 6-20 scale [4].

  * •

_Self-Consciousness Scale (SCS)._ The SCS [12] consisted of three subscales
(private self-consciousness, public self-consciousness, and social anxiety),
and the scores from the three subscales are summed to obtain an individual’s
total self-consciousness score. Private self-consciousness refers to an
individual’s tendency to introspect and reflect on their inner thoughts,
feelings, and experiences. Public self-consciousness, on the other hand,
refers to an individual’s awareness of how they are perceived by others in
social situations. Social anxiety is the tendency to experience discomfort and
anxiety in social situations.

  * •

_Ranking and Interviews._ We asked participants to rank the evaluated
conditions and provide reasons for their rankings. Then, we employed a semi-
structured interview with the following open-ended questions: (1) “How do you
think the NPCs’ familiarity affects your overall performance of the game?”;
(2) “How do you think the NPCs’ familiarity affects your overall game
experience?”; (3) “Which factor of the NPCs do you think has a greater impact
on your game experience, the appearance or the voice?”; (4) “How do you think
positive and negative feedback from the NPCs affect you?”; and (5) “Would
having familiar NPCs in future VR exergames encourage you to continue playing
in the long term?”. Interviews were recorded and transcribed for data
analysis.

###  3.3 Participants

We recruited 24 participants (8 females; mean age = 23.00, SD = 2.02, range =
20 to 28) through an on-campus social media platform. Out of the 18
participants who reported having prior experience with VR HMDs, 9 were
frequent weekly users. 11 of them had played exergames before, but none were
regular players. Regarding how engaged they were with daily exercise, 5
participants exercised regularly (more than 3 hours per week), 13 participants
were less regular (1-3 hours per week), and 6 were inactive (less than 1 hour
per week).

###  3.4 Apparatus and Setup

The experiment used a Meta/Oculus Quest 2 as the VR device and a Polar OH1 for
monitoring participants’ HR and calories burned. The experiment was conducted
in a controlled laboratory environment that was well-illuminated and isolated
from external disturbances. The room temperature was regulated by an air
conditioner that maintained a constant temperature of 24℃ during the
experiment. The experiment was conducted under close supervision by an
experimenter to prevent any potential risks. This experiment received approval
from the University Ethics Committee at the host institution.

Figure 3: Mean total score, fruit cut rate, bomb avoidance rate, positive
feedback count, negative feedback count, and maximum combo count for each
condition. Error bars indicate 95% confidence intervals.

###  3.5 Procedures

Participants were provided with a comprehensive introduction of the
experimental protocol to read and a consent form to sign off prior to
participating in the study. Then, they were required to bring 4 friends in a
separate appearance and voice collection session to generate NPC before the
experiment. Their friends would also need to sign the consent form to agree
that they were willing to form the NPCs in the game. During the appearance and
voice collection session, participants’ friends were instructed (1) to
maintain a neutral expression and to fully exhibit their facial features to
generate the best facial expression, (2) to provide verbal feedback based on a
list of prompts, which consisted of both exclamations (such as “Oh” and “Wow”)
and complete sentences (such as “Great job”, “Well done”, “Oh no”, and “What a
pity”) [11]. All photographs and voice recordings were collected using an
iPhone 11. After creating the familiar NPCs, participants were asked to
independently identify the models and voices of the NPCs to ensure their
recognizability. No difficulties were reported during this process.

On the day of the experiment, participants needed to complete a pre-experiment
questionnaire asking demographic questions including age, gender, frequency of
exercise, experience with exergames and VR HMDs, as well as self-consciousness
via SCS. Then, participants were required to enter their personal information
(i.e., age, gender, height, and weight) into the Polar Beat mobile
application. We collected the rest level HR using the Polar OH1 HR monitor by
asking participants to relax and sit still for over 1 minute.

Before the formal gameplay sessions, a 3-minute training phase without any
NPCs was administered to enable participants to practice moves and become more
acquainted with the equipment. For each experimental condition, participants
were assisted by the experimenter to wear the Polar OH1 and HMD. The
experiment commenced only when the participant’s heart rate had reached the
resting level. After each condition, participants needed to complete four
questionnaires: PENS [33], PAM [9], SSQ [21], and Borg RPE 6-20 [4]. They then
rested until they felt ready to begin the next experimental condition and had
reached a resting heart rate level. At the end of the experiment, participants
underwent a semi-structured interview to rank the experimental conditions and
provide feedback on their experiences. The experiment lasted about 50 minutes
for each participant.

##  4 Results

We conducted statistical analysis on the data using a two-way repeated
measures ANOVA with Audience Appearance (unfamiliar and familiar) and Audience
Voice (unfamiliar and familiar) as within-subjects variables. The normal
distribution of the data was assessed using Shapiro-Wilks tests and Q-Q plots.
For non-normally distributed data, we applied the Aligned Rank Transform (ART)
to transform the data before performing repeated-measures ANOVAs. We utilized
Bonferroni correction for pairwise comparisons, and we reported effect sizes
whenever feasible ($\eta_{p}^{2}$).

To analyze correlations between the participants’ self-consciousness and their
performance and experience, we conducted Pearson’s bivariate correlation
analyses.

Figure 4: PEN and PAM ratings for each condition. Error bars indicate 95%
confidence intervals.

###  4.1 Player Performance

Figure 3 shows the performance measures for each condition. ANOVA tests
yielded a significant main effect of Audience Voice on total score
($F_{1,23}=6.843,p=.015,\eta_{p}^{2}=0.229$), but not for Audience Appearance
($F_{1,23}=0.437,p=.515$) and their interaction effect
($F_{1,23}=0.209,p=.652$). Pairwise comparisons revealed that participants
achieved higher scores when exposed to a familiar audience voice
($M=876.29,SE=40.50$) than unfamiliar audience voice ($M=847.21,SE=44.94$).

For fruit cut rate, there was a significant main effect of Audience Voice
($F_{1,23}=5.691,p=.026,\eta_{p}^{2}=0.198$), but no significant effects were
observed for Audience Appearance ($F_{1,23}=0.346,p=.562$) and Audience
Appearance $\times$ Audience Voice ($F_{1,23}=0.825,p=.373$). Subsequent
pairwise comparisons revealed that participants exhibited a higher fruit cut
rate when exposed to familiar audience voice ($M=86\%,SE=0.02$) in comparison
to unfamiliar audience voice ($M=85\%,SE=0.02$).

The data of maximum combo count was not normally distributed and underwent an
ART prior to conducting the RM-ANOVA. Our analysis suggested Audience Voice
($F_{1,23}=8.214,p=.009,\eta_{p}^{2}=0.263$) had a significant effect on
player’s maximum combo count, but not Audience Appearance
($F_{1,23}=1.849,p=.187$) and Audience Appearance $\times$ Audience Voice
($F_{1,23}=1.047,p=.317$). Post-hoc pairwise comparisons revealed that
participants achieved a significantly higher maximum combo count in familiar
voice conditions ($M=30.27,SE=2.63$) than in unfamiliar voice conditions
($M=27.52,SE=2.68$). No significant effects were found for bomb avoidance
rate, positive feedback count, and negative feedback count.

Pearson’s correlation unveiled a significant correlation between participants’
self-consciousness and (1) the number of negative feedback they triggered when
facing an unfamiliar audience appearance ($r=-.437,p=.033$); (2) their maximum
combo count when confronted with a familiar audience appearance
($r=.414,p=.044$) and (3) familiar audience voice ($r=.422,p=.040$). No other
significant correlations were found.

###  4.2 Player Experience

####  4.2.1 Game Experience

Values for each condition for PENS ratings can be found in Figure 4.
Concerning Competence, ANOVA analysis revealed significant main effects for
Audience Appearance ($F_{1,23}=13.327,p=.001,\eta_{p}^{2}=0.367$) and Audience
Voice ($F_{1,23}=14.266,p=.001,\eta_{p}^{2}=0.383$), while no significant
interaction effect was found ($F_{1,23}=0.268,p=.610$). Participants reported
a heightened sense of competence when (1) presented with a familiar audience
appearance ($M=5.58,SE=0.16$) in contrast to an unfamiliar appearance
($M=4.92,SE=0.24$), (2) exposed to a familiar audience voice
($M=5.46,SE=0.18$) compared to unfamiliar voices ($M=5.04,SE=0.20$).

Our analysis found significant main effects of Audience Appearance
($F_{1,23}=22.255,p=.000,\eta_{p}^{2}=0.492$) and Audience Voice
($F_{1,23}=21.203,p=.000,\eta_{p}^{2}=0.480$) on Autonomy. No significant
interaction effect of these two factors was found ($F_{1,23}=1.184,p=.288$).
Participants expressed a stronger sense of autonomy (1) when facing a familiar
audience appearance ($M=5.43,SE=0.15$) than an unfamiliar appearance
($M=4.69,SE=0.20$) and (2) when exposed to a familiar audience voice
($M=5.43,SE=0.15$) compared to unfamiliar voice ($M=4.69,SE=0.19$).

ANOVA tests indicated significant main effects of Audience Appearance
($F_{1,23}=50.013,p=.000,\eta_{p}^{2}=0.685$) and Audience Voice
($F_{1,23}=45.091,p=.000,\eta_{p}^{2}=0.662$) on Relatedness. No significant
interaction effect was observed for Audience Appearance $\times$ Audience
Voice ($F_{1,23}=0.003,p=.957$). Participants reported a stronger sense of
relatedness (1) when encountering familiar audience appearance
($M=4.88,SE=0.18$) compared to unfamiliar appearance ($M=3.63,SE=0.19$) and
(2) when exposed to familiar audience voice ($M=4.83,SE=0.19$) compared to
unfamiliar voice ($M=3.68,SE=0.18$).

For Presence/Immersion, significant main effects were found for Audience
Appearance ($F_{1,23}=16.152,p=.001,\eta_{p}^{2}=0.413$) and Audience Voice
($F_{1,23}=16.565,p=.000,\eta_{p}^{2}=0.419$), but not for Audience Appearance
$\times$ Audience Voice ($F_{1,23}=3.871,p=.061$). Participants experienced a
higher level of immersion (1) with a familiar audience appearance
($M=5.06,SE=0.16$) in contrast to an unfamiliar appearance ($M=4.64,SE=0.17$)
and (2) when presented with a familiar audience voice ($M=5.00,SE=0.16$)
compared to unfamiliar voice ($M=4.70,SE=0.17$). Notably, no main nor
interaction effects were found for Intuitive Controls.

Furthermore, Pearson’s correlation revealed significant associations between
participants’ self-consciousness and their perceived Competence when faced
with a familiar audience appearance ($r=.431,p=.036$) and familiar audience
voice ($r=.424,p=.039$). Additionally, we found a significant correlation
between participants’ self-consciousness and their perceived Relatedness when
exposed to familiar audience appearance ($r=.494,p=.014$) and familiar
audience voice ($r=.460,p=.024$). No other significant correlations were
observed.

####  4.2.2 Emotion

The ratings for PAM in each condition can be observed in Figure 4. Regarding
Energized-Pleasant, Our analysis showed a significant main effect of Audience
Voice ($F_{1,23}=19.959,p=.000,\eta_{p}^{2}=0.465$), but not for Audience
Appearance ($F_{1,23}=3.119,p=.091$) and interaction effects
($F_{1,23}=0.371,p=.548$). Participants reported a heightened sense of
energized-pleasantness when exposed to a familiar audience voice
($M=5.28,SE=0.22$) as opposed to an unfamiliar audience voice
($M=4.49,SE=0.25$).

In terms of Energized-Unpleasant, ANOVA tests revealed a significant main
effect of Audience Appearance ($F_{1,23}=9.543,p=.005,\eta_{p}^{2}=0.293$),
but not for Audience Voice ($F_{1,23}=0.466,p=.502$) and interaction effects
($F_{1,23}=3.363,p=.080$). Participants expressed a stronger sense of
energized-unpleasantness when confronted with an unfamiliar audience voice
($M=2.75,SE=0.21$) than a familiar audience voice ($M=2.85,SE=0.27$).

For Calm-Unpleasant, ANOVA tests yielded a significant main effect of Audience
Appearance ($F_{1,23}=9.425,p=.005,\eta_{p}^{2}=0.291$), but not for Audience
Voice ($F_{1,23}=3.955,p=.059$) and Audience Appearance $\times$ Audience
voice ($F_{1,23}=0.070,p=.793$). Participants reported a greater degree of
calm-unpleasantness when exposed to an unfamiliar audience voice
($M=3.05,SE=0.26$) compared to a familiar audience voice ($M=2.77,SE=0.28$).

No significant effects were observed for the Calm-Pleasant category. Moreover,
our analysis did not reveal any significant correlations between the four
emotional categories and participants’ self-consciousness.

####  4.2.3 Simulator Sickness

None of our participants had an SSQ higher than 20 among four conditions—UAUV
($M=3.27,SE=3.87$), UAFV ($M=2.81,SE=4.01$), FAUV ($M=2.96,SE=4.41$), and FAFV
($M=2.96,SE=4.41$). Our analysis also did not show significant results on
Nausea, Oculomotor, Disorientation, as well as total SSQ scores.

Figure 5: AvgHR%, Calories burned, and Borg ratings for each condition. Error
bars indicate 95% confidence intervals.

###  4.3 Exertion

Values for each condition for exertion measures can be found in Figure 5.
ANOVA tests revealed significant main effects of Audience Appearance
($F_{1,23}=5.374,p=.030,\eta_{p}^{2}=0.189$) and Audience Voice
($F_{1,23}=5.979,p=.015,\eta_{p}^{2}=0.231$) on perceived exertion (Borg RPE;
after data were transformed via ART). No significant interaction effects were
found ($F_{1,23}=0.702,p=.411$). Post-hoc pairwise comparisons indicated that
participants experienced a higher level of exertion when (1) exposed to
unfamiliar audience appearance ($M=6.02,SE=0.59$) compared to familiar
audience appearance ($M=5.34,SE=0.59$)(2) confronted with unfamiliar audience
voice ($M=5.98,SE=0.60$) than familiar audience voice ($M=5.44,SE=0.57$). We
did not observe any significant main or interaction effects on avgHR% and
calories burned.

Pearson’s correlation revealed a significant correlation between participants’
self-consciousness and their avgHR% when exposed to unfamiliar audience
appearance ($r=.428,p=.037$) and unfamiliar audience voice ($r=.459,p=.024$).

###  4.4 User Rankings and Feedback

Out of the 24 participants, 21 ranked Familiar Appearance with Familiar Voice
(FAFV) as the best condition while the remaining 3 participants chose each of
the other three conditions respectively. For the second place, 14 participants
ranked Unfamiliar Appearance with Familiar Voice (UAFV) as their second
choice, while 7 participants ranked Familiar Appearance with Unfamiliar Voice
(FAUV) as their second choice. When asked about which factor (appearance or
voice) had a more significant effect, 17 participants indicated that they were
more easily influenced by audience voice, particularly when they were exposed
to familiar audience voice.

When queried about additional details pertaining to their gaming experiences,
17 participants (P1-5, P11-P17, P19, P21-24) expressed a proclivity towards
familiar elements, perceiving games featuring these elements as more
_“enjoyable/interesting”_. 7 participants (P3-P5, P8, P10, P16, P22) conveyed
that the presence of familiar elements instilled a sense of
_“comfort/companionship”_ during gameplay. Moreover, 4 participants (P9, P15,
P19-P20) reported feeling _“relaxed”_ when confronted with familiar elements.
Notably, a subset of 14 participants (P4-P6, P8-P10, P12-P13, P15, P18-P19,
P21, P23-P24) opined that familiar elements fostered _“focus”_ and _“enhanced
performance,”_ albeit 4 participants (P1, P3, P11, P22) perceived such
elements as _“distracting”_ and impeding their gaming experience.

There was a mixed attitude towards positive and negative feedback, 7
participants (P1-P2, P5, P7, P9, P14, P17) perceived positive feedback as
having a positive impact, whereas negative feedback was regarded as having a
negative impact. In contrast, 6 participants (P3-P4, P13, P15-P16, P23)
recognized both types of feedback being positive and identified negative
feedback as a stimulus for _“competitiveness”_. 6 participants (P6, P8, P10,
P12, P18, P21) affirmed that both positive and negative feedback from familiar
audience served as _“motivation,”_ whereas feedback from unfamiliar sources
elicited no impact.

Regarding the potential of familiar audiences in future VR exergames to
promote long-term engagement, 19 participants expressed a positive outlook.
They conveyed a desire for NPC audiences that could be _“customized”_ and
demonstrate heightened _“intelligence.”_ However, the remaining 5 participants
(P7, P13-P14, P17, P22) who responded negatively held the view that the sense
of _“comfort”_ and _“novelty”_ elicited by familiar audiences was only
ephemeral.

##  5 Discussion

###  5.1 Impact of Appearance Familiarity on Player Performance and Experience

To address RQ1, our research findings indicate that while appearance
familiarity does not significantly impact player performance, it does
demonstrate effects in enhancing player experience, promoting positive
emotions, and reducing perceived exertion levels. This aligns with prior
research findings [23], which indicate that individuals tend to feel more
relaxed and pleasant and have enhanced experiences when facing familiar
audiences. These positive effects can be attributed to the familiarity and
social connection established between the individuals and the audience,
creating a more comfortable and engaging atmosphere [6].

However, while previous studies [25, 1] have shown the influence of appearance
familiarity with the audience on performance outcomes in VR speech training
tools, our findings did not reveal a significant effect in the context of
exergames. One possible explanation for this discrepancy is the nature of the
visually dominant gameplay, which requires players to maintain a visual focus
on the tasks at hand. Several participants (P2, P4, P7, P16) mentioned that at
the start of the game, they would purposefully gaze at the NPC’s faces, but as
the game progressed, they would focus on the gameplay itself with occasional
glances towards them. It is worth noting that individuals have limited
attentional capacity [18], and they may not have enough available cognitive
resources to allocate to the appearance aspects of NPC audiences.

###  5.2 Impact of Voice Familiarity on Player Performance and Experience

Regarding RQ2, we found that voice familiarity played a crucial role in
enhancing both gameplay performance and subjective experiences. Participants
demonstrated notable improvements in their total score, fruit cut rate, and
maximum combo count when exposed to familiar voices of NPC audiences. Similar
to the appearance aspect, familiar voices also have a positive impact on
player experience, emotions, and perceived level of exertion.

One possible reason for the influence of voice familiarity on both performance
and experience can be attributed to the characteristics of audio stimuli.
Audios are typically provided for shorter durations than visuals, enabling
immediate and continuous auditory cues that offer a constant stream of
feedback throughout the interaction [41]. Moreover, audios are emitted
omnidirectionally and constantly, as our ears cannot be closed, ensuring
effective feedback delivery regardless of user orientation or visual focus
[35]. Voice feedback does not occupy valuable visual space, allowing users to
fully utilize their visual attention for other important aspects of the
interaction [28, 5]. While previous research [25, 1, 31] on audience
familiarity in virtual environments has rarely involved voice familiarity, our
findings indicate that the presence of familiar audience voice can have a
meaningful impact on both the performance and overall engagement of users in
VR exergames.

###  5.3 Relationship between Self-Consciousness and the Impact of Audience
Familiarity

To answer RQ3, while there was a limited association between users’ self-
consciousness and audience familiarity in terms of performance, there was a
significant correlation in terms of experience and average heart rates. Our
results indicate that the presence of NPCs does not appear to impose pressure
on participants with higher levels of self-consciousness, nor does it
significantly impact their performance. However, the inclusion of familiar
NPCs enhances their subjective experience and contributes to a more relaxed
feeling. Interestingly, in the presence of unfamiliar audience stimuli,
participants with higher self-consciousness levels may experience increased
physiological responses, as reflected by elevated heart rates. On the other
hand, they felt a greater sense of relatedness and competence when interacting
with familiar audiences. The presence of familiar audiences seemed to provide
them with a sense of comfort and social support.

The results showed that participants with higher levels of self-consciousness
demonstrated a greater sensitivity to the perception of audience familiarity,
both in terms of appearance and voices. This finding aligns with previous
research [39, 37] that suggests individuals with higher self-consciousness are
more attentive to social cues and the perception of others’ judgments.
Previous research [20, 16, 50] has shown that the presence and feedback of an
audience can enhance player performance and experience with limited
exploration of players’ self-consciousness. Our findings indicate that for
individuals with self-conscious tendencies, the presence of familiar audiences
may have a positive influence, resulting in a more relaxed and enjoyable
gaming experience.

###  5.4 Design Guidelines

####  5.4.1 Incorporating Audience Familiarity into Exergames

One of the key findings of our study is the positive impact of incorporating
audience familiarity into gameplay. By integrating familiar NPC audiences,
players not only improved performance but also enjoyed a heightened sense of
game experience and positive emotions. Notably, our findings shed light on the
influence of personality traits, particularly self-consciousness, on the
effects of audience interactions. Understanding the role of personalities in
audience interactions enables developers to tailor the game experience to
individual differences.

To facilitate familiarity, we recommend the inclusion of customizable features
(1. appearance—face, height, and body shape and 2. voice) for NPC audiences in
VR exergames. By allowing players to import and incorporate their own network
of acquaintances into the game, such as their friends and family members, NPC
avatars can resemble familiar individuals from their personal lives. This
recommendation acknowledges the significance of individual differences and
empowers players to enhance their enjoyment and immersion in VR exergames.

####  5.4.2 Prioritizing Voice Familiarity

We recommend prioritizing integrating familiar voices in the design of NPC
audiences in VR exergames. Voice familiarity played a pivotal role in
influencing player performance and experience in VR exergames, while
appearance familiarity only impacts experience. In addition, voice-only
familiarity has a higher rating than appearance-only familiarity based on the
ranking data and participants’ interview feedback. Most importantly, the key
advantage of emphasizing voice familiarity is the relative ease of capturing
and incorporating familiar voices compared to facial features. Voice
recordings can be obtained with greater convenience and accuracy, facilitating
seamless integration into the game. This accessibility empowers games to
easily leverage the power of familiar voice cues, enabling games with a more
personalized and engaged gameplay experience for players.

###  5.5 Limitations and Future Work

Our study has provided valuable insights into the impact of audience
familiarity on player performance and experience in VR exergames. However,
there are opportunities for further exploration and improvement that can build
upon our findings. One potential direction for future research is to expand
the range of variables considered beyond facial appearance and voice. In
particular, incorporating other elements, such as facial expressions and
clothing, can offer a more comprehensive understanding of how different
aspects of audience familiarity influence player experiences.

Another area of improvement lies in the feedback provided by the NPC audience.
While our study included a limited set of voice prompts and animations, there
is room to enhance the immersive experience by incorporating a broader range
of vocal expressions and animated responses. By allowing for customized vocal
expressions and animations, future research can enable more dynamic and
personalized interactions between players and the NPC audience.

The study participants mainly came from a young population. Exploring a wider
range of age groups and demographic characteristics in the future will enhance
the overall comprehensiveness of our findings. Furthermore, our study was
conducted as a short-term experiment, limiting our understanding of the long-
term effects of audience familiarity. Future research could address this
limitation by conducting longitudinal studies that examine the sustained
effects of audience familiarity over an extended period, such as a 6-week
experiment in [42]. This would provide valuable insights into how familiarity
with the virtual audience develops and evolves over time and how it impacts
player engagement and performance in the long run. Additionally, while our
results did not reveal significant issues with appearance and auditory
mismatches—as evidenced by participants’ ranking preferences—further
investigation into factors like player acceptance and familiarity perception
could be beneficial.

##  6 Conclusion

Our research illuminates the importance of audience familiarity in the context
of VR exergames. We have demonstrated that both appearance and voice
familiarity contributes to the player experience and perceived exertion, with
voice familiarity exerting a more prominent influence on player performance.
The positive impact of familiar NPC audiences on player experiences,
particularly in terms of creating a relaxed and enjoyable atmosphere, suggests
the potential for enhancing engagement and satisfaction in virtual reality
environments. Furthermore, we discovered that individuals with higher self-
consciousness are more sensitive to the influence of audience familiarity.
This underscores the importance of considering individual differences and
personal traits when designing virtual environments to ensure optimal player
engagement and comfort. By emphasizing the integration of appearance and voice
familiarity in NPC audience design, our study contributes to the advancement
of immersive VR exergames that cater to individual preferences and promote
positive player outcomes. Our findings offer valuable insights to developers,
designers, and researchers in creating engaging VR exergames that harness the
power of audience familiarity.

###### Acknowledgements.

The authors want to express gratitude to the participants who took part in the
study, as well as to the reviewers, for their valuable insights and
constructive suggestions that helped improve the paper.

## References

  * [1] A. Barrett, A. Pack, D. Monteiro, and H.-N. Liang.  Exploring the influence of audience familiarity on speaker anxiety and performance in virtual reality and real-life presentation contexts.  Behaviour & Information Technology, pp. 1–13, 2023.
  * [2] R. F. Baumeister.  Choking under pressure: self-consciousness and paradoxical effects of incentives on skillful performance.  Journal of personality and social psychology, 46(3):610, 1984.
  * [3] C. Belletier, A. Normand, and P. Huguet.  Social-facilitation-and-impairment effects: From motivation to cognition and the social brain.  Current Directions in Psychological Science, 28(3):260–265, 2019\.
  * [4] G. A. Borg.  Psychophysical bases of perceived exertion.  Medicine & science in sports & exercise, 1982.
  * [5] I. d. V. Bosman, O. . Buruk, K. Jørgensen, and J. Hamari.  The effect of audio on the experience in virtual reality: a scoping review.  Behaviour & Information Technology, pp. 1–35, 2023.
  * [6] E. Burkitt, D. Watling, and H. Message.  Expressivity in children’s drawings of themselves for adult audiences with varied authority and familiarity.  British Journal of Developmental Psychology, 37(3):354–368, 2019\.
  * [7] C. S. Carver and M. F. Scheier.  Self-focusing effects of dispositional self-consciousness, mirror presence, and audience presence.  Journal of personality and social psychology, 36(3):324, 1978.
  * [8] P. Caserman, A. Garcia-Agundez, A. Gámez Zerban, and S. Göbel.  Cybersickness in current-generation virtual reality head-mounted displays: systematic review and outlook.  Virtual Reality, 25(4):1153–1170, 2021.
  * [9] P. M. Desmet, M. H. Vastenburg, and N. Romero.  Mood measurement with pick-a-mood: review of current methods and design of a pictorial self-report scale.  Journal of Design Research, 14(3):241–279, 2016.
  * [10] H. D. Ellis, D. M. Jones, and N. Mosdell.  Intra-and inter-modal repetition priming of familiar faces and voices.  British Journal of Psychology, 88(1):143–156, 1997.
  * [11] L. K. Epting, K. N. Riggs, J. D. Knowles, and J. J. Hanky.  Cheers vs. jeers: Effects of audience feedback on individual athletic performance.  North American Journal of Psychology, 13(2), 2011.
  * [12] A. Fenigstein, M. F. Scheier, and A. H. Buss.  Public and private self-consciousness: Assessment and theory.  Journal of consulting and clinical psychology, 43(4):522, 1975.
  * [13] T. Garcia-Marques, D. M. Mackie, H. M. Claypool, and L. Garcia-Marques.  Is it familiar or positive? mutual facilitation of response latencies.  Social Cognition, 28(2):205–218, 2010.
  * [14] T. Garcia-Marques, M. Prada, and D. M. Mackie.  Familiarity increases subjective positive affect even in non-affective and non-evaluative contexts.  Motivation and Emotion, 40:638–645, 2016.
  * [15] P. S. Goodman and D. P. Leyden.  Familiarity and group productivity.  Journal of applied psychology, 76(4):578, 1991.
  * [16] J. C. Haller, Y. H. Jang, J. Haller, L. Shaw, and B. C. Wünsche.  Hiit the road: Using virtual spectator feedback in hiit-based exergaming.  In Proceedings of the Australasian Computer Science Week Multiconference, pp. 1–9, 2019.
  * [17] E. Harmon-Jones and J. J. Allen.  The role of affect in the mere exposure effect: Evidence from psychophysiological and individual differences approaches.  Personality and Social Psychology Bulletin, 27(7):889–898, 2001\.
  * [18] B. Hubert-Wallander, C. S. Green, and D. Bavelier.  Stretching the limits of visual attention: the case of action video games.  Wiley interdisciplinary reviews: cognitive science, 2(2):222–230, 2011.
  * [19] T. Kaneko, H. Tarumi, K. Kataoka, Y. Kubochi, D. Yamashita, T. Nakai, and R. Yamaguchi.  Supporting the sense of unity between remote audiences in vr-based remote live music support system ksa2.  In 2018 IEEE International Conference on Artificial Intelligence and Virtual Reality (AIVR), pp. 124–127. IEEE, 2018.
  * [20] D. L. Kappen, P. Mirza-Babaei, J. Johannsmeier, D. Buckstein, J. Robb, and L. E. Nacke.  Engaged by boos and cheers: the effect of co-located game audiences on social player experience.  In Proceedings of the first ACM SIGCHI annual symposium on Computer-human interaction in play, pp. 151–160, 2014.
  * [21] R. S. Kennedy, N. E. Lane, K. S. Berbaum, and M. G. Lilienthal.  Simulator sickness questionnaire: An enhanced method for quantifying simulator sickness.  The international journal of aviation psychology, 3(3):203–220, 1993.
  * [22] M. R. Leary, J. B. Nezlek, D. Downs, J. Radford-Davenport, J. Martin, and A. McMullen.  Self-presentation in everyday interactions: effects of target familiarity and gender composition.  Journal of personality and social psychology, 67(4):664, 1994.
  * [23] P. D. MacIntyre and K. A. Thivierge.  The effects of audience pleasantness, audience familiarity, and speaking contexts on public speaking anxiety and willingness to speak.  Communication Quarterly, 43(4):456–466, 1995.
  * [24] C. Mesagno, J. T. Harvey, and C. M. Janelle.  Choking under pressure: The role of fear of negative evaluation.  Psychology of Sport and Exercise, 13(1):60–68, 2012.
  * [25] D. Monteiro, A. Wang, L. Wang, H. Li, A. Barrett, A. Pack, and H.-N. Liang.  Effects of audience familiarity on anxiety in a virtual reality public speaking training tool.  Universal Access in the Information Society, pp. 1–12, 2023.
  * [26] B. M. Nes, I. Janszky, U. Wisløff, A. Støylen, and T. Karlsen.  Age-predicted maximal heart rate in healthy subjects: The hunt f itness s tudy.  Scandinavian journal of medicine & science in sports, 23(6):697–704, 2013.
  * [27] R. J. Nesbit and D. Watling.  The role of audience familiarity and activity outcome in children’s understanding of disclaimers.  British Journal of Developmental Psychology, 37(2):230–246, 2019\.
  * [28] H. Palani and N. A. Giudice.  Evaluation of non-visual panning operations using touch-screen devices.  In Proceedings of the 16th international ACM SIGACCESS conference on Computers & accessibility, pp. 293–294, 2014.
  * [29] D.-P. Pertaub, M. Slater, and C. Barker.  An experiment on public speaking anxiety in response to three different types of virtual audience.  Presence, 11(1):68–78, 2002.
  * [30] P. Raimbaud, A. Jovane, K. Zibrek, C. Pacchierotti, M. Christie, L. Hoyet, J. Pettre, and A.-H. Olivier.  The stare-in-the-crowd effect in virtual reality.  In 2022 IEEE Conference on Virtual Reality and 3D User Interfaces (VR), pp. 281–290. IEEE, 2022.
  * [31] F. Raja.  Anxiety level in students of public speaking: Causes and remedies.  Journal of education and educational development, 4(1), 2017.
  * [32] H. T. Reis, M. R. Maniaci, P. A. Caprariello, P. W. Eastwick, and E. J. Finkel.  Familiarity does indeed promote attraction in live interaction.  Journal of personality and social psychology, 101(3):557, 2011.
  * [33] R. M. Ryan, C. S. Rigby, and A. Przybylski.  The motivational pull of video games: A self-determination theory approach.  Motivation and emotion, 30:344–360, 2006.
  * [34] S. R. Schweinberger, H. Kawahara, A. P. Simpson, V. G. Skuk, and R. Zäske.  Speaker perception.  Wiley Interdisciplinary Reviews: Cognitive Science, 5(1):15–25, 2014.
  * [35] S. Serafin, M. Geronazzo, C. Erkut, N. C. Nilsson, and R. Nordahl.  Sonic interactions in virtual reality: State of the art, current challenges, and future directions.  IEEE computer graphics and applications, 38(2):31–43, 2018.
  * [36] P. M. Strojny, N. Dużmańska-Misiarczyk, N. Lipp, and A. Strojny.  Moderators of social facilitation effect in virtual reality: Co-presence and realism of virtual agents.  Frontiers in Psychology, 11, 2020. doi: 10 . 3389/fpsyg . 2020 . 01252
  * [37] D. M. Tice, J. Buder, and R. F. Baumeister.  Development of self-consciousness: At what age does audience pressure disrupt performance?  Adolescence, 20(78):301, 1985.
  * [38] D. M. Tice, J. L. Butler, M. B. Muraven, and A. M. Stillwell.  When modesty prevails: Differential favorability of self-presentation to friends and strangers.  Journal of personality and social psychology, 69(6):1120, 1995.
  * [39] J. Wang, D. Marchant, T. Morris, and P. Gibbs.  Self-consciousness and trait anxiety as predictors of choking in sport.  Journal of science and medicine in sport, 7(2):174–185, 2004.
  * [40] G. Weary and R. M. Arkin.  Attributional self-presentation.  New directions in attribution research, 3:223–246, 1981.
  * [41] A. Westerberg and H. Schoenau-Fog.  Categorizing video game audio: An exploration of auditory-psychological effects.  In Proceedings of the 19th International Academic Mindtrek Conference, pp. 47–54, 2015.
  * [42] W. Xu, H.-N. Liang, N. Baghaei, X. Ma, K. Yu, X. Meng, and S. Wen.  Effects of an immersive virtual reality exergame on university students’ anxiety, depression, and perceived stress: Pilot feasibility and usability study.  JMIR Serious Games, 9(4):e29330, Nov 2021. doi: 10 . 2196/29330
  * [43] W. Xu, H.-N. Liang, Q. He, X. Li, K. Yu, Y. Chen, et al.  Results and guidelines from a repeated-measures design experiment comparing standing and seated full-body gesture-based immersive virtual reality exergames: Within-subjects evaluation.  JMIR serious games, 8(3):e17972, 2020.
  * [44] W. Xu, H.-N. Liang, X. Ma, and X. Li.  Virusboxing: A hiit-based vr boxing game.  In Extended Abstracts of the 2020 Annual Symposium on Computer-Human Interaction in Play, CHI PLAY ’20, p. 98–102, 2020. doi: 10 . 1145/3383668 . 3419958
  * [45] W. Xu, H.-N. Liang, K. Yu, and N. Baghaei.  Effect of gameplay uncertainty, display type, and age on virtual reality exergames.  In Proceedings of the 2021 CHI Conference on Human Factors in Computing Systems, pp. 1–14, 2021.
  * [46] W. Xu, H.-N. Liang, K. Yu, S. Wen, N. Baghaei, and H. Tu.  Acceptance of virtual reality exergames among chinese older adults.  International Journal of Human–Computer Interaction, pp. 1–15, 2022.
  * [47] W. Xu, K. Yu, X. Meng, D. Monteiro, D. Kao, and H.-N. Liang.  Exploring the effect of the group size and feedback of non-player character spectators in virtual reality exergames.  Frontiers in Psychology, 14, 2023.
  * [48] H. Yakura and M. Goto.  Enhancing participation experience in vr live concerts by improving motions of virtual audience avatars.  In 2020 IEEE International Symposium on Mixed and Augmented Reality (ISMAR), pp. 555–565. IEEE, 2020.
  * [49] A. W. Young, S. Frühholz, and S. R. Schweinberger.  Face and voice perception: Understanding commonalities and differences.  Trends in cognitive sciences, 24(5):398–410, 2020.
  * [50] K. Yu, S. Wen, W. Xu, M. Caon, N. Baghaei, and H.-N. Liang.  Cheer for me: effect of non-player character audience feedback on older adult users of virtual reality exergames.  Virtual Reality, pp. 1–17, 2023.
  * [51] M. Zuo and Y. Shen.  How features and affordances of a metaverse portal engage users? evidence from exergames.  Internet Research, 2023.