Low – Cost Devices Used in Virtual Reality Exposure Therapy

Available online at www.sciencedirect.com

ScienceDirect Procedia Computer Science 104 (2017) 445 – 451

ICTE 2016, December 2016, Riga, Latvia

Low – Cost Devices Used in Virtual Reality Exposure Therapy Pawel Buna,*, Filip Gorskia, Damian Grajewskia, Radoslaw Wichniareka, Przemyslaw Zawadzkia a

PoznaĔ University of Technology, Piotrowo 3 STR, 60-965 Poznan, Poland

Abstract The Virtual Reality technology is nowadays dynamically developed, thanks to appearance of low-cost devices and interest by large companies related to entertainment, communication and visualization. It is especially important in medicine, as it allows a much wider access to tools such as Virtual Reality Exposure Therapy. The paper presents possibilities of using low-cost VR devices in curing phobias by exposure to a stress-generating factor in an immersive virtual environment. Several use scenarios are presented for a simple application aimed at exposing a patient to fear of heights. A test group consisted of healthy individuals. To evaluate level of immersion and fear caused by the application, a heart rate monitor was used, to record heartbeat in real time. © Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2017 2016The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee the scientific committee of the international conference; ICTE 2016. Peer-review under responsibility of organizing committee of theofscientific committee of the international conference; ICTE 2016 Keywords: Virtual reality; Low – cost devices; Virtual reality exposure therapy

1. Introduction During the recent years, the Virtual Reality (VR) technology developed significantly. The VR applications, starting from a level of simple graphic applications made for entertainment and studies, now are used extensively in many professional branches. Virtual Reality can be used as specialized engineering tool1,2, for medical education3,4, engineering education5,6 or advanced training and simulation systems7. One of the frequently mentioned uses of VR is treatment of psychological conditions, such as phobias and anxieties, by means of exposure, which is known as the VRET – Virtual Reality Exposure Therapy8. There are many cases of successful use of such therapeutic tools, for example in treatment of acrophobia9 and post-traumatic stress disorder10.

* Corresponding author. Tel.: +48 61 665 2708; fax: +48 61 665 2774. E-mail address: [email protected]

1877-0509 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the scientific committee of the international conference; ICTE 2016 doi:10.1016/j.procs.2017.01.158

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To increase efficiency of a therapy, it is necessary to increase immersion level, in order to induce the feeling of presence and – as a result – anxiety needed for therapeutic results11. Immersion, understood as a feeling of being physically present in a non-physical world, can be expanded using appropriate tracking and vision systems12,13, as well as haptic devices14, allowing to touch and feel virtual objects. Up to this point, a relevant limitation for development of VR applications for wider audience was price of certain peripheral device for interaction with the virtual environment, well beyond capabilities of even medium companies, let alone individual users. Development of the new batch of so-called low-cost devices (started by the Oculus Rift DK1 device), as well as growing interest by large electronic entertainment companies (such as Samsung, Microsoft etc.) leads to increase availability and popularity of VR technology. This translates into using it in disciplines, where potential is large, but potential use was scarce – such as the VRET. An example of this application of the low-cost devices is the “Be Fearless” program introduced by the Samsung company15, aimed for use by individual users to help them overcome certain anxieties. 2. Materials and methods 2.1. Phobic reactions in Virtual Reality Despite numerous studies, aimed at determination of various factors on immersion level, a problem of influence of display parameters on efficiency of therapeutic applications is not sufficiently explored. In many cases, the immersion level is determined indirectly by survey studies16. In case of applications used for phobia treatment, the higher immersion, the higher is subconscious conviction of patient that he is subjected to factors causing him phobic / repulsive reactions. The whole concept of exposure therapy is based on it11, so higher immersion obviously allows obtaining better treatment results. It translates into several stress-induced body reactions, such as increase of blood pressure, muscle vibration, accelerated heart beating, sweating etc17. In the initial phase of therapy, exposition level should be carefully selected, in order to not induce any violent reaction by the patient, then he can get gradually accustomed with the fear. Therefore, to study capabilities of a Virtual Reality display, patient reactions can be measured using a hardware such as a pulsometer. There is a need for an application, where both level of exposition (application content) and level of display-induced immersion (software and hardware parameters – image resolution, field of view – FOV, etc.) can be controlled, to study patient reactions. The more the patient is immersed into a virtual world, the stronger he will react to a stress-inducing situation, which will translate directly into measurement results18. 2.2. Case and problem definition – therapeutic application To study influence of display parameters on level of immersion, a therapeutic Virtual Reality application was prepared, intended for curing of acrophobia (also known as fear of heights). The application is an environment consisting of multi-floor buildings with moving platforms and lifts. It was created in the 3D Studio Max software. Prepared 3D data was imported to two different 3D engines – EON Studio and Unreal Engine. It these two engines, identical interaction functions were added – positional and rotational tracking of user and collision detection between character and environment, to ensure effects such as free fall or bouncing off walls and platforms. Similar visualization techniques have been used to make the application look almost the same. The EON Studio application was prepared for use with the professional HMD, while the Unreal Engine was adjusted to work with the low-cost VR devices, such as Oculus Rift or HTC Vive. The two separate engines were used for comparison of application building methodology, as well as for easiness of use (EON Studio has in-built tools for used professional VR hardware, but use of low-cost devices is limited, it is the opposite with the Unreal Engine). In both applications, long distance user movement was ensured by use of joystick, and the user is assumed to take a standing position, with slight walking allowed over short distance. Seated pose can be also taken by the user, limiting tracking to the head orientation, decreasing immersion. It is especially important in case of strong phobias, to allow patient taking more comfortable position.

Pawel Bun et al. / Procedia Computer Science 104 (2017) 445 – 451

a)

b)

Fig. 1. (a) 3D data in Unreal Engine ; (b) 3D data in EON Studio.

2.3. Hardware characteristics Initially, the application was designed to work with a professional HMD – nVisor MH60 by the nVis company, with large-area optical tracking system PPT X 4 (10 x 10 meters tracking space) and InertiaCube2 accelerometer for determining user head orientation (see Fig. 2a). Table 1 presents the initial setup parameters. Observing previous works and analyzing the literature, the authors have concluded that users of this type of HMDs complain about limited FOV and high weight of the HMD, causing discomfort at long-term use. Table 1. Initial setup parameters – nVisor MH60 HMD. Parameter name

Value

Resolution

1280x1024

FOV

60°

Mass

955 g

Communication

Integrated control box, tracking by network (separate computer)

Display distance to user pupil (mm)

23

Geometrical distortion

<15%

Adjustment possibilities

inter-pupillary distance, up-down, forward-backward, tilt,

IPD adjustment range (mm)

53 - 72

Display technology

LCOS

Tracking

3 DOF positional tracking – PPT X, 3 DOF rotational tracking – InertiaCube2

To check if it is possible to get improved results (better comfort with acceptable immersion level), it was decided to apply a low-cost HMD – Oculus Rift CV1 (see Fig. 2b). It is a new device and it has high FOV, integrated accelerometer, as well as very limited tracking space. Comparing to the initial setup, it is lighter, better for FOV, but worse in terms of resolution. Parameters of this device are presented in Table 2.

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Pawel Bun et al. / Procedia Computer Science 104 (2017) 445 – 451 Table 2. Parameters of Oculus Rift CV1. Parameter name

Value

Resolution

2160x1200

FOV

110

Mass

470g

Communication

USB for tracking and control, display by HDMI

Interaction

Windows compatible joystick remote control

Tracking

IR LED sensor – 3 DOF positional tracking, 1,5 x 1,5 m tracking space, built-in accelerometer for 3 DOF rotational tracking

Fig. 2. Two HMD devices used: (a) nVisor MH60; (b) Oculus Rift CV119.

3. Test procedure The users were presented with a task of moving themselves in a virtual space, along a path described by the authors, with unlimited time. The time was not measured and the users were informed about it. Competition between users was not an aim of the presented experiment and the users could spend as much time as needed, including pauses (if needed). One of kinematic tasks to perform was entering a moving platform, allowing both way vertical transportation between the ground level and the roof of the building. It is an especially stressful situation for persons experiencing fear of heights, moreover – it requires conscious decision to enter the platform and taking an appropriate kinematic action (i.e. walking onto the platform). The test group was presented with the task twice, initially using a professional HMD and using the low-cost hardware the second time. In the initial setup, most of transportation was performed using walking, in the low-cost setup the users were asked to transport themselves only using a joystick, however maintaining the standing posture if comfortable enough. The two approaches were done on two separate days, to prevent the “getting into habit” effect which could alter the pulsometer readings. During the study, the users reactions were observed and heart rate was measured. To define a reference point, before presented

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with the tasks, the users were placed in a neutral virtual environment and only after getting familiar with the hardware and software basics, their resting pulse was examined. The test group was divided into four groups, according to individual features: x x x x

Group I – with nor sight impairment neither fear of heights Group II – with both sight impairment and fear of heights Group III – with no sight impairment but with fear of heights Group IV – with sight impairment, without fear of heights

Total 20 persons participated in the study – 17 were male, 3 were female. Age of studied persons stayed within range of 23 to 32 years old. During the task (after the preparation phase and initial pulse measurement) each user was transported instantaneously to the roof of the building and had to perform the following actions: x x x x x x x

Enter one of the moving platforms Go one level down Leave the platform and enter a bridge between buildings Go to another platform Enter the platform Go down to the ground level Repeat the sequence in inverted order (get back to the roof using the same route)

The sight impaired persons were all myopic (i.e. shortsighted) and not using contact lenses, in favor of prescription glasses in daily life. That is why quality of received contents, supplied by the used VR systems does not necessarily have to be identical as in persons without sight impairment. It needs to be noted, that neither one of the used HMDs had construction features allowing comfortable use of prescription glasses, so the users had to remove their glasses for the simulation. Inside groups II and III (fear of heights), there were no patients with extreme case of acrophobia, not allowing normal everyday functioning. The persons determining themselves as fearing heights indicated, that the fear causes significant discomfort, manifesting itself by sweating, lower limb tremor, vertigo and accelerated heart rate. However, they never observed more serious consequences, such as losing consciousness or panic attack. These persons try to avoid experiences related to large heights (entering ladders, moving through small bridges, being at a balcony etc.) both in everyday life and at work. The groups I and IV contained persons without fear of heights, having no problems with activities related with exposure to heights, both in work and leisure. The pulse was measured using the Beurer PM200+ meter, noting one measurement per second. The resting pulse was measured in a sitting position, with no movement for 60 seconds before the measurement. Additionally, to confirm validity of measurement, the resting pulse was measured using the OMRON M2 HEM-7121-E device for measurement of blood pressure and pulse. Manual verification was additionally performed, checking pulse on the neck artery for 30 seconds. Differences in various measurements did not exceed 8% for most persons. However, for three persons the difference was higher than 20%, so results of these persons were not considered in the final comparison. Not all participating persons previously dealt with Virtual Reality systems. From authors’ experience it can be concluded, that it could influence the results, as using new hardware and technology may significantly affect work of a human body – usually it is insignificant or moderate excitement. This is especially visible while participating in group sessions, with one person immersed and other observing. To limit this influence, all studied persons were first familiarized with the equipment, but not with the application itself. The studies were performed individually, with only one other person present besides a given user.

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4. Discussion of results Persons belonging to the first studied group, as opposed to the others, have indicated that they regularly participate in sport activities or significant physical strain. That is why it is natural, that their pulse (also without physical load) will be lower than for persons, which are not physically fit. Persons without sight impairment but with fear of heights (group III) had problems with completing the tasks (see Table 3). All persons eventually finished the simulation, but traveling the defined distance took the persons from group III significantly more time. Using the full walking scenario with the nVisor HMD, their body movements were definitely less stable than in persons of other groups. They also reported typical reactions, such as vertigo and leg tremor, using both hardware setups. Table 3. Pulse values in beats per minute (bpm) divided by groups. Group

OCULUS CV1

nVisor MH 60

Min.

Max.

Mean

Range

Min.

Max.

Mean

Range

I

79,2

90,4

85,4

11,2

80,6

99,6

92

19

II

84,8

99,6

91,2

14,8

86,6

109,6

98,8

23

III

88,4

113,8

100

25,4

90

131

113,2

41

IV

82,4

95

86

15

84,2

104,8

96,2

20,6

Table 3 presents results of pulse measurements for different groups and simulations. Minimal pulse is the recorded resting pulse. Differences in pulse and its average value between simulation on two different HMDs are caused by different physical load in the two setups. In both simulations the users began while sitting, then they were standing, walking a bit as well as crouching. However, the nVisor HMD is considerably heavier, so it is natural for a healthy person to have increased pulse while wearing heavy things and doing physical exercises, like walking. Moreover, the nVisor-based simulation allowed larger tracking space, so the users could be independent on a joystick and rely only on their body movement as a way of transport, which made them move more intensively during performing the task. For groups I, II and IV, difference in mean value between Oculus Rift and nVisor HMDs was approx. 8 bpm, while the maximal recorded value was 10 bpm higher. For the group III, differences in measured values between simulations were significantly higher – 13,2 and 17,2 bpm for mean value and maximal value, respectively. The least value of recorded pulse for users in all groups was close in both simulations, although slightly higher for simulation with the nVisor. This could be caused by both the HMD weight and possibility of making natural movements (free walking). Only one person out of the group II (both myopic and acrophobic) could confirm feeling any kind of fear while using the Oculus, while for the nVisor it was two persons who indicated feeling a discomfort related to heights. It was confirmed by the recorded pulse – individual value of pulse for these persons was significantly higher than for other persons from this group, although still lower than for persons from group III. In case of the group III, maximal pulse was recorded during platform (elevator) ride – it is related to a fact, that the elevator cannot be controlled by the user and getting on and off the elevator requires a resolute movement, which may further increase the anxiety during the ride itself. 5. Conclusion The conducted studies have proven, that the low-cost, newly developed VR devices can be successfully used for building immersive Virtual Reality applications for exposure therapy of certain phobias. According to predictions, using large area tracking system allows better immersion, which translated into measured results. During the studies, a suggestion was made by the visually impaired participants, about a visual side of the simulation. Too small contrast between colors of platforms and building floors made it difficult to recognize, where platform’s edge is.

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Blurred image observed by myopic persons with no glasses and contact lenses heavily decreases the immersion level. Therefore, it needs to be concluded, that unless visually impaired persons wear contact lenses, Virtual Reality devices without certain design features (like interchangeable lens or adjustment mechanisms) will be of no big use for them. Nevertheless, as Virtual Reality Exposure Therapy was known before the low-cost VR devices emerged, now it can be made more widespread, thanks to availability of different cheap solutions. It would then allow patients to get wider access to this kind of therapy. The authors future work will focus on treating various phobias, using various low-cost Virtual Reality gear. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

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Pawel Bun is MSc. Eng., winner of competition BE THE BEST 2013, organized by Volkswagen Poznan. His research interests from the beginning of his work in the Department of Management and Production Engineering focused on the use of virtual reality systems, position tracking, visualization, interaction methods and its impact on the immersion. He is author and co-author of more than 20 publications. Contact him at [email protected].

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