INOM EXAMENSARBETE MEDIETEKNIK,AVANCERAD NIVÅ, 30 HP

, STOCKHOLM SVERIGE 2020

Mission Climbossible - a study of immersive vertical locomotion in impossible spaces for virtual reality

HEDVIG REUTERSWÄRD

KTHSKOLAN FÖR ELEKTROTEKNIK OCH DATAVETENSKAP

Mission Climbossible - a study of immersive verticallocomotion in impossible spaces for virtual reality

Hedvig ReuterswärdThe Royal Institute of Technology

Stockholm, Sweden

hedvigr@kth.se

ABSTRACTAbstractIn recent years, the edges between reality and virtual reality

have been further smudged as today’s software and hardware

allows for wireless immersive experiences. In an attempt to

solve locomotion as the last piece of the puzzle of perfect-

ing immersive virtual realities, impossible spaces have been

developed to support natural locomotion. This in-between

subject study investigated the effects of the combination of

climbing and free walking on immersion in an impossible

space environment with 20 participants. Users tended to

greatly underestimate the distance climbed (which contra-

dicts a previous study), concentrate, lose track of time, de-

scribe their experience more positively and differently than

the controls group. Signs of spatial, emotional, cognitive and

tactical immersion were shown in aspects of concentration,

time, feelings of freedom, narrative, presence, safety, mental

stimulation and locomotion user strategies to name a few.

Minimal cues may have been present while future studies

might fully confirm and define the immersive potential of

vertical locomotion in impossible spaces.

SammanfattningDe senaste årens utveckling har fortsatt sudda ut kanterna

mellan verklighet och virtuell verklighet då dagens teknik

stödjer trådlösa immersiva verkligheter. I ett försök att lösa

locomotion som det sista biten av pusslet för att göra virtuella

verkligheter perfekta har s.k impossible spaces utvecklats för

att stödja naturlig locomotion. Den här A/B-gruppsstudien

undersökte effekter på immersion med kombinationen av

naturlig och vertikal locomotion i en impossibel space miljö

med 20 deltagare. Användare tenderade att grovt underskatta

längden de klättrade (vilket motsäger en tidigare studie),

koncentrera sig, tappa tidsuppfattningen, beskriva deras up-

plevelsen mer positivt och anorlunda än kontrollgruppen.

Tecken på rumslig, emotionell, kognitiv och taktil immersion

visade sig i form av koncentration, tid, känslor av frihet, nar-

rativ, närvaro, säkerhet, mental stimulation och locomotion-

användarstrategier för att nämna några. Minimala element

kan ha uppnåtts medan framtida studies kan bekräfta och

definiera den immersiva potentialenmed vertikal locomotion

i impossibel spaces till fullo.

KEYWORDSVirtual Reality. Human-Computer Interaction. Virtual en-

vironment. Virtual Reality. Immersion. Locomotion. Natu-

ral locomotion. Vertical locomotion. Climbing. Motion mea-

surement. Player experience. Game experience. Navigation.

Human-centered computing.

1 INTRODUCTIONAlready in 1965, virtual reality was predicted to have the

potential of being the Wonderland of Alice with proper im-

plementation [51]. In recent years, the growing possibilities

with virtual reality have made it possible to further smudge

the edges between reality and virtuality [16]. Virtual reality

headsets have been developed to support more and more

advanced interactions and can now provide a more seam-

less experience of virtual reality [16]. These so-called Head-

Mounted Displays (HMDs) can be used freely by the user

that controls the position and view by moving their head to

look in all directions. Previous generations of HMDs allowed

only for rotation of the head but with the rise of popular

headsets such as Oculus Rift and HTC Vive tracking of the

heads position is provided [7]. These systems implement

what is called six Degrees-of-freedom (D-O-F) which refers

to 3 coordinate variables with 3 rotational angles [40]. In

that way, the first person perspective technique supports

a responsive and unrestricted experience. Due to this free

nature, virtual reality applications are applicable to explore

by moving your whole body such as normal walking [7].

Subsequently, one of the major technical concerns with vir-

tual reality has been that it is inconvenient that the user is

electronically tethered with wires to the headset from the

machine that drives it [8]. This has been solved with the

development of completely wireless headsets such as Oculus

Quest and HTC Focus that can be used on its own [12].

Nevertheless, large virtual environments are difficult to

explore by foot due to the often limited space the user has

available[7]. While there have been advances in virtual re-

ality regarding wireless and free axis rotation and position,

there still exists a complication regarding free movement

in virtual reality. Even if the user might be able to rotate

and traverse freely, their surroundings are often more re-

stricted when it comes to the available physical space. Large

1

virtual environments cannot be explored freely by foot if the

physical space does not amount to the virtual in size. How a

user self-propelled moves in the virtual is a technique called

locomotion [7].

There have been many approaches to implement loco-

motion in virtual reality to combat this problem where the

physical and virtual space is not spatially equal, limiting the

experience. In the past, both hardware or software have been

used to implement different locomotion techniques. Methods

that involve adding hardware in the form of omnidirectional

treadmills, footpads and rotating parts are often very expen-

sive, bulky and intricate in installation and aims to extend

the available physical space [15; 29]. Studies have shown that

just moving freely without the use of hardware feels more im-

mersive than using controllers or additional hardware such

as the Virtusphere . Software solutions for locomotion have

therefor been used which require less technology, set up for

the user and are less fatiguing. With the help of controllers,

the user traverses in the virtual world while being relatively

still in real-life. There exist different artificial locomotion

techniques which both allow for movement in the horisontal

and vertical space. For clarity, techniques such as climbing,

usage of elevators and stairs can be referred to as verticallocomotion which aims to move the user vertically [4]. Due

to the stationary nature of artificial locomotion, these loco-

motion techniques are called artificial locomotion. In contrast

to free walking which is referred to as natural locomotion,artificial locomotion can produce motion sickness in its users

and reduces immersion[4].

Subsequently, the art of perfecting immersive locomotion

has not yet been mastered. As free walking allows for the

highest immersion, the spatial differences in virtual and phys-

ical worlds are problematic [16]. Here enters the concept of

impossible spaces. In order to maximise the physical area, a

way to develop for higher immersion has been proposed. The

structure of an impossible space re-uses the physical space

by redirecting the user away from the limits of the physical

available space. This creates an illusion of a never-ending

space that produces a more seamless and immersive virtual

reality experience [16].

In recent years, studies of these relatively new virtual

design concepts of impossible spaces have been made into

exploring how natural locomotion affects perception and

experience of impossible spaces [49]. As these architectural

layouts are built as a solution for providing a suitable en-

vironment to natural locomotion, there has not been that

much research into the limits of locomotion techniques in-

side impossible spaces and there is more knowledge to gain

in understanding the experiences and limitations of impossi-

ble spaces.

1.1 Research questionThe aim of this thesis study is therefore to determine any

limits to the natural locomotion impossible space with a

vertical locomotion technique. The study would investigate

how you come to use impossible spaces by combining free

locomotion with vertical. In extent, this could show if ver-

tical locomotion in that sort of space can be added without

affecting the immersion of the virtual reality space.

How does combining vertical and natural locomotion in animpossible space affect immersion in virtual reality?

1.2 DelimitationsSoftware-wise, only one vertical locomotion technique will

be investigated together with natural locomotion in this

study as analyzing many different vertical locomotion tech-

niques would demand more time and resources than the

scope of the thesis. Therefore, one vertical locomotion tech-

nique will be chosen to go forward and implemented. More-

over, no more components and elements needed for testing

will be implemented in the environment. In regards to the

impossible space, only the self-overlapping functionality will

be included in the prototype. No other content than the lo-

comotion and space algorithms itself will be added unless

needed to apply some form of purpose to exploring the lo-

comotion in the virtual environment for the clarity of tasks

and instructions. That is to say, the virtual environment will

solely function for the scope of the testing of the research

question.

Hardware-wise, the test platform will be restricted to one

HMD model as support for more platforms are unnecessary

for the study test design.

2 THEORY AND RELATEDWORKSRelevant concepts and studies will be described below. In

large, related experiments made in the area of locomotion

will be focused on in conjunction with impossible spaces

that is the context that sets the scope of the research area

question. The different aspects of so-called immersion will

be presented.

2.1 Immersion and presenceWords that are often deeply connected to studying virtual

reality are immersion and presence. The layman’s defini-

tion of the word immersion is defined by the Oxford Dictio-

nary as "immersion (in something) the act of putting some-

body/something into a liquid, especially so that they or it are

completely covered; the state of being covered by a liquid"

and "immersion (in something) the state of being completely

involved in something" (Oxford University Press, 2020) [1].

In the field, there exist different definitions to describe the

2

relationship between immersion, presence and virtual real-

ity.

An early definition by Slater states that immersion is a level

of sensory that a virtual environment system can provide

while presence is the user-dependent responses to the sys-

tem. In that way, immersion is defined by the technology

in the form of display and rendering and is objective. In

contrast, presence is subjective and based on the psycho-

logical responses and depends on different factors such as

experience, history, state of mind, etc. Aspects that deal with

immersion would for instance be display resolution, field of

view, the realism of lighting, frame rate, rendering quality.

Specifically, presence would entail feelings on "being there"

and bring about feeling that would emerge in real-life in

similarly resembling situations. Other impressions that deal

with emotions, involvement and interest are separate from

these terms and are defined as the content of the experience

[44].

Another definition describe immersion as a sense of spatially

being present in the virtual reality environment and being

disconnected from time and space in real-life as immersion

[17]. Moreover, presence has also been used to measure how

effective virtual reality environments are and in this sense

would describe the extent of the feelings of "being there"

would be but also includes interaction, environmental fac-

tors, etc. of the subjective individual experience [60].

The Slater definition does not consider the emotional as-

pect of an experience, the latter and the former does not

entail what both presence and immersion exist of. Another

definition of the word is given by Björk and Holopainen.

According to them, immersion can entail four different cate-

gories: spatial, emotional, tactical and cognitive immersion.

These deal with matters of how convincing the environment

is, how emotionally invested the user is in terms of narration,

sensory feedback and mental challenge. Spatial immersiondepends on the user’s perception that the simulated world

feels real and they really are "there". Emotional immersiondeals with user involvement and investment in the story

and narrative. Tactical immersion is sensory-motoric and is

associated with actions that are rhythm-based and naturally

repetitive. In particular, this would be actions in conjunc-

tion with rhythm-based stimuli such as visual, auditory or

sensory in the form of music, representation of objects, etc.

Lastly, Cognitive immersion can occur with different levels

of mental challenges. Strategic immersion like this is asso-

ciated with decision-making in a goal-based scenario that

could be independent of the physical world [3]. Some of the

previously mentioned definitions fall short and do not sum

up the spectra of a virtual reality experience whether it is

effective or not. In particular, what Slater calls the content of

the experience could fall into the categories of the emotional

immersion in [3]. Additionally, not all aspects of virtual re-

ality seem to be the only way of creating immersive virtual

reality as studies have shown that not all parameters of vir-

tual reality experiences are equally important. For instance,

realism has been shown to be inferior to frame rate, inter-

action, sound, head tracking and so-called "minimal cues"

details howminimal certain elements can be in order to bring

about feelings of presence [42]. In that way, many aspects

need to be taken into consideration. On the topic of realism,

studies have argued that realism should not be taken into

consideration in virtual environments that are abstract or do

not resemble real-life [6]. Clearly, there are many different

opinions on the area of immersive virtual reality. For the

purpose of this thesis, the definition of immersion will be

characterised by the definition of Björk and Holopainen as

this provides the most versatile application. The meaning of

the word presence as in the presence questionnaire used in

the method (See section 3) will be used in coherence with

other tests to provide a fuller basis for the thesis. The word

presence will entail the feeling of spatially being there as

spatial immersion in Björk and Holopainen’s definition.

2.2 Wireless headsetsThere are two different kinds of tracking used in virtual

reality optical systems. The first is called outside-in which

uses sensors and systems outside of the headset [41]. For

example, it can use using room-scaling and outside trackers

with cameras or beacons [16]. Contrary to this, a inside-outconfiguration has its sensors inside of the headset. Thus,

inside-out tracking systems can be wireless. By attaching

cameras or multiple other sensors to the target and uses

scanning of rotating mirrors or cameras inside-out headsets

measure both orientation and position in the room. They

often render in higher resolution and produce more accurate

values of position than outside-in systems [41]. Headsets

such as Oculus Go. Oculus Quest and HTC Focus are called

stand-alone systems since they are wireless and requires no

external trackers or computers to run it. The newly released

Oculus Quest has 6 D-O-F similar to the HTC Focus which

makes it possible to track it with all three axes of positions

and rotation to keep track of not only sitting or standing

but also moving around freely [12]. In that way, it is very

natural to use these HDMs by using your whole body as the

tracking follows your first-person perspective. Completely

free movement like infinite free walking is consequently

possible in theory but in practice becomes troublesome as

exploring a vast virtual environment is hard to map directly

onto a smaller limited physical area [7].

3

2.3 LocomotionThis spatial problem of the difference in the user’s physical

space compared to the virtual space is tackled by the con-

cept of locomotion. The often limited physical space restricts

infinite walking and completely free movement [16]. Differ-

ent locomotion techniques have been developed and these

could be divided into categories such as natural and artificial

locomotion [29].

2.3.1 Natural locomotion. This form of locomotion lets the

user move completely self-propelled usually by foot in both

the virtual and physical worlds. In that way, it is maneu-

vered and controlled by the user’s navigation and speed. In

that way, there is no use of any software mechanics or con-

trol devices [53]. As natural locomotion entails that a user

can walk freely within the virtual space, natural locomo-

tion is highly immersive but require more of the physical

space it is limited to in order to provide infinite walking [4].

There are different approaches on how to implement this

by the use of hardware and software [29]. The invention of

forward-moving treadmills for virtual reality that dynami-

cally responds to any physical movement forward [14], [24],

[38], omnidirectional treadmills [11], [35], [19], [46], omni-

directional surfaces using motorised tiles [20], motorised

strings attached to the user’s shoes [22] as well as hamster-

wheel like virtuspheres [28] have been tested. The results

have varied in quality, often prohibits the user from moving

side-ways and the possibility of falling when losing their

balance at turns [5]. Owing to the fact that these complex se-

tups are expensive and troublesome in their installation, one

has often looked for implementing natural locomotion on its

own without the use of hardware. They have also proven to

be less immersive [29]. There has also been development into

treading platforms such as gait turntables that lets the user

walk freely while remaining stationary. Simulating uneven

surfaces, it can be used to ascend and descend staircases.

The motion platforms underneath each foot rotate to allow

for movement in all directions. The study needed further

implementation of the hardware as it was not yet combined

with a HMD and full evaluation of presence perception in

immersive virtual environments [21].

2.3.2 Semi-natural locomotion. To overcome the issues with

restricted physical space and still strive for natural locomo-

tion, self-motion gain techniques were introduced with the

goal of preserving the benefits with natural locomotion while

discretely altering an aspect of the user’s motion in the vir-

tual world. This is unknown to the user and is accepted by

the mind within certain limits as visual stimuli are often fa-

vored compared to body awareness and balance [49]. These

techniques are also called redirected walking [36].

There are three different categories to the so-called manipu-

lation of self-motion techniques. Translation gain techniques

translate changes in the physical coordinates of the virtual

system and scale it for the smaller or bigger virtual environ-

ment, rendering the applied change. Rotation gain instead

translates orientational changes and scales for the rotation

in the virtual environment. These usually aim to steer and ro-

tate the user from colliding with the outskirts of the physical

area. There exist different implementations such as rotating

the user while the body is moving around obstacles or when

the user’s body is still but is turning their head [49]. Another

approach is rotating the scene whenever without warning

[36] or distracting events that rotate the scene [37]. Curva-ture gain techniques consistently offset the user’s movement

either while they are turning their head or when they move

in a straight path. Doing so results in the user compensating

for the manipulated stimuli and will walk in circular arcs

[49].

2.3.3 Artificial locomotion. Artificial locomotion requires

interaction from the user to a system such as hardware in the

form of a controller. It is less physically fatiguing as the user

can stay in a static position through the experience and move

by input through a controller. Different forms of artificial

locomotion are teleportation, smooth locomotion (sliding by

the use of a joystick), arm swinging, gesture-based, walking

in place, etc. Since the user moves in the virtual but stays

stationed in the physical space, artificial locomotion often

leads to motion sickness. As opposed to natural locomotion,

artificial locomotion is less immersive [4].

2.3.4 Vertical locomotion. There exist different locomotion

techniques to date that lets the user move both horizontally

and vertically. Tomove in the vertical space, elements such as

elevators or stairs could be used. Climbing is also a locomo-

tion technique for the horizontal plane. Further on, verticallocomotion will be referred to as techniques that allow the

user to move vertically within a virtual space. An example

of this is climbing.

2.4 Locomotion studies in immersionThere have been studies that show that some artificial lo-

comotion techniques could be more useful than others. In

1995, Slater et. al showed that walking-in-place locomotion

produces a higher sense of presence than flying (by the push

of a controller button) and pointing. If the walking-in-place

technique is well implemented, it can be perceived as tho

the user is walking. It can be explained by the activity of

normal walking is so similar to the operation of walking

without the need of any mental calculations into another

form of movement not similar to walking to navigate in the

desired direction. Slater et al. also argued that climbing could

be seen as quite similar to walking-in-place but depending

4

on the position of the hands rather than the position of the

headset. The climbing was implemented to be steered by leg

movement once the user and the bottom or top of the stairs

had collided. Climbing up was achieved by moving your feet

while turning around resulted in climbing in the opposite

direction. In cases of climbing and walking up/down ladders

or stairs, it is suitable for meaningful and mundane activities

with a high level of realism as it involves a whole-body ges-

ture. It is not useful for magical interactions such as flying.

Moreover, the use of all limbs could enhance the user’s con-

nection to the virtual avatar body which increases presence

[45]. climbing are interactions that are reminding of real-life

movements, they could indeed be perceived as more realistic

and therefore more immersive. In fact, mundane locomo-

tion techniques that mimic real-life physical interactions are

deemed as easier to use since they remind users of realistic

scenarios and can be applied logically in those. In general,

lower-body movements are often preferred as they resemble

real walking the most [34].

In 1999, the Slater studywas replicated and natural locomo-

tion was added to be used in comparison to walking-in-place

and press-button-flying. The 1995 findings of higher pres-

ence in walking-in-place than flying were again confirmed.

More importantly, both real walking and walking-in-place

demonstrated presence compared to flying. In particular, real

walking provided a compelling virtual experience. This study

also indicated that two parameters could affect the effective-

ness of locomotion techniques. The walk-in-place technique

could be improved with the addition of a hardware acceler-

ator and the level of association to the virtual body plays

an important part. Subjective presence was significantly in-

creased with the customization of the virtual avatar for a

better degree of association and all limbs tracked [54].

Numerous studies into the benefits of the use of natural

locomotion have beenmade. It has often tested in comparison

to artificial locomotion that uses controllers and shown to be

advantageous in many ways. Research has shown that free

walking is more efficient in spatial navigation, searching and

natural path-finding. It also provides a smoother experience

traversing as collision with virtual objects is decreased. It is

also beneficial in cognitive aspects as attention levels and

mental processes are higher. However, artificial locomotion

is more than often implemented in virtual environments due

to the impossibility to map the physical movements to the

virtual and let the user explore freely [49].

Similar to free walking, studies in redirected walking have

shown potential. This semi-natural locomotion technique

has proven to be non-inducing when it comes to motion

sickness and goes unnoticed by the users whom unaware

adjusts their direction [39]. Further studies have shown that

in some contexts semi-natural locomotion techniques need

proper implementation. Research has shown that in order for

redirected gain techniques to work without fail, sometimes

curvature gain techniques are combined with the other two

methods. Also, the use of distracting elements tends to be a

more effective stimulus than auditory or visual instructions

to produce head turns in the user when needed to reorient.

Studies have concluded that redirected walking is superior

to both walking-in-place and other control-based artificial

locomotion techniques in relation to pathfinding and navi-

gation. When implemented suitably with distractors, it was

as adequate as real walking in sketching maps and pointing

to targets [49].

Looking from another perspective, upper-body artificial

locomotion has been proven to produce natural experiences.

Indeed, it might not coerce with the idea of achieving in-

finitive free walking [34]. However, one study compared the

gesture of arm-swinging to natural walking and joystick

locomotion and found no significant difference in spatial ori-

entation results between arm-swinging and walking though

it outperformed the joystick. The arm-swinging locomotion

technique leads to less fatigue and could be used regardless

of any space limitations [27]. Another study claims that arm

swinging was closer to real walking in levels of energy con-

sumption than lower-body hip movements and controller lo-

comotion. Moreover, it showed high levels of naturalness and

less positional drift was measured from arm-swinging [33].

In the particular case of upper-body locomotion techniques

such as arm-swinging, a further study had somewhat more

different results than this previous work. Arm-swinging con-

sistently overestimated distance to objects in blind locomo-

tion tests where the user first views the virtual environment,

then in darkness moves to where the user thinks the target is

located. Here, normal walking tended to underestimate target

distances which have previously been suggested in regards

to visual distance estimations. Not surprisingly, there were

lower levels of errors in turning in real walking compared to

arm-swinging and walking-in-place. The two former were

statistically equal to each other. Walking-in-place appeared

to be the most accurate, proposing that free walking induces

users to be more careful as they feel less comfortable with it.

Nevertheless, arm swinging was seen as a robust locomotion

as walking-in-place as it is inexpensive, independent of room

constraints and to the lack of occlusion [58].

Seemingly, most locomotion research focuses on horison-

tal movement. Often, vertical locomotion in the forms of

flying has been investigated and uses control devices to for

example choosing the desired height by pressing buttons,

joystick steering and flying through hand-tracking gestures

[25]. After Slater, climbing was once again explored. This

time, climbing up and down ladders was enabled and proved

to have less latency than joystick locomotion. No other find-

ings were relevant as presence of the climbing technique was

not the main focus of the study [52]. Later, by marching in

5

place while grabbing onto the ladder with the use of buttons

of a controller, a more realistic implementation of climbing

was achieved compared to both predecessors [25]. Locomo-

tion in the form of vertical elevators has also been examined

and demonstrated a high sense of spatial presence and nat-

uralness in comparison to teleportation through joy stick

and flying [57]. Distance estimations of walking vertically

up and down different kinds of stairs have shown to be more

accurate without haptic feedback but more immersive with

passive haptic feedback in combination with physical objects

to tread on [30], [31]. To some extent, height perception has

been studied in regards to eye height and object perception

but no further investigations of height perception in im-

mersive virtual reality using vertical locomotion techniques.

One study examined the estimation of distance when ascend-

ing and descending stairs. On the whole, users tended to

over-estimate the distance ascended/descended which previ-

ous work has also suggested. Here, the self-representational

avatar played a significant part as users estimated more accu-

rately in a combination of virtual feet thanwithout. Open sur-

roundings were also proposed to contribute to better height

estimation [2]. Just recently, one study focused on vertical

locomotion using both hands and feet to move vertically

by climbing ladders. Both haptic feedback and audio-visual

cues were implemented in a climbing ladder scene. By using

all limbs naturally, the experiment aimed to practice safe

climbing. Using relatively inexpensive portable hardware,

the technique was perceived as natural. In particular, the

ladder technique resulted in high levels of proprioception.

Ultimately, the intuitive full-body interactions achieved a

realistic feeling of ladder-climbing while users also reported

progress in learning [23]. This confirms the prior findings

as full-body locomotion of climbing increases presence with

mental association with the avatar.

2.5 Impossible spacesSemi-natural and artificial locomotion techniques are all

methods of self-motion manipulating techniques. The other

way around, the actual virtual space could be adjusted for

the user. In fact, this area has not been studied as extensively

as self-motion manipulated techniques. As infinite free walk-

ing is only possible in virtual realities that can fit inside

the available psychical space, one could instead design for

maximizing the virtual environment in that area in order to

provide for both natural locomotion and immersion. Propo-

sitions like virtual portals and change blindness illustrations

have been used to continuously and immediately redirect

the user in the physical space that has gone unnoticed by the

users. Impossible spaces could be defined as self-overlapping

architectural layouts that when entered, are bigger on the in-

side. The room itself is not physically possible and wouldn’t

be possible to experience in real-life. New areas continuously

emerge on the edges of a space, overlapping or altering the

current structures. These synthetic worlds that maximises

the virtual area upon a reasonably-sized physical area are

only accessible in virtual reality where the user have the

potential of moving completely naturally or semi-naturally

[49].

A first prototype impossible space was used in a 2011

study that combined the concept with testing the efficiency

of change blindness. Using this particular virtual space which

was a little more than twice as big as the physical, the virtual

office environment was made up of corridors and 12 desk

rooms (See Figure 1). When a user approached a desk in a

room, the rotation of the door changed and the user could

then go into the next room and so on. In this study, just

one of 77 participants noticed the impossible space structure

with the change blindness element and showed a high level

of presence [48].

Figure 1: Example of the bigger virtual space than psychicalspace with change blindness & Suma et al, via IEEE Xplore.(https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/5753662/5759414/5759455/5759455-fig-2-source-small.gif).

Then, one study introduced the term of impossible space

and solely investigated the limits of impossible spaces. On

this occasion, the virtual space kept on unfolding in front

of the player’s path (See Figure 2). No distraction elements

were used. It was shown that rooms inside impossible spaces

can overlap by a certain percentage without the effect being

noticeable. It was shown that spatial-visual stimuli are clearly

perceived as malleable by users and suitably can be explored

by natural locomotion. The experience of the impossible

spaces was most immersive when users were unaware of the

nature of the artificial virtual space they were in. Moreover,

the user’s perception of distances to targets was not affected

even if users had recognised the impossible architecture [49].

Another study developed this idea further with the idea

of procedurally generating possible structural rooms for a

more general appliance. This research indicated that if the

focus of the virtual experience is less on the spatial struc-

ture and more on the content, generated impossible spaces

could be used in conjunction with redirected walking. In

this case, procedural rooms could be generated and used

6

Figure 2: Example of an impossible space environment.The two rooms overlap spatially. As the user traverses thearea, the space will shift between two states in order toachieve a consistent view for the user. & Suma et al, viaIEEE Xplore. (https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/2945/6165123/6165136/6165136-fig-1-source-small.gif).

with change blindness elements which granted the user infi-

nite free walking through redirected walking(See Figure 3).

These so-called flexible spaces could then be used to model

many more different rooms in an environment than the two

rooms that shared a wall in the previous impossible space

experiment. Again, the recognition of the physics-defying

world was not straightforward as users found themselves in

a familiar world and did not notice the unusual nature of the

space [56].

Figure 3: Procedural generation of impossible spaces calledflexible spaces. a) the layout is dynamically generated witha corridor between a blue and yellow room that is shiftedas the user exits a room (change blindness). b) the user’snavigation is shown in the physical space. c) some generatedflexible structures & Suma et al, via IEEE Xplore. (https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/6542296/6550177/6550194/6550194-fig-1-source-small.gif).

Since then the development of impossible spaces struc-

tures has been developed, often in combination with redi-

rected walking. The use of curved corridors has been shown

to be combined with redirected walking in impossible spaces

[26]. Indeed, curved corridors have been suggested to be pre-

ferred over straight right-angled corridors with redirected

walking [55]. Studies have also been made into achieving

high-quality performance with impossible spaces in combi-

nation with redirected walking into minimising unnecessary

distortion and globally mapping a set of virtual spaces to

real spaces [50] [13]. Also, grid-based artificial intelligence

approaches into solving for angle-constrained path findings

have been introduced and attempts to generate perfect maze

paths with desired properties [61]. Lastly, computational in-

telligence algorithms have been applied to dynamically steer

and redirect the user [47].

Clearly, much of the existing research has investigated the

structural effectiveness of generating impossible rooms. Only

last year, one study was made into furthering the user expe-

rience of an impossible space and sought to generate experi-

ences on the go, rather than perfecting a structural layout,

which resulted in high levels of immersion. In real-time, ani-

mations and virtual objects were produced to dynamically

block the user’s view or hide structural changes and guide

the user to navigate in the space. If the physical area was

changed or in the case of emerging obstacles, the structural

area would reflect these dynamic changes and manage the

applicable virtual scene changes. [10]. Furthermore, an im-

possible space in the shape of a cave with a size of 4x3 m

was navigated by natural locomotion and climbing in a pro-

totype study. All surface of the walls was climbable while

the user could move freely horisontally, sometimes needed

to crawl through tunnels the users hacked through walls.

The experiences were perceived as very natural and highly

immersive, especially at times when users needed to crawl,

shimmy and climb. Users themselves credited the use of

crawling, shimmying and climbing to the high immersion

[18]. Subsequently, more research into these findings is yet

to be made to confirm the evaluations of presence.

Locomotion-wise, on top of the benefits from natural loco-

motion real walking, it could have even more benefits inside

impossible spaces. Here, the vestibular information that is

received by the user when actually moving could be con-

tributing to the spatial understanding and perception of the

size of the virtual environment [5]. In comparison, redirected

walking could instead put more stress on cognitive load as

the user needs to physically compensate and redirect oneself

according to the visual stimuli [9].

Subesquently, there is a need for further work into immer-

sive locomotion techniques in virtual reality. Real walking

has already been shown to be natural and most intuitive,

providing the most sense of presence. Yet, there is a lack

of research into vertical locomotion in virtual multi-level

environments. To the best of my knowledge, no prior work

has investigated vertical locomotion inside impossible spaces

fully in terms of evaluation into immersion. This work can

be seen as extended the impossible space study consisting of

a cave that was possible to explore with the use of natural

locomotion and climbing and seeks to push the boundaries

within vertical locomotion in impossible spaces.

7

3 METHODFirstly, the pre-study was based on related work and laid

the foundation for the scopes of the thesis study. When a

prototype had been developed and tested with pilot tests, an

in-between user study with participants took place testing

out the immersion of the virtual reality space that imple-

mented both natural and vertical locomotion.

3.1 Pilot studyThe testing of the prototype was crystallised through the

practice of trial-and-error in the pilot user tests. Five volun-

tary pilot users between the age of 29-69 with and different

levels of acquaintance with technology in general and no

prior experience of virtual reality. Through iterating, the test

design was altered and adjusted according to the insights

from each pilot test. These highlighted scientific weaknesses

in the execution of the study design such as the potential

need to adjust environmental variables, amount of instruc-

tions, clarity of questions or interview techniques used in the

next iteration. These changes would then be implemented

and be included for the user studies in order to perform valid

user tests that would yield the highest level of scientific and

accurate results.

3.2 ParticipantsThere was no need for any particular requirements in expe-

rience to qualify for taking part in the user tests other than

being able to walk unassisted. However, due to the extraordi-

nary circumstances with covid-19, each test person needed

to have access to the model of the virtual reality headset

as the majority of all the user tests needed to be performed

remotely. By word of mouth, participants which owned or

had other access to the Oculus Quest headset were fit to

take part in the experimental test. It was preferable to have

between-subject tests with A and B groups as the impossible

space with free locomotion would be tested with and without

vertical locomotion. In contrast, within-subjects would not

be preferred since the order of test environments would af-

fect a user’s experience. The total number of 20 participants

was divided into two groups, group A and B, with 10 persons

in each group. Each group corresponded to one case of the

prototype. Group A was able to use both natural and vertical

locomotion whereas group B could only make use of natural.

In that way, group B served as the control group of the user

study. After the test of the prototype, both groups filled in

a questionnaire and were interviewed in the same way. A

set of mutual questions was used for both of the group’s

interviews but group A answered some additional questions

as well that dealt with the aspect of vertical locomotion.

The division between each group was random. It resulted

in group A consisted of 4 females and 6 males between the

ages of 26-69. They had different levels of prior experiences

with VR, ranging from being well acquainted with the tech-

nology to being their first time experiencing virtual reality.

One female and 9 males between 25-69 made up group Bwith

similar experience as group A, from none to experienced.

About half from each group were familiar with the concept

of impossible spaces before.

3.3 Test designEach test would follow the same structure to reduce inconsis-

tencies between tests and other effecting factors. The length

of each test ranged from 45 minutes to about 1 hour 15 min-

utes, for group B respectively group A. The longer test time

for group A was due to the additional questions asked to

them regarding the vertical locomotion. All tests were con-

ducted on-to-one in their mother tongue. The majority of

the tests were remotely and made via video calls between

the study moderator and the test user. Each test would begin

by allowing the user to sign a consent and confidentiality

agreement which stated the voluntary aspect of participating

in the experiment, anonymity of data and any rights to termi-

nate the test if needed. The purpose of the consent form was

to ensure the integrity and voluntary aspect of taking part in

the study. After, they were given the task of touching cubes

and rectangles by either walking up to them (group B) or both

walking and climbing to reach them (group A). They were

given short and concise instructions for how to move and to

explore the space with the locomotion techniques provided

in order to find all cubes and rectangles. Subsequently, the

user entered the virtual environment and a screen recording

was made. During their walk, the study moderator interacted

as little as possible with the test user to avoid distraction

and only answered questions and gave guidance if needed.

When the user terminated their walk test data was produced

and sent to the moderator. The measurement taken was:

• Time of completion: the total time the user spent in

the environment

• Time walking: the total time the user spent walking

in the environment

• Time climbing: the total time the user spent climbing

in the environment (applicable for group A)

• Walking distance: The virtual distance the user moved

using walking as locomotion

• Climbing distance: The virtual distance the user moved

using climbing as locomotion

• Video: The view of the user’s virtual experience was

recorded

• Grip points: How many grip points were used by the

user in total (applicable for group A)

8

• Number touched objects: A control number to make

sure the user had indeed followed instructions to touch

cubes and rectangles

Ensuing their walk, a questionnaire was presented to the

test user either in person or by sharing screens in the video

call. Initially, the user was asked to provide an estimation

of some measurements of time and space. These were as

following:

• The height of the user

• Perceived time of walking: how long the user thinks

they spent walking in the environment

• Perceived distance ofwalking: how long the user thinks

they travelled by walking in the environment

• Perceived time of climbing: how long the user thinks

they travelled by climbing in the environment (appli-

cable for group A)

• Perceived distance of climbing: how long the user

thinks they travelled by climbing in the environment

(applicable for group A)

Finally, the interview part took place. A questionnaire and

open questions served as a semi-structured interview with

the master thesis student as the interviewer and the test user

as the interviewee. The user filled in, with the help of the

study moderator, an adapted version of the presence ques-

tionnaire by Witmer and Singer [59] which is a conventional

questionnaire from 1998 which is the most cited presence

questionnaire on the scholarly search engine Google Scholar

[43]. The last part of the questionnaire was open-ended ques-

tions with topics such as the sense of motion and impressions

of different locomotion techniques in the impossible space.

When the interview was terminated the screen recording

was obtained by the study moderator.

3.4 PrototypeA virtual reality environment was developed for the Oculus

Quest headset. As the headset is wireless, it was a suitable

model to use when exploring the limits and experiences of

impossible spaces. The impossible space environment was

developed in conjunction with natural locomotion and the

vertical locomotion technique of climbing. The graphics of

the prototype was minimised, using neutral grey colors and

as little design details as possible as can be seen in the screen-

shots of a virtual walkthrough of the prototype in Figure 4,

5 . The prototype consisted of floor, walls and roof made of

simplistic cube design to accommodate an impossible space.

White cubes and rectangles were placed inside this space

for the user to touch during their experience by walking or

reaching by climbing. The cubes were spawned at a maxi-

mum height of approximately 2 m to make sure they could

all be reached by the walking users. The parallelepipeds (the

rectangles) were placed at a height where users needed to

climb in order to reach them. No other objects or mechanics

were introduced in the environment except for the impossible

space structures and the objects needed for the experimental

tasks needed for the locomotional exploration. Owing to this,

the environment aimed to only test the natural and verti-

cal locomotion in practice. The virtual reality camera object

which was corresponded by the player itself originated from

the Oculus OVR Camera Rig object. The choice was made

to use the standard 3D models of the hand controls for the

user’s hands as this would look familiar and exclude any

other distracting design that could affect the experience. The

climbing mechanism was implemented so that the user could

use both hands separately and could be triggered by placing

a hand close to a surface and pressing the index finger button.

By continuing to pressing that button, the user could pull in

the opposite direction of the desired direction and the user

would be moved correspondingly. By releasing the button,

the user would release their grip and their movement would

be paused. Due to the fact that artificial locomotion such as

falling could induce motion sickness, the ability to fall was

excluded to minimise factors that could result in affecting the

user negatively and the validity of the test. To illustrate, in

order to climb upwards a wall the user would pull at the sur-

face downwards and the camera would move upwards. Upon

the release, the player would have subsequently moved. A

user could look around 360 degrees during a grip to the wall,

making the climbing quite flexible in its rotation and move-

ment in action. The walking locomotion demanded little to

none implementation as the camera rig objects correspond

to the user’s exact head and arm movements. By pressing

one of the buttons, the user could quit the application which

marked the end of the prototype session.

Figure 4: The virtual environment prototype

3.5 InterviewThe interview was divided into 2 main sections, the question-

naire and the open-ended questions. In the first questionnaire

part, the user would rate their responses to questions re-

garding a sense of control, motion, realism and involvement

9

Figure 5: The virtual environment prototype

on a Likert-scale from 1-7. The questionnaire was divided

into four sections - control and sensory, distractions, real-

ism, involvement with around 3-4 questions per section. The

last part with open questions aimed to let the interviewee

describe their experiences and feelings from different per-

spectives. The areas discussed were impossible spaces, the

sense of motion by the use of the different locomotions, con-

tributions or distractions from their experiences and general

feelings or impressions that had come up during the test. Fol-

low up questions were asked by the interviewee if the user

gave an unclear answer or needed to explain their answer

further. Group A was asked a set of additional questions

about the sense of vertical locomotion as they could also use

climbing. Some of these questions discussed the difference in

feeling as opposed to walking, contribution to experiences

and impressions.

The qualitative data was dealt with in accordance with con-

ventions of qualitative data collection analysis. The inductive

approach was identified as suitable for the thesis scope and

the framework used is the explanatory as the research ques-

tion guides the analyse. In that matter, the data was examined

to answer the research question [32]. In that fashion, the data

was first transcribed, summarised and cleaned for further

analysis. The participants were given aliases of A1-A10 as

well as B1-B10 for avoiding any bias and maintaining the

objectiveness of anonymity. Manual coding was performed

in iterations leading ultimately to the use of the following

codes: claustrophobia (in regards to small spaces), movement,freedom, exploration, change (environmental change inside

environment), confusion, naturalness, safety (emotionally and

physically), limitations (software-wise, hardware-wise, phys-ical restrictions), weight (of one-self and objects), sickness(such as motion sickness, VR-sickness, fear of heights), fa-tigue, speed (physical speed and task speed), complement(comparisons of locomotions). With these codes, the data

was sorted in regards to opinions, feelings, knowledge and

other input. These areas were then, in turn, analysed to iden-

tify patterns, themes and differences. Lastly, 2D word maps

were made using Adobe Photoshop v. 21.1.3 based on the

words chosen by the participants when asked to describe the

walkthrough emotion-, impression- and experience-wise in

three words.

3.6 TechnologyThe headset used was the Oculus Quest and the software ap-

plication was developed using version 2019.2.3f1 of Unity3D

engine. The tests that were conducted remotely were made

through Google Meet video calls. The data from each test

was sent through using ElasticSearch with the framework

Kibana.

4 RESULTSThe results from the study will be presented below in the

three parts: estimations, questionnaire and interview where

each part will be shown in turn.

4.1 Time and distance estimationsThere was no significant difference in the time estimations

between the two groups. On the whole, both groups underes-

timated their time spent with each locomotion with a factor

up to 2-3 times the time they had spent on it in reality. In

both groups, there were people who overestimated the time

spent. Six participants in Group B underestimated with a

factor between 0.5 to 2 times, one guessed approximately

correctly and three participants in Group B overestimated

the time spent with a factor of 0.5 to 0.75 times the actually

spent time, Group A seemed to underestimate their time

spent with the locomotions to often 1-3 times longer than

the actual time. About three people guessed approximately

the time, five persons underestimated the time with a factor

between 0.5 and 3 times the real-time spent with the loco-

motion. One person overestimated their time with a factor

of 0.7 times. Due to software issues, the data accumulated

from one of the tests was lost and therefore no comparison

can be made with the estimations from that test.

On the whole, both groups underestimated the traversed

distance similarly though group A tended to underestimate

walking slightly more than group B and climbing by a large

factor. The participants in control group B estimated distance

walking correctly while 7 underestimated between 2-4 times.

One participant overestimated with a factor of 0.5. In Group

A, the same amount of people as in group B estimated the

distance walking approximately correct, while the other 7 in

group A underestimatedwith a factor between 2-9 times with

an average of 4.5. When it comes to climbing, the distance

was prominently underestimated with a factor of 1 to 17. 2

guessed correctly, 7.5 was the average factor between the

other 7.

10

4.2 QuestionnaireOverall, the questionnaire scoring did not show any signif-

icant differences and both groups rated their responses to

the questions correspondingly to a strong sense of presence.

Some of the minor findings will in turn be presented.

Group A scored a slightly higher number than group B in the

questionnaire in regards to how natural their interactions

felt. At the same time, group A felt equally compelled in

their sense of moving as the control group. Moreover, they

showed a little more confidence in their ability to search and

survey the space (See Figure 6).

Figure 6: Questionnaire responses about natural interac-tions and compelling sense of movement

In relation to time and space, group A seemed to easier

lose track of time. They were also somewhat more confused

than the control group. Group A scored almost as high rating

as Group B in the feeling of skilfulness towards the end of

their experience (See Figure 7).

Figure 7: Questionnaire responses about track of time andconfusion

In terms of adjustment to hand controls that steered the

locomotion, responses from group A indicate minor inter-

ference from hand controls. Both groups seem to have been

somewhat distracted by hand controls or the methods of

locomotion. However, there is a slight difference in how well

users adapted to the hand controls but group A adjusted

themselves almost as quickly as group B (See Figure 8). They

also rated a marginally lower response in naturalness in

movement mechanisms.

Figure 8: Questionnaire responses about control device in-terfering

Meanwhile, Group A was somewhat more distracted in

general than group B and was almost as involved in the

virtual experience as the control group. There were fewer

moments in which users felt completely focused on their task

or the environment during their experience in Group A than

B. The groups rated equally in response to how consistent

events in the virtual world related to the real world.

4.3 InterviewAfter the qualitative data was cleaned, coded and analysed

the following concepts and themes became evident where

the two groups were similar and differed.

4.3.1 Sense of freedom. The environment was perceived as

a tight, restrictive space by 6 participants from group B and

5 from group A. They reported that the path felt narrow and

they felt that the space felt physically tight to move inside.

Two of these participants in group A described the space as

being somewhat claustrophobic. The six participants from

group B described the size and nature of the space in a neg-

ative way and three of these mentioned that they walked

differently as in more consciously, carefully and slower than

they would normally. One of these said that she needed to

squeeze tight to get around the narrow corners and "it felt

hard, I felt fat" (B9) when asked how she would describe

her experience of walking in the environment. Two of the

six participants that mentioned the size of the space also

expressed that they would have liked a bigger environment

to be able to walk freely.

Two of the five participants of Group A also shared this opin-

ion while four of the six participants felt that it was small in

11

a negative way. One participant mentioned that the tightness

of the space subtracted from the immersion compared to if it

had felt bigger. Three of them reported that the narrow space

restricted them in their walking as they felt that they "didn’t

have space to walk" (A6), "they needed to walk carefully in

that narrow space" (A1), the space "felt like I wasn’t meant

to walk there... walking made me notice how small the space

was faster" (A5). One of these described that they sensed that

they in the real physical space often turned around oneself

to get to new paths.

Other participants spoke about freedom in regards to climb-

ing as "...to be able to be everywhere. Nothing was off-limits.

A freedom to be everywhere, that empowers" (A4) and "the

feeling of freedom" (A3). In Group B, the theme was men-

tioned twice where "it felt spacious, feels like I am walk-

ing around but more freely" (B4) and by "looking upwards

confined spaces of her real-life closed apartment ceiling is

broken. I have a feeling of depth even though I know it is

only virtual." (B6).

4.3.2 Sense of exploration. Four of the six participants in

Group A that had discussed the size of the area negatively

expressed that climbing added to the space available for

them and elongated space for them to explore as climbing

"prolongs the area you have at disposal... contributed to the

exploration of space" (A6), "adds another dimension" (A1),

"made sense to be able to climb in that sort of space" (A5),

"provided a different perspective" (A3), and "added to the

room experience to be able to go there (the vertical space)

... they "escaped the very small, tightness of the space with

climbing" (A3). Another said that climbing made one "able

to move to unreachable areas... explore the area and find

secrets" (A7).

The participants in Group A expressed the connection be-

tween climbing and exploration in different ways. Some

stated that walking was favored and used for discovering

and searching while climbing was used to examine what

they could already see. These four participants stated that

with climbing they "preferred walking for searching. As the

world feels big even though it is small... I liked to experi-

ence every little corner" (A4), felt that "climbing doesn’t take

you to a new place like walking does" (A9), they discovered

through walking and "climbing makes the experience come

to a halt as I am the most immersed when I discover things...

momentum is a bit lost" (A4). Another participant said that

"it is another dimension but not much exploration because of

can see it all" and that the environment in this regard didn’t

feel as though it was meant for climbing as it was "superlin-

ear, just straight lines" (A8). However, the same participant

also said that they "loved the feeling of exploring in another

direction... with climbing could move in another dimension...

height exploration" (A8). Nonetheless, one participant expe-

rienced "more active searching when climbing to scan more

surface and it slows down the pace of progress" (A7) and

another stated that they could move "both through space

and volume with both locomotions... A feeling of freedom"

(A3). Other participants in Group A mentioned exploration

in conjunction with walking, for example, it felt "explorative

to walk and find new rooms or dead ends" (A1), "contributes

to the exploration of space (about climbing)" (A6), and they

"(with walking) wanted to find out what was in the end

which felt fantastic... great VR experience to be able to move

so because it is such a natural way of exploring" (A10).

In the control group, walking was mentioned as a way to ex-

plore in different ways. Some expressed more clearly walking

in terms of exploration like "walking there set an explorative

mood" (B2), "it was exciting to move around and look for

cubes (about walking)" (B9), "cool to walk around and explore

while taking in impressions, looking upwards" (B6) and "it

feels like you are progressing (about walking and their task)"

(B5). One participant felt differently, that "walking doesn’t

trigger that much except curiousness of what’s around the

corner" (B3).

4.3.3 Sense of motion. All ten participants in Group A dis-

close that climbing in different degrees added to their ex-

perience. As mentioned above, participants liked the possi-

bilities of exploring the vertical space that the multi-level

locomotion made available. Apart from this, the participants

mentioned other factors such it "added moments (to the

experience)" (A9), "adds the sensation of touch and helps

reinforce the existence of the environment as it shows a

concrete existence of movement" (A8), was "a positive chal-

lenge" (A10), "provides new opportunities than what you

have in real-life... felt immersed when I was climbing (A5),

"doubled the experience"(A1). Three participants in Group A

experienced difficulties with the concept of climbing. They

didn’t perceive the climbing technique as climbing. They felt

that it didn’t feel like climbing but more like they pulled the

world in different directions. On of these declared that they

experienced difficulties grasping height in the environment.

However, they also felt that it was fun the be up in the air

and "to reach different levels". This participant on one occa-

sion didn’t recognise her controllers touching the floor but

thought there was some kind of obstacle that had appeared

in the physical room when she was physically bending over.

Two participants felt that the climbing technique could with

a little more implementation be crystallised "for a bigger

experience" (A7) and "maybe not break the immersion" (A8).

Issues mentioned were fatigue in the long run, acceleration,

speed and improvements in control display relationships to

be able to reach further away more effortlessly. Four other

participants were indifferent to the method of climbing but

12

liked the experience of the benefits that came with the climb-

ing. As one of them described "its combination with walking

stands out" (A6).

Meanwhile, 6 out of the 10 participants in Group A expressed

that they thought climbing was a good complement to walk-

ing. One participant in Group A described that they could

use walking and climbing move as they liked as they com-

plemented each other well. The participant also described

the locomotions with "walking is static, it is much more

fun to use your hands than walking around" and in that

way "climbing contributed... to move both horisontally and

vertically" (A1). Another reported that they had the free-

dom to walk mid-air and climb upwards and downwards

when needed to make use of both locomotions effectively. It

was also described as "another category of movement" (A7),

"broke routine of pure self-walking folding spaces" (A8), "a

break from walking and offered variation" (A3), "fun to do

because you can’t climb like that in real-life" (A10). Another

stated that climbing was "different (to walking)" and they

would have liked to climb more all-around in their walk-

through as they would have preferred "less walking as it

corresponds to walking in real-life" (A5).

4.3.4 Naturalness. The majority of participants remarked

that walking felt natural and realistic. In Group B the loco-

motion technique was referred to as an example as it "felt

consistent and felt like walking in real-life" (B1) and "might

as well have been (walking in) a real corridor" (B7). When

answering questions about how it felt to walk two partici-

pants stated that "one doesn’t notice where one is, you are

effectively immersed" (B10) and that they "felt presence in

that space" (B6). In total, 7 participants in Group B discussed

naturalness in conjunction with walking. However, one of

these together with another not part of these 7 interviewees

reported that they sensed that they walked in circles. Mean-

while, the latter claimed that walking "felt just as immersive

as standing still" (B8). Another said that "it felt hard to walk"

(B9). Five participants in Group B said that they walked dif-

ferently, participants B2, B4, B6, B8 and B9, as they moved

carefully in the corridors and more consciously than they

would normally in real-life. Only one participant noted that

they would often walk with their hands raised to not move

into walls because it was hard to trust the ability to walk in

virtual reality.

Similarly, 8 participants in group A talked about walking

in terms of it being natural for example a "natural way of

exploring" (A10), "walking was completely intuitive and nor-

mal" (A6) and "when I moved, it was corresponding to her

steps in real-life" (A2). However, one participant that did call

walking natural also said that it didn’t feel like they could

see from their point of view but it "was more like a smooth

camera like in movies, smoother than real-life walking" (A2).

Two participants in Group A referred to climbing as natural

and realistic to some degree as it "feels relatively realistic"

(A5) and "looked realistic" (A3). One of them also noted that

it felt realistic though it was evident that he was weight-less

while two other participants felt that they were in a space

that defied physical laws and was non-dependent on physics.

One of them actively climbed less because they didn’t like the

feeling of defying physical laws. Two participants claimed

that climbing, in contrast, was unnatural and artificial with

one wanted to use her feet too for it to be more natural.

Another participant stated the unrealistic effect on the im-

mersion as "climbing contributed to the experience but took

away from the realism. I felt more immersed when I was

climbing, even though it felt less realistic" (A5). Likewise,

besides declaring the realism of climbing, A3 also stated that

"climbing gave less of a feeling of movement in the room,

which is a bit negative" (A3).

Moreover, in comparison to climbingwalkingwasmentioned

that "walking felt better than climbing because it feels con-

sistent with my actions in real-life" (A7) and "climbing didn’t

feel as natural as walking, much less natural" (A8). Also,

the former also said that the climbing mechanics was "not

hard to use or understand.. no skills were required" (A8).

Meanwhile, four others meant that climbing was something

that you needed to somewhat learn and adjust yourself to

and that in a way provided a positive challenge for them.

Another reported that the nature of the climbing mechanism

functioned differently than what they had expected since

they had previous experience with a climbing VR-game.

4.3.5 Physiological responses. Three out of the ten partici-

pants of Group A reported feelings of losing or starting to

lose their balance and fear of heights while one participant

in Group B experienced slight motion sickness when they

felt that they often turned around their own axis when they

were walking in the environment.

Four users in Group B felt that the environment seemed to

shift behind them as new cubes appeared when they revisited

already traversed areas whereas in group A only two users

appeared to believe that the environment always shifted and

introduced new rooms all the time. One participant besides

these suspected that the space was shifting behind them but

was unsure.

4.3.6 Limitations. Many of the participants in both groups,

8 of Group A and 6 in Group B, reported to a varying de-

gree that they were restricted by their physical area as the

safety grid was shown sometimes or always. Often, objects

in the room such as lamps, furniture, ceiling and pets were

mentioned to be obstacles. Some participants expressed that

the immersion was taken away from the reappearing safety

grids and the objects in the physical space and distracted

them from their experience.

13

In Group A, some participants also accidentally move the

whole environment horisontally while they were climbing

which resulted in the environment having being moved out-

side of their play area. In some cases, participants managed

to break the impossible room algorithms which sometimes

resulted in the user exiting the walkthrough.

Moreover, almost every user perceived the abstract, black-

and-white, sterile environment as confusing as they often

reported problems with judging distances, heights and dif-

ferences between objects and walls. The screen recordings

of their walkthrough tell us that many participants missed

cubes high up in Group A. Moreover, the majority of users in

both groups missed cubes clustered at the same places some-

times. Some users did not reach the end of the walkthrough,

failing to explore the whole space.

Lastly, a number of participants from both groups mentioned

that they could be thrown sometimes when they attempted

to navigate in the impossible space. Some participants men-

tioned the abstract nature or the nature of the impossible

space as a possible reason for them losing their sense of di-

rection. Half of the participants in the control group were

lost at some point in their walkthrough and 2 participants

in Group A reported that they had difficulties navigating to

some degree. One of these claimed that they always climbed

down all the whole way to the floor to not get lost in the

space.

4.3.7 Summary of emotions. The users were asked to sum-

marise and describe their experience with three words with

a focus on emotions, impressions and experience. This is rep-

resented below with a 2D word map where the center holds

responses that most people had described their experiences

and also corresponds to bigger font sizes. The fewer that said

a certain word, further away from the center and font size it

has. Green represents a connection with positive emotion,

red a negative emotion and yellow where the user described

that is was neither positive nor negative. As shown, Group

A (See Figure 9) chose a greater amount of words that rep-

resented a positive emotion than group B (See Figure 10).

Group B statistically more often described their experience

with negative emotions. They also chose more diverse words

than Group A while Group A chose somewhat more neutral

words.

5 DISCUSSION5.1 Time and distance estimationsThe probable reason for the lack of major differences in time

estimation by the users is probably due to the software im-

plementation of the time calculations. Preferably, a more

accurate time measurement would have been implemented

after the pilot tests. If this had been the case, more differ-

ences in the time spent on climbing and walking would have

Figure 9: 2D word map over the responses from Group A.The center holds words that were chosen on most occasions.The font size also corresponds to the number of times it wasused to describe the experience. Green and red colors repre-sent a positive or negative emotional connection while yel-low represents indifference.

Figure 10: 2D word map over the responses from Group B.

been detected. Also, since group A needed to execute more

operations than group B in order to complete their task they

would naturally spend more time on both walking and climb-

ing. In that way, group B could have had an advantage when

it comes to keeping track of time since they were in the

environment for a shorter period of time.

Interestingly, the underestimations of walking and climb-

ing in both groups contrast with prior studies in distance

estimations. Previous work has not investigated this in com-

pressed immersive environments such as impossible spaces.

Hence, the underestimations could possibly be due to the

compelling nature of impossible spaces. The significant un-

derestimation of the distance in climbing in group A could

potentially be an unforeseen benefit of vertical navigation

in impossible spaces which further research could investi-

gate. This could also be due to the longer time spent in the

environment for group A compared to group B which could

also explain the difference in underestimation between the

groups where group A tended to underestimate the walking

distance slightly more than group B.

14

5.2 QuestionnaireBecause the results from the questionnaires from both groups

show no significant differences in the majority of the re-

sponses, this might indicate that there was no major differ-

ence in the two group’s experiences from what the ques-

tionnaire highlighted. That is to say, the questionnaire could

not be used to derive any conclusions in the difference be-

tween the two group’s experiences on its own based upon

the questionnaire solely. More generally, both groups scored

high results in the questionnaire which points to that both

environments show a high level of immersion. As Group A

scored slightly higher or as high as Group B in regards to nat-

uralness, searching and sense of moving could possibly mean

that the environment walkthrough for Group A showed a tad

higher level of presence. At the same time, Group A scored

higher than Group B in the sense of losing track of time and

confusion. The scores that dealt with control devices and

climbing mechanisms were somewhat worse in Group A and

the level of concentration on the assigned task was scored

equally between the groups.

Naturally, Group A would score differently to Group B in ad-

justment to hand controls and its interference as the former

didn’t use any buttons of the hand controls or the climbing

mechanisms that go with it. Surprisingly, the fact that Group

A was as concentrated on their task could show that the

climbing didn’t distract from the experience. In this way,

Group A was in their involvement as concentrated as Group

B in terms of emotional immersion.

Possibly, Group A could have scored high in aspects of nat-

uralness, searching and sense of movement as they would

take a longer time to execute their task than Group B. In that

way, they would spend a longer time in the environment and

it would naturally become a longer experience that could

imply higher immersion. Interestingly, Group A did however

underestimate their time spent on climbing as was shown

in 4.2 which confirms that they did lose track of time. This

could imply a disconnect from the real world in terms of

spatial immersion.

5.3 InterviewWhen comparing the experiences of the two groups of the

space, more generally one can’t draw any conclusions about

that there were any differences to how the participants per-

ceived the space as an almost equals part of participants

in both groups talked about the space in negative terms.

However, the fact that two participants in Group A and one

in Group B did express themselves in terms of freedom di-

rectly in conjunction with the vertical space indicates that it

could be the vertical space brought about feelings of freedom.

Naturally, the vertical space in the environment was much

bigger than the horistonal but it still shows a potential con-

nection to the participant’s experience in terms of a feeling

of freedom of vertical space. Although, experiencing a sense

of freedom and spaciousness is in its own not necessarily

more immersive than the opposite, to not feel freedom or

claustrophobic feelings. Feelings of being in a tight space

could of course be just as believable and convincing in an im-

mersive sense for any user. Nonetheless, these results could

point to Group A having a more positive experience than

Group B. The connection between the users and the feeling

of freedom can be viewed as a sense of spatial immersion.

As both groups displayed a degree of spatial immersion in

this sense, it is notable that users in Group A seem to be

immersed more positively.

More interestingly, the context of how the sense of free-

dom was discussed could yield more insights. As four out

of the six participants in Group A that had talked about the

tightness of the space implied that they with climbing had

more area to explore at their disposal. This indicates, as one

participant also described it as, Group A could in a way es-

cape the claustrophobic side of the impossible spaces through

vertical navigation. In this sense, climbing contributed to

their experience by providing users with a vertical space for

them to move in. The fact that the users not only as Group

B experienced the tightness and a degree of claustrophobia,

but they could through climbing make use of another space

to reduce those feelings implies a level of spatial immersion.

In fairness, as there were four participants that expressed the

vertical locomotion in terms of as an escape or relief from

the tight space, not all participants in Group A might have

felt that the vertical space that the locomotion made avail-

able were as convincing. Nevertheless, the fact that users

experience the feeling of freedom and were aware of the

space points to the fact that the space would be somewhat

believable in its existence. If the climbing on its own wasn’t

compelling at all, these users would not have felt that they

could escape from the horisontal space. This does imply that

these participants experience spatial immersion.

Exploration-wise, the majority of participants in group A

preferred walking for searching. Clearly, participants from

both groups seem to have been more involved when walking

which suggests that they all experience a degree of emotional

immersion as they wanted to know what was next and used

walking to progress in their task. In that way, walking pro-

vided a narrative for most participants while climbing was

perceived as halting their feeling of a narrative. Interestingly

though is that some participants still enjoyed climbing. Some

participants expressed that they appreciated the examining

part of being able to climb, active searching and moving in a

so-called "another dimension". This could indicate that these

particular participants felt spatial immersion and emotional

immersion as climbing provided them with an experience of

15

moving vertically, brought about feeling about that and also

contributed to their narrative.

When looking at climbing in terms of a sense of motion,

it is evident that the majority of the participants felt that

climbing on its own was not believable nor convincing as the

method on its own was not perceived as natural. Nonethe-

less, as mentioned above the exploration or examination of

the vertical space that came as a consequence of the locomo-

tion was compelling. As some participants noted that they

didn’t even experience the climbing technique as climbing

the locomotion implementation was in practice too artificial

for them. All participants agreed that climbing contributed

to their experience, while it was not gripping in its own. One

must now keep in mind that this is based on this sole im-

plementation of climbing and there is possible that different

tweaks and alteration to this technique would yield different

results. The participants themselves stated that the technique

could be further developed. Possibly, this prototype could

have been a minimal cue in its implementation as it fails to

deliver strong immersive feelings, but only some. Besides

the nature of moving in the vertical axis, participants did

experience a higher sense of touch as walls were reinforced

in their existence, provided a new sense of motion while also

doubled their experience. An illustrative example of this is

when one participant did not even recognise the floor with

her controllers which seems as though she wasn’t aware of

all of her physical body. This shows again signs of spatial

immersion of actually being there in the room, leaving the

physical real-life behind.

Strikingly, 6 out of 10 participants agreed that climbing was

a good complement to walking. This shows that even though

most of the participants did not relish the actual sense of

motion, they would not reject the idea as they found that

climbing was dynamic to walking in the impossible space.

Some participants tended to use walking and climbing more

complementary, alternating them to effectively execute their

experimental task. The combination of walking and climb-

ing seems to have been stimulating in some sense and pro-

vided some users with means of progress as they developed

skills for more effectively using the locomotions at hand.

This points to a mental incentive to both learn to combine

two techniques more competently. The action of climbing

is rhythm-based in terms of visual stimuli and due to the

fact that participants could describe it as breaking the rou-

tine of walking is seems that there are elements of tactical

immersion. Walking and climbing are both repetitive and

creates a natural rhythmic motion. In this case, walking was

not the only compelling locomotion but climbing was also

appreciated.

The four participants in group A that explained climbing as

something they needed to learn in order to operate more

skillfully is another sign of immersion. The process of learn-

ing and master the locomotion could be seen as mentally

stimulating which indicates cognitive immersion. More im-

portantly, this element of a challenge was seen as positive

by the user and not overwhelming. This aspect attests to

cognitive immersion in the form of mentally motivating.

The fact that fewer participants in Group A than Group B

thought the static environment was ever-changing around

them which it wasn’t might suggest that participants in

Group A were less overwhelmed of the complexity of the im-

possible space. In this case, climbing might have helped with

the sense of navigation. However, the questionnaire showed

that Group A was slightly more confused than Group B. This

would contradict the observation but it could also be possible

the confusion in the questionnaire was mostly due to the

mechanics of the climbing as the question was not especially

aimed at the confusion in terms of navigation. In this regard,

no conclusions can be drawn but would need further studies

and investigations.

The fact that many more participants in Group B than in

Group A reported that they walked differently as in more

carefully, consciously and sometimes slower than they would

in real-life is thought-provoking. Clearly, most parts of group

A perceived walking as natural while climbing not natural

but interestingly they did not report any limitations specific

to walking. Of course, most participants struggled with the

play area being too small for its purpose but Group A seems

to have been more unrestricted in their walking while half

of group B was. Somehow, Group A tended to walk more

naturally than Group B in this sense. Possibly, this could

be due to chance or maybe that Group A found it easier

to place trust in the environment. As they exhibited more

comfort than Group B, they could have felt safer in their sur-

roundings. If that would be the case, their experience would

again prove more positive than Group B. Feelings of trust

and safety could in extent be connected with involvement as

well as spatial awareness in regards to emotional and spatial

immersion.

The matter of realism is complex. As two participants stated

that climbing was realistic, one participant noted that he felt

more immersed while climbing even though it took away

from the realism while other participants viewed climbing

as unnatural and one even stated that it decreases the sense

of presence of being there in the room, the results show

mixed opinions of immersion. As studies have argued, real-

ism could be less important than other measures and it does

not provide for a good measurement of immersion when the

virtual environment is not based on reality. As the impossible

space is something out of the ordinary and could not exist in

real-life as you can’t draw it or map it, no such environment

resembles any real-life contexts. Granted, there are floors,

walls and roof but the space in itself is extraordinary and

16

only possible to experience virtually. Therefore, one can ar-

gue that realism does not entail immersion in this particular

situation. The whole point with virtual reality is not to just

depict a real-life environment with no difference to real life

but to also be able to expand the limits of the concept of vir-

tual realities. The curious thing about virtual reality is that

there are no limits to the environment and that one could

create compelling, fascinating and breathtaking abstract en-

vironments that one has never experienced before. Therefore,

research should not limit itself to realistically capture a real-

istic landscape and project it into a virtual reality context but

broaden our horisons of what is possible in an unimaginable

world that defies every one of the worldly restrictions of our

world. In extension, physical laws such as gravity are also

a matter of realism. In a world without real-life restrictions,

gravity might not either give a good measurement of immer-

sion. Of course, gravity is closely connected to climbing as

participants drew on the fact that they experience climbing

as unrealistic and unnatural due to being weightless. This

could also have something to do with immersion being rein-

forced when subjects relate to their virtual avatar. As one of

the participants talked about being uncomfortable breaking

laws of gravity as well as the possibility of adding avatar feet

this could show that the problem is not with gravity itself

but the need of relating more to the virtual avatar which

previous studies have shown is an important factor of im-

mersion. In this way, due to the extraordinary nature of the

virtual environment, the weightless property of simulating

this technique of climbing is not what will immerse the user

but the representation of avatar. In the definition of immer-

sion, representational avatars could perhaps be included in

both emotional and spatial immersion as it would reinforce

presence and personal investment.

Emotional immersion is more present in the 2Dwordmaps of

Group A than Group B. In comparison, as Group A described

their experience more positively with engaging and involve-

ment while Group B more often described their experience

in more negative emotions Group A was more emotionally

immersed than Group B in a positive sense.

6 CONCLUSIONSThe significant underestimation of distance climbed contra-

dicts previous studies. This could imply that users lose track

of time more easily in the context of impossible spaces in

regards to climbing but this finding needs further studies

to confirm this effect. The presence questionnaire showed

that the experience of climbing in an impossible space is

an immersive experience and shows little differences to the

same environment using only natural locomotion. Users also

lose track of time which would indicate a level of spatial

immersion. Their ability to concentrate just as well as the

control group points to a degree of emotional immersion.

This could possibly be explained by the longer time spent

in the environment by Group A. Interviews showed that

there were no difference in how they perceived the space, in

this case, an equal amount of users in the groups described

the space in negative terms. However, some climbers ex-

pressed a reduction of feelings of claustrophobia and instead

of feelings of freedom by the use of vertical locomotion. The

escape from the tightness of the space that is made possi-

ble by climbing suggests a convincing feeling of the space

that could be interpreted as spatial immersion. Also, these

climbers seem to have been more positively immersed here

than the control group which shows lesser signs of feelings

of freedom and experience made through vertical space. Only

some participants experience emotional immersion in the

form of narrative while climbing in comparison to walking

while walking provided a stronger narrative. The climbing

technique was locomotion-wise perceived as mostly unnatu-

ral and artificial. Here, many possible changes and tweaks

could be further investigated to crystallise a reliable and

competent climbing locomotion. Despite its unnaturalness,

all climbers felt that climbing contributed to their virtual

reality experience and a little more than half agreed that

climbing and walking complemented each other. This com-

plementing aspect of combining walking and climbing seems

to have positively as well as mentally stimulated the users

to some extent in terms of progress, effectively executing

tasks and challenges. Climbers exhibited more sense of se-

curity and trust in walking in the environment than the

control group which implies emotional and spatial immer-

sion. Tactile immersion seems to have occurred when used

in combination with walking. Realism may not be a reliable

measurement to be used to describe immersion as impossi-

ble spaces do not resemble real-life situations as the results

indicate levels of immersion in different aspects even though

climbing as a locomotion technique was artificial. Weight-

lessness and defying laws of nature could therefore be more

closely connected to virtual avatar representation in terms of

emotional and spatial immersion of "being there" and being

invested. In this way, this particular climbing locomotion

in this environment displays prominently spatial and emo-

tional immersion, partly cognitive immersion and to some

degree tactical immersion. When asked to summarise their

experience, climbers depict their experience more positively

than the control group which points to a better experience

for climbers which demonstrates Group A being more posi-

tively immersed. This could be due to a number of factors

like the longer time spent in the environment, etc. but could

prove that vertical navigation in terms of climbing enhances

virtual reality experiences in impossible spaces if confirmed

with future studies. This experiment might be touching the

limits of minimal cues of the technique of climbing and the

17

results show that there is much to gain and experience in

advancing in vertical locomotion.

6.1 Method criticismOne must keep in mind that there could be many factors that

would affect the results of the user studies. Besides the cir-

cumstances mentioned, the level of experience with both VR

and impossible spaces would have affected the experience.

Prior encounters with this effect both users novel to the tech-

nique as well as more experienced participants. Moreover,

personal preferences and cultural factors could play a role

in perception. As the study’s investigation had in total of

20 participants, there are also risks of missing out on voices

that could have provided different insights. Subsequently,

the study’s findings would need to be confirmed by further

studies. Additionally, there are more circumstantial factors

that could have influenced. For instance, one could now in

hindsight have reduced and make questionnaire questions

more concrete. These could have been more accurate for the

purpose of the study and be less vulnerable to ambiguity.

Also, interviewees could have been asked their opinion on

the sense of freedom, exploration, motion and naturalness if

they themselves didn’t touch upon the subject. It is possible

that more participants could have agreed with some of the

views described but that it didn’t come up during their in-

terview. A second iteration could have picked up opinions

that were missed in this study. If the scope of the study had

been bigger, a second or even third iteration of user studies

would have been preferable to also tweak the environment

as some problematic aspects of the study could have been

altered to strive for further results.

Clearly, as participants from both groups reported negative

effects of the size of the impossible space this is a parameter

that could have affected the participants sense of freedom in

general. In its own, investigating a bigger impossible space

would be interesting as to see if it would affect the experience

of the participants in a immersive regard. Moreover, if the

tests had been performed in a way so that every participant

would have had a larger play area it could have affected the

experience as no safety grids, guardian offsets or distractions

would have interfered with their sense of freedom. As of

now, the sense of freedom could largely have depended on

each individual’s play area instead of the environment they

tested out.

Similarly, as many of the participants remarked on the ab-

stract nature of the environment and struggles to make out

objects and distances. If the environment were less sterile

and extremely abstract user could perhaps have been less

confused. More importantly, as users expressed that the ap-

pearance and lack of art distracted them and took away from

their immersion the abstraction of the environment could

have more likely hindered the study in immersion rather

than helped. A better middle ground in regards to environ-

mental art and maybe using hand avatar and not controllers

could have been useful.

Moreover, during other circumstances the test would have

taken place face to face. This would have helped in order

to make sure participants finished their task before exiting,

less breakage of the environment and could have asserted

that the user would have a sufficient play area during their

walkthrough. Meeting physically would also result in better

audio recordings as due to software issues and sound quality,

the recorded material was at times muffled. The note taking

from the ongoing discussions was more reliant in this case

but audio recordings face to face would have been ideal.

Lastly, errors can always occur due to the human factors in

regards to manual coding in the qualitative data analysis.

6.2 Future workFirstly, it would be useful to further tweak and excel in de-

veloping a more stable and reliable climbing technique for

further testing in the same situation with impossible spaces.

Notable, testing climbing techniques with impossible spaces

where climbing can take users to new rooms could give new

insight and might confirm the legitimacy of the findings of

this study. Other methods such as think-aloud might high-

light new aspects. Also, other vertical locomotions would be

interesting to compare to climbing in this setting as swim-

ming, walking up stairs, elevators, or new ideas on how to

solve for vertical locomotion. We are in need of gaining a bet-

ter understanding of user experiences in impossible spaces

and its aspects of immersion for making virtual reality more

accessible and usable. These potential studies could prove

useful for defining its limitations and how the experience can

be extended. Since locomotion is still an issue to be solved in

virtual reality, experimenting and testing within this area are

much needed. Research into impossible spaces in conjunc-

tion with simulating vertical locomotion would gain insights

in creating future virtual realities.

7 ACKNOWLEDGEMENTSI owe many people thanks for making my thesis possible.

Firstly, my supervisor Linnéa Granlund at Resolution Games

has been a great help and a good listener. Secondly, I’d like

to give a warm thank you to Björn Thuresson for being my

supervisor at KTH always giving me competent and engag-

ing advice in both academics and life. Last but not least, the

very kind people who volunteered to take part in my study.

In these strange times, each and everyone that has helped

me has played a vital role in my thesis. In particular, I’d liked

to thank my family for being there and being patient in my

quarantine thesising. The thesis was executed in associa-

tion with Resolution Games which I would like to thank for

giving me this great opportunity.

18

REFERENCES[1] Immersion, 2020. Last accessed 2 Jun 2020.

[2] Asjad, N. S., Adams, H., Paris, R., and Bodenheimer, B. Perception

of height in virtual reality: a study of climbing stairs. In Proceedings ofthe 15th ACM Symposium on Applied Perception (2018), pp. 1–8.

[3] Bjork, S., and Holopainen, J. Patterns in game design, vol. 11. CharlesRiver Media Hingham, 2005.

[4] Boletsis, C. The new era of virtual reality locomotion: a systematic

literature review of techniques and a proposed typology. MultimodalTechnologies and Interaction 1, 4 (2017), 24.

[5] Bowman, D., Kruijff, E., LaViola Jr, J. J., and Poupyrev, I. P. 3D Userinterfaces: theory and practice, CourseSmart eTextbook. Addison-Wesley,

2004.

[6] Bowman, D. A., and McMahan, R. P. Virtual reality: how much

immersion is enough? Computer 40, 7 (2007), 36–43.[7] Bozgeyikli, E., Raij, A., Katkoori, S., and Dubey, R. Point & teleport

locomotion technique for virtual reality. In Proceedings of the 2016Annual Symposium on Computer-Human Interaction in Play (2016),

pp. 205–216.

[8] Brooks, F. P. What’s real about virtual reality? IEEE Computer graphicsand applications 19, 6 (1999), 16–27.

[9] Bruder, G., Lubos, P., and Steinicke, F. Cognitive resource demands

of redirected walking. IEEE transactions on visualization and computergraphics 21, 4 (2015), 539–544.

[10] Cheng, L.-P., Ofek, E., Holz, C., and Wilson, A. D. Vroamer: Gener-

ating on-the-fly vr experiences while walking inside large, unknown

real-world building environments. In 2019 IEEE Conference on VirtualReality and 3D User Interfaces (VR) (2019), IEEE, pp. 359–366.

[11] Darken, R. P., Cockayne, W. R., and Carmein, D. The omni-

directional treadmill: a locomotion device for virtual worlds. In Pro-ceedings of the 10th annual ACM symposium on User interface softwareand technology (1997), pp. 213–221.

[12] Dean, D., Millward, J., Mulligan, L., Saleh, I., Wise, C., and Hig-

gins, G. Evaluating alternative input techniques for building and

construction vr training. In 2018 IEEE International Conference onTeaching, Assessment, and Learning for Engineering (TALE) (2018), IEEE,pp. 1001–1004.

[13] Dong, Z.-C., Fu, X.-M., Zhang, C., Wu, K., and Liu, L. Smooth as-

sembled mappings for large-scale real walking. ACM Transactions onGraphics (TOG) 36, 6 (2017), 1–13.

[14] Feasel, J., Whitton, M. C., Kassler, L., Brooks, F. P., and Lewek,

M. D. The integrated virtual environment rehabilitation treadmill

system. IEEE Transactions on Neural Systems and Rehabilitation Engi-neering 19, 3 (2011), 290–297.

[15] Ferracani, A., Pezzatini, D., Bianchini, J., Biscini, G., and

Del Bimbo, A. Locomotion by natural gestures for immersive vir-

tual environments. In Proceedings of the 1st international workshop onmultimedia alternate realities (2016), pp. 21–24.

[16] Fisher, J. A., Garg, A., Singh, K. P., and Wang, W. Designing inten-

tional impossible spaces in virtual reality narratives: A case study. In

2017 IEEE Virtual Reality (VR) (2017), IEEE, pp. 379–380.[17] Freina, L., and Ott, M. A literature review on immersive virtual real-

ity in education: state of the art and perspectives. In The InternationalScientific Conference eLearning and Software for Education (2015), vol. 1,pp. 10–1007.

[18] Garg, A., Fisher, J. A., Wang, W., and Singh, K. P. Ares: An applica-

tion of impossible spaces for natural locomotion in vr. In Proceedingsof the 2017 CHI Conference Extended Abstracts on Human Factors inComputing Systems (2017), pp. 218–221.

[19] Iwata, H. The torus treadmill: Realizing locomotion in ves. IEEEComputer Graphics and Applications 19, 6 (1999), 30–35.

[20] Iwata, H., Yano, H., Fukushima, H., and Noma, H. Circulafloor

[locomotion interface]. IEEE Computer Graphics and Applications 25, 1(2005), 64–67.

[21] Iwata, H., Yano, H., and Nakaizumi, F. Gait master: A versatile

locomotion interface for uneven virtual terrain. In Proceedings IEEEVirtual Reality 2001 (2001), IEEE, pp. 131–137.

[22] Iwata, H., Yano, H., and Tomiyoshi, M. String walker. In ACMSIGGRAPH 2007 emerging technologies. 2007, pp. 20–es.

[23] Kamboj, V., Bhuyan, T., and S. Pillai, J. Vertical locomotion in vr

using full body gestures. In 25th ACM Symposium on Virtual RealitySoftware and Technology (2019), pp. 1–2.

[24] Kassler, L., Feasel, J., Lewek, M. D., Brooks Jr, F. P., and Whitton,

M. C. Matching actual treadmill walking speed and visually perceived

walking speed in a projection virtual environment. In Proceedings ofthe 7th Symposium on Applied Perception in Graphics and Visualization(2010), pp. 161–161.

[25] Lai, C., McMahan, R. P., and Hall, J. March-and-reach: A realis-

tic ladder climbing technique. In 2015 IEEE Symposium on 3D UserInterfaces (3DUI) (2015), IEEE, pp. 15–18.

[26] Langbehn, E., Lubos, P., and Steinicke, F. Redirected spaces: Going

beyond borders. In 2018 IEEE Conference on Virtual Reality and 3DUser Interfaces (VR) (2018), IEEE, pp. 767–768.

[27] McCullough, M., Xu, H., Michelson, J., Jackoski, M., Pease, W.,

Cobb, W., Kalescky, W., Ladd, J., and Williams, B. Myo arm: swing-

ing to explore a ve. In Proceedings of the ACM SIGGRAPH Symposiumon Applied Perception (2015), pp. 107–113.

[28] Medina, E., Fruland, R., and Weghorst, S. Virtusphere: Walking in

a human size vr “hamster ball”. In Proceedings of the Human Factors andErgonomics Society Annual Meeting (2008), vol. 52, SAGE Publications

Sage CA: Los Angeles, CA, pp. 2102–2106.

[29] Nabiyouni, M., Saktheeswaran, A., Bowman, D. A., and Karanth,

A. Comparing the performance of natural, semi-natural, and non-

natural locomotion techniques in virtual reality. In 2015 IEEE Sympo-sium on 3D User Interfaces (3DUI) (2015), IEEE, pp. 3–10.

[30] Nagao, R., Matsumoto, K., Narumi, T., Tanikawa, T., and Hirose,

M. Walking up virtual stairs based on visuo-haptic interaction. In

ACM SIGGRAPH 2017 Posters. 2017, pp. 1–2.[31] Nagao, R., Matsumoto, K., Narumi, T., Tanikawa, T., and Hirose, M.

Ascending and descending in virtual reality: Simple and safe system

using passive haptics. IEEE transactions on visualization and computergraphics 24, 4 (2018), 1584–1593.

[32] Nigatu, T. Qualitative data analysis, 2009. Last accessed 29 May 2020.

[33] Nilsson, N. C., Serafin, S., and Nordahl, R. The perceived natural-

ness of virtual locomotion methods devoid of explicit leg movements.

In Proceedings of Motion on Games. 2013, pp. 155–164.[34] Nilsson, N. C., Serafin, S., Steinicke, F., and Nordahl, R. Natural

walking in virtual reality: A review. Computers in Entertainment (CIE)16, 2 (2018), 1–22.

[35] Noma, H. Design for locomotion interface in a large scale virtual

environment. ATLAS: ATR Locomotion Interface for Active Self Motion64 (1998), 111–118.

[36] Peck, T. C., Fuchs, H., andWhitton,M. C. Evaluation of reorientation

techniques and distractors for walking in large virtual environments.

IEEE Transactions on Visualization and Computer Graphics 15, 3 (2009),383–394.

[37] Peck, T. C., Fuchs, H., and Whitton, M. C. Improved redirection

with distractors: A large-scale-real-walking locomotion interface and

its effect on navigation in virtual environments. In 2010 IEEE VirtualReality Conference (VR) (2010), IEEE, pp. 35–38.

[38] Powell, W., Stevens, B., Hand, S., and Simmonds, M. Blurring the

boundaries: The perception of visual gain in treadmill-mediated virtual

environments. In 3rd IEEE VR 2011 Workshop on Perceptual Illusions in

19

Virtual Environments (2011).[39] Razzaqe, S., Kohn, Z., and Whitton, M. C. Redirected walking.

Citeseer, 2005.

[40] Ribo, M., Pinz, A., and Fuhrmann, A. L. A new optical tracking

system for virtual and augmented reality applications. In IMTC 2001.Proceedings of the 18th IEEE Instrumentation and Measurement Technol-ogy Conference. Rediscovering Measurement in the Age of Informatics(Cat. No. 01CH 37188) (2001), vol. 3, IEEE, pp. 1932–1936.

[41] Rolland, J. P., Davis, L. D., and Baillot, Y. A survey of tracking

technologies for virtual environments. In Fundamentals of wearablecomputers and augmented reality. CRC Press, 2001, pp. 83–128.

[42] Sanchez-Vives, M. V., and Slater,M. From presence to consciousness

through virtual reality. Nature Reviews Neuroscience 6, 4 (2005), 332–339.

[43] Schwind, V., Knierim, P., Haas, N., and Henze, N. Using presence

questionnaires in virtual reality. In Proceedings of the 2019 CHI Con-ference on Human Factors in Computing Systems (New York, NY, USA,

2019), CHI ’19, Association for Computing Machinery.

[44] Slater, M. A note on presence terminology. Presence connect 3, 3(2003), 1–5.

[45] Slater, M., Usoh, M., and Steed, A. Taking steps: the influence of a

walking technique on presence in virtual reality. ACM Transactions onComputer-Human Interaction (TOCHI) 2, 3 (1995), 201–219.

[46] Souman, J. L., Giordano, P. R., Schwaiger, M., Frissen, I., Thümmel,

T., Ulbrich, H., Luca, A. D., Bülthoff, H. H., and Ernst, M. O.

Cyberwalk: Enabling unconstrained omnidirectional walking through

virtual environments. ACM Transactions on Applied Perception (TAP) 8,4 (2008), 1–22.

[47] Suma, E. A., Azmandian, M., Grechkin, T., Phan, T., and Bolas, M.

Making small spaces feel large: infinite walking in virtual reality. In

ACM SIGGRAPH 2015 Emerging Technologies. 2015, pp. 1–1.[48] Suma, E. A., Clark, S., Krum, D., Finkelstein, S., Bolas, M., and

Warte, Z. Leveraging change blindness for redirection in virtual

environments. In 2011 IEEE Virtual Reality Conference (2011), IEEE,pp. 159–166.

[49] Suma, E. A., Lipps, Z., Finkelstein, S., Krum, D. M., and Bolas, M. Im-

possible spaces: Maximizing natural walking in virtual environments

with self-overlapping architecture. IEEE Transactions on Visualizationand Computer Graphics 18, 4 (2012), 555–564.

[50] Sun, Q., Wei, L.-Y., and Kaufman, A. Mapping virtual and physical

reality. ACM Transactions on Graphics (TOG) 35, 4 (2016), 1–12.[51] Sutherland, I. E. The ultimate display. Multimedia: From Wagner to

virtual reality 1 (1965).[52] Takala, T. M., and Matveinen, M. Full body interaction in virtual

reality with affordable hardware. In 2014 IEEE Virtual Reality (VR)(2014), IEEE, pp. 157–157.

[53] Templeman, J. N., Denbrook, P. S., and Sibert, L. E. Virtual loco-

motion: Walking in place through virtual environments. Presence 8, 6(1999), 598–617.

[54] Usoh, M., Arthur, K., Whitton, M. C., Bastos, R., Steed, A., Slater,

M., and Brooks Jr, F. P. Walking> walking-in-place> flying, in virtual

environments. In Proceedings of the 26th annual conference on Computergraphics and interactive techniques (1999), pp. 359–364.

[55] Vasylevska, K., and Kaufmann, H. Towards efficient spatial compres-

sion in self-overlapping virtual environments. In 2017 IEEE Symposiumon 3D User Interfaces (3DUI) (2017), IEEE, pp. 12–21.

[56] Vasylevska, K., Kaufmann, H., Bolas, M., and Suma, E. A. Flexible

spaces: Dynamic layout generation for infinite walking in virtual envi-

ronments. In 2013 IEEE Symposium on 3D User Interfaces (3DUI) (2013),IEEE, pp. 39–42.

[57] Vasylevska, K., Kaufmann, H., and Khrystyna, V. Influence of

vertical navigation metaphors on presence. In Challenging Presence-Proceedings of 15th International Conference on Presence (ISPR 2014)(2014), pp. 205–212.

[58] Wilson, P. T., Kalescky, W., MacLaughlin, A., and Williams, B. Vr

locomotion: walking> walking in place> arm swinging. In Proceedingsof the 15th ACM SIGGRAPH Conference on Virtual-Reality Continuumand Its Applications in Industry-Volume 1 (2016), pp. 243–249.

[59] Witmer, B. G., Jerome, C. J., and Singer, M. J. The factor struc-

ture of the presence questionnaire. Presence: Teleoperators & VirtualEnvironments 14, 3 (2005), 298–312.

[60] Witmer, B. G., and Singer, M. J. Measuring presence in virtual

environments: A presence questionnaire. Presence 7, 3 (1998), 225–240.[61] Yakovlev, K., Baskin, E., and Hramoin, I. Grid-based angle-

constrained path planning. In Joint German/Austrian Conference onArtificial Intelligence (Künstliche Intelligenz) (2015), Springer, pp. 208–221.

20

TRITA -EECS-EX-2020:489

www.kth.se