Body Mental Representation in VR: Systematic Review

As a working definition, we consider the body mental representation (BMR) to be the mental reflection of its size, shape and position at any given time. BMR differs from the body scheme, since it includes a wider range of mental prerequisites for its occurrence. It is also a plastic and adaptively significant formation. This research focuses on a systematic review of a BMR distortions in VR. Research issue is, what psychologically significant factors are associated with distortion of BMR in VR? A total of 15 studies of scientific journals from the PubMed database 2011 to 2023 (Median = 2020, SD = 0,76) were analyzed and results were organized into three paradigms such as Rubber-Hand Illusion (RHI) study in VR (1), Full-Body Illusion (FBI) study in VR (2) or Visual-Motor Adaptation (VMA) study in VR ( 3).Exclusion criteria were: (1) non-fiction text, not peer-reviewed, or conference abstract; (2) a small or mathematically unjustified sample of respondents; (3) VR immersion without HMD; (4) the study was conducted on a clinical sample of respondents and represents a test of a therapeutic intervention; (5) the study described a mental representation of the avatar’s body in VR or an undifferentiated body representation; (6) body representation construct refers to self-perception of appearance, rather than size or position in space. In the studies reviewed respondents observed significant distortions in the body mental representation after VR immersion. However, their structure and hypothesized reasons often differ and are related to the experimental design used. In the RHI study, proprioceptive drift and ownership of a virtual limb are recorded in VR, which are caused by the respondent’s increased attention to the corresponding body part. FBI research shows the possibility of internalizing a visible avatar into the mental representation of respondents’ own body after VR immersion. Experiments with VMA demonstrate the possibility of using an updated body mental representation when performing VR activities. All researchers agree on the dominance of visual feedback for body representation in VR. The data indicate the adaptive significance of the identified distortions. These findings made it possible to formulate the 4 most important psychologically significant factors associated with the distortion of the mental representation of the body in VR: (1) Visual-Tactile congruence, (2) Visual-Proprioceptive congruence, (3) Visual-Motor congruence and (4) Functionality of the dominant image or sensory modality. A conclusion is drawn about the short-term and adaptive role of the observed BMR distortions in VR.

Ментальная репрезентация тела в виртуальной реальности: систематический обзор

Варламов А.В.
Рязанский государственный медицинский университет имени академика И.П. Павлов, Рязань, Российская Федерация. ORCID iD: 0000-0002-6144-6036

Аннотация: В качестве рабочего определения мы рассматриваем ментальную репрезентацию тела (МРТ) как мысленное отражение размера, формы и положения в тела в пространстве в любой момент времени. МРТ является пластичным и адаптивным образованием. Оно отличается от схемы тела, поскольку включает более широкий спектр психических предпосылок возникновения. Настоящее исследование посвящено систематическому обзору искажений ментальной репрезентации тела при погружении в виртуальную реальность. Исследовательский вопрос обзора состоит в выявлении психологически значимых факторов искажения ментальных репрезентации тела при погружении в виртуальную реальность. Из базы данных PubMed в соответствии с критериями включения и исключения отобраны и проанализированы 15 исследований с 2011 по 2023 год (медиана = 2020, стандартное отклонение = 0.76). Критериями исключения были: (1) научно-популярный текст, не прошедший рецензирование, или тезисы конференции; (2) небольшая или математически неоправданная выборка респондентов; (3) погружение в виртуальную реальность без шлема виртуальной реальности; (4) исследование проводилось на клинической выборке респондентов и представляет собой проверку терапевтического вмешательства; (5) исследование описывало мысленное представление тела аватара в виртуальной реальности или недифференцированное представление тела; (6) конструкция представления тела относится к самовосприятию внешнего вида, а не к размеру или положению в пространстве. Результаты организованы в три исследовательские парадигмы, такие как «Иллюзия резиновой руки» (RHI) в виртуальной реальности (1), иллюзии всего тела (FBI) в виртуальной реальности (2) или зрительно-моторные адаптации (VMA) в виртуальной реальности (3). В рассмотренных исследованиях респонденты обнаружены значительные искажения ментальных представлений тела после погружения в виртуальную реальность. Однако их структура и предполагаемые причины часто различаются и связаны с используемой схемой эксперимента. В исследовании RHI в VR фиксируются проприоцептивный дрейф и владение виртуальной конечностью, вызванные повышенным вниманием респондента к соответствующей части тела. Исследование FBI показывает возможность внедрения видимого аватара в мысленное представление собственного тела респондентов после погружения в виртуальную реальность. Эксперименты с VMA демонстрируют возможность использования обновленного мысленного представления тела при выполнении действий в виртуальной реальности. Все исследователи согласны с доминированием визуальной обратной связи при представлении тела в виртуальной реальности. Данные свидетельствуют об адаптивной значимости выявленных искажений. Эти данные позволили выявить 4 наиболее важных психологически значимых фактора, связанных с искажением мысленной репрезентации тела в виртуальной реальности: (1) Зрительно-тактильная конгруэнтность, (2) Зрительно-проприоцептивная конгруэнтность, (3) Зрительно-моторная конгруэнтность и (4) функциональность доминирующего образа или сенсорной модальности. Делается вывод о кратковременной и адаптивной роли наблюдаемых искажений BMR в VR.

Ключевые слова: ментальная репрезентация тела, VR, иллюзия резиновой руки, иллюзия всего тела, зрительно-моторная адаптация.

Introduction

Glossary

BMI – Body Mass Index
BMR – Body Mental Representation
FBA – Full Body Avatar
FBI – Full-Body Illusion
FPV – First Person View
HMD – Head-Mounted Display
MR – Mental Representation
RHI – Rubber-Hand Illusion
VMA – Visual-Motor Adaptation
VR – Virtual Reality (i.e. Immersive Virtual Reality)
VRET – Virtual Reality Emotional Therapy

1.1. Relevance

Modern VR technologies have reached a sufficient level of quality to quickly and reliably form the illusion of presence in a person’s mind (Weidner et. al., 2023). Headsets that are capable of smoothly generating images of three-dimensional virtual space are widely available to the mass consumer. This proliferation has increased the interest of researchers around the world in VR. This trend can also be traced in psychology. For example, a combined query for “virtual reality” & “psychology” in the PubMed database illustrates the sharp increase in research activity between 2017 and 2019 (Figure 1) (pubmed.ncbi.nlm.nih.gov).

Figure 1. Number of publications for the query “virtual reality” + “psychology” over the past 10 years in the PubMed.org database as of January 10, 2024.

The popularity of the VR topic is determined not only by the availability of modern equipment, but also by practical necessity. The areas of VR usage in professional activities are noticeably expanding (Taghian et. al., 2023), entertainment (Gurz et. al., 2023; Wang et. al., 2022), medicine (Yeung et. al., 2021; Ghaedna et. al., 2021), education (Plotzky et. al., 2021; Kye et. al., 2021). Currently, VR is the most immersive way to broadcast digital content (Radianti et. al., 2020). This promotes widespread inclusion of VR in education (Chen et. al., 2020; Uruthiralingam et. al., 2020) and psychotherapy (Emmelkamp et. al., 2021; Freeman et. al., 2017).

For immersive VR, first person view (FPV) is used. This makes it possible to simulate the presence of a real human body in digital space by maintaining the usual mechanisms of sensory perception. During VR immersion, a person experiences a body-related experience. Presumably, this experience is more effectively integrated into the mental space than conventional PC interaction. In other words, it is a person’s subjective idea of his own body (i.e., the body mental representation, BMR) that is actively involved in adaptation to VR conditions.

A large body of empirical research in VR confirms the presence of distortions in the BMR after immersion in VR (Serino et. al., 2016; Tosi et. al., 2020). Most of these studies were conducted on clinical samples, based on specific psychotherapeutic approaches. There are known results of the successful use of VR emotional therapy (VRET) to correct distorted body image in eating disorders (Magrini et. al., 2022; Calugi et. al., 2019). In a laboratory experiment, VR was able to form and consolidate adequate self-esteem of body size in patients with anorexia (Irvine et. al., 2020). Bodily disorders associated with chronic pain syndrome have been studied. Their correction is possible with the help of VRET (Senkowski et. al., 2016). Researchers’ positivism regarding the use of VR in the clinical psychology of body image disorders is well-founded and supported by empirical evidence. Various systematic reviews have suggested the possible development of the technology’s correction potential by increasing the number of sensory signals simulated in VR, including sensations from internal organs (Riva, et. al., 2019).

Despite the great interest of clinical researchers in bodily perception in VR, there has been no obvious progress in fundamentally studying the nature of these distortions. At the moment, there is no clear explanation for the cause of distortions in the mental representation of the human body when immersed in VR. Empirical data from non-clinical samples that could be used to develop a unified theory are limited in the literature (Pyasik et. al., 2022). This systematic review presents the analysis of current literature devoted to the BMR distortions after VR. The review brings together valid evidence from studies conducted on non-clinical samples of subjects. In this way, we expect to avoid possible artifacts associated with the initially impaired of the respondents’ BMR.

1.2. VR Experience
To justify the logic of the research, we use ideas about the subjective experience of a person immersed in VR. These ideas should be systematized and analyzed in terms of the role of the BMR in the acquisition of VR experiences. It should be emphasized that by VR we mean an illusion in a digital space, which is achieved through the direct transmission of virtual stimuli to the human senses (Lanier, 2017). In other words, the use of a special headset is a prerequisite for a VR experience. This experience has high interactivity, so further in this paragraph we will call the recipient of the VR environment a “player”.

Despite the strict technical requirements for matching the VR experience, the headsets themselves may come in different configurations. VR worlds can vary in the degree of elaboration and interactivity. The presence and quality of the projection of the player’s body into the VR environment – the avatar – should also be taken into account. The correlation of VR experience with the real experience of the player determines the widespread preservation of anthropomorphic features of the avatar. A detailed analysis of common VR environments based on three factors: (1) the required headset configuration, (2) the visual display of the avatar, and (3) the quality of feedback about the player’s virtual actions, is presented in Table 1.

As we can see (Table 1), the virtual reality experiences a player receives using any headset configuration is not a complete replacement for the real-life experience. VR experience integrates a person’s experiences and perceptions of both realities (VR and the physical world) that arise during immersion. There is necessity to analyze the experience of a virtual body, i.e. the player’s experience of correlating his/her body and the avatar’s body.

Figure 2. Methods for technical implementation of visual feedback about the avatar’s body in VR.

a) The respondent is using a VR immersion headset,
b) VR presents a full-body avatar (digital character),
c) VR presents a conditional avatar without lower limbs,
d) In VR, only projections of the headset tracked points are presented (helmet = head, controllers = hands),
e) There is no visual avatar in VR

Immersive VR integrates real body movements into interactions with digital space. Any activity in VR requires the player to perform a congruent movement in the real world. Although the VR headset does not directly affect tactile and proprioceptive sensitivity, it uses the player’s motor activity to control the avatar in VR. Thus, bodily experience is an essential part of VR immersion (Garcia, et. al., 2019). From a technical point of view, creating a complex tactile, proprioceptive and visual bodily experience requires the use of an avatar. Due to the existence of differences in the quality of the real human body motor tracking (see Table 1), it is possible to use special avatars for environments with different requirements for player activity. Based on a standard set of commercial headsets (HMD and controllers), let’s look at the most common avatars:

• Full-Body Avatar (Figure 2b) gives the player full visual information about the exact size and appearance. At the same time, due to the lack of leg tracking, artifacts of incongruent completion of their movements when moving often arise.
• Half-Body Avatar (Figure 2c) within its dimensions quite accurately corresponds to the position and pose of the player’s real body. This makes it suitable for use in dynamic VR environments, but unsuitable for activities that require high personalization (Cao et. al., 2020).
• The Head & Wrists Avatar (Figure 2d) provides minimal visual feedback about the avatar’s body, but its position closely matches the position of the player’s actual head and wrists. This is the type of avatar most often used for VR environments in the entertainment industry (beatsaber.com).
• No Avatar (Figure 2e). The complete absence of an avatar, with the player retaining the ability to move within the boundaries of the immersion safe area and look around. Most often used in VR environments with an allocentric perspective and minimal task dynamics. For example, in the VR game Moss VR (polyarcgames.com/games/moss), the third-person player moves virtual objects using controllers and helps the character escape from the maze. There is no visible player avatar in Moss VR. However, the player cannot abstract from his/her own BMR and perceives the game as an interaction with an interactive diorama.

The mentioned immersion methods provide sufficient insight into the mechanisms of avatar-mediated human interaction with VR. In fact, they differ only in the quality and quantity of feedback about the size, appearance and position in space of the avatar. All these methods take into account the player’s bodily experience to experience real-world situations in VR.

Figure 3. Possible bodily sensations of the respondent when immersed in VR.
a) The respondent is using a VR immersion headset,
b) The respondent feels the presence of his/her own physical body in VR (visualization),
c) The respondent feels embodied in the body of a digital avatar in VR (visualization),
d) The respondent does not feel the tactile connection of his own body with physical reality (visualization),
e) The respondent feels the integration of the digital avatar’s body image into his/her own physical body BMR (visualization).

The need for bodily experience in VR has not only a technical, but also a physiological basis. During immersion, the visual and auditory analyzers are busy processing VR information, while the remaining sensory systems continue to process physical reality stimuli. At the same time, the flows of sensory information are not always contradictory. On the contrary, VR environments are designed to evoke integration. Thus, when describing the “sense of presence” in a virtual environment, one of the classical criteria is considered to be the embodiment of one’s own body in VR (Kiryu et. al., 2007). In other words, immersion involves the approximation of two simultaneously perceived realities in the player’s mental space. BMR, as a key instrument for interaction with both realities, undergoes changes according to the following patterns: (1) Physical Presence, (2) Full-Body Illusion.

(1) Physical Presence (Figure 3b). Early ideas about the human experience of immersion in VR use the paradigm of direct bodily presence in digital space. Pioneers in the field of VR took into account the possibility of the player experiencing VR as himself/herself (Gonzales-Franco et. al., 2017). During immersion in VR, a person perceives the environment and interacts with it himself/herself. He/she seems to retain his/her own personality and bodily qualities. Accordingly, the sensations of the real body are transferred to VR, losing connection with physical reality (Figure 3d).

(2) Full-Body Illusion (Figure 3c). In modern research, the paradigm of the player’s embodiment in the visible body of an avatar during immersion in VR is popular. Many current methods for diagnosing embodiment take into account the subjective degree of the sense of ownership of the avatar’s virtual body (Roth et. al., 2020). FBI also implies a certain degree of integration in player’s representation of the avatar’s body into his/her own BMR after VR-immersion
(Figure 3d).

Both patterns cannot fully describe the subjective immersive experience in VR. Numerous studies provide empirical evidence of the existence of body image distortions in VR, which refute the assumption that a player’s own body image is transferred into VR (Serino et. al., 2016; Tosi et. al., 2020). At the same time, these distortions do not replace the player’s own BMR with ideas about the avatar’s body (Day, 2019).

Thus, the question on the origin of the observed distortions in the player’s bodily experience when immersed in VR is relevant. Using bodily experience for VR makes it highly immersive. However, neither the integration of a visible avatar into the player’s BMR, nor artificial illusions of perception in VR can unambiguously explain the nature of the observed distortions.

I believe that the concept of human body mental representation (BMR) in VR should include the dynamic reasons for their occurrence. Only a comprehensive analysis of the VR experience can explain the distortions it causes. In this review, I consider the reliable empirical evidence from the perspective of the context it was obtained. We believe that systematizing VR research based on the BMR construct allows us to take into account not only the very fact of distortions’ presence, but also the process of their formation. As a result of the review, I expect to gain insight into the role of these distortions in human adaptation to VR conditions.

Method

2.1. Selection of studies

Systematic search of peer-reviewed papers was provided. The search was carried out in the international scientific database PubMed.

Inclusion criteria

Articles with experimental design involving the use of HMD VR (i.e. IVR) technology to immerse subjects in virtual reality were included in the analysis. Other methods of generating a VR environment (using streaming video, CAVE systems, and other methods) were not considered within the framework of the review. The main research construct should have been body image, body schema, and body representation. Research on emotional or social assessment of appearance was not included in the scope of the review.

Exclusion criteria

Popular science texts and non-peer-reviewed works, including conference abstracts, were excluded from the final list of articles. I did not consider studies with small or mathematically unjustified samples and case studies. Studies that used an experimental design that did not justify the need to include HMD VR immersion of respondents were although excluded. I did not take into account studies conducted on clinical samples, as well as evaluations of the effectiveness of certain psychotherapeutic interventions in this review. Studies that examined the avatar’s body representation or undifferentiated body representation, rather than the body representation of the respondents themselves measured with valid methods were although excluded from the review.

Keywords

The search in the PubMed database was carried out using the specified set of keywords and phrases: VR Body ownership (63), VR Full-Body experience (16), VR perceived body (220), VR body mental representation (11), VR body scaling (156), VR dimension of body image (6), VR embodiment (228), VR body image (135), VR Out-of-Body Experience (4), VR sense of agency (44).

Searching results

The systematic search allowed us to reduce the initial selection of 406 results to 15 scientific publications. The PRISMA four-step diagram illustrates the screening process (Figure 4).

2.2. Paradigm

Publications selected in accordance with the inclusion criteria for this analysis were systematized from the main research paradigm point of view. In studies of the VR experience influence on a person’s BMR, three most common paradigms can be distinguished:

(1) RHI (Rubber-Hand Illusion) paradigm. It is based on experimental studies of the rubber hand illusion (Tsakiris & Haggard, 2005). An experimental design with synchronous visual-tactile stimulation of a separate area of the body is used to induce the illusion of possessing a virtual hand in participants. There is evidence of achieving a similar effect of possessing not only a virtual hand, but also a virtual belly (Normand et. al., 2011), legs (Tosi et. al., 2020) and other parts of the body.

(2). FBI (Full-Body Illusion) paradigm. It is an extension of the RHI paradigm and combines experimental research with synchronous visual-tactile stimulation to create the illusion of owning an entire virtual body. Various methods are used to achieve this effect – sequential formation of RHI for different limbs (Rubo et. al., 2019), tactile feedback-reinforcement when performing certain actions (Bhargava et. al., 2022), etc. Authors suggest a high practical psychotherapeutic and correctional significance of achieving the FBI illusion. But they are always limited by complicated laboratory conditions.

(3) VMA (Visual-Motor Adaptation) paradigm. There is usually no sensory stimulation to create the illusion of possessing a virtual body. The experimental impact is based on the manipulation of virtual objects using the movements of a real body. Visual feedback of movements within VR and proprioceptive sensations creates the illusion of owning a virtual body. ‘Flying’ hands and objects replacing them can serve as a virtual body. This paradigm is the most widespread among the mass VR user.

The systematization of the works included in this review according to these categories is presented in Table 2.

Consumer HMD models (Oculus HMD, HTC Vive HMD, etc.) are used in almost all publications included in the review. There were no publicly available consumer HMD models until 2016, so some researchers used laboratory headset prototypes, such as Normand’s empirical study (Normand et. al., 2011). Researchers use identical or very similar VR headsets to immerse respondents. However, there is no consensus regarding study on body image distortions. Moreover, there is a discrepancy (Table 2) in the combinations of the research paradigm (Paradigm), the complex of bodily activity of the respondent transferred to VR (Tracking) and avatar visualization (Avatar Type). For example, Hudson’s study uses the FBI and Full Body Avatar paradigm, but the respondent remains motionless (Hudson et. al., 2020). In the Porssut study, the RHI experiment is accompanied by respondents’ full body tracking and a dynamic task (Controllers + Trackers + Full Body Avatar) (Porssut et. al., 2022). This contradiction emphasizes the relevance of the problem. and requires clear systematization in this review.

Table 2. Systematization of the current scientific literature.

Results

Virtual Hand Illusion

Using the RHI paradigm (Tsakiris & Haggard, 2005) is a common way to study distortions of BMR in VR. The popularity of the RHI stems from the assumption that, based on the established proprioceptive drift, the immersion effect of the respondent in VR can be indirectly assessed (Limanowski, 2022).

The VR RHI experiment is fundamentally different from the classic RHI experiment. By using an HMD, there is no need to hide the respondent’s real hand from view when designing an experiment. The role of the material rubber hand during immersion is played by the controller projection. The respondent holds it in his/her own hand, hidden from the virtual view, or uses directly physical hands and sees their model through the Hand Tracking device. In dynamics, this experiment is more similar to a study of adaptation to a specific prosthetic limb or to training for exoskeleton control.

These differences have led some researchers to designate a separate paradigm for this experimental design Virtual Hand Illusion (VHI) (Sanchez-Vives et. al., 2010). I believe that this division is not obligatory due to the universality of the virtual limb embodiment process in the respondent’s BMR. Visual evidence of an illusion can be proprioceptive drift (Limanowski, 2022) in the perception of one’s own limb, or dynamic changes in errors in completing a task in VR using a virtual ‘rubber’ hand.

In Ambron’s study on 3 groups of respondents (average 40 young adults, 22F and 18M, mean age 24.03), a significant proprioceptive drift in the position of the respondents’ real hands towards the limbs visible in VR was achieved (Ambron et. al., 2020). Respondents played a matching card game of increasing difficulty. They were periodically asked to touch the index finger of one real hand to the index finger of the other real hand. However, the spatial position of the virtual hand (visual feedback) was different in all experiments. In Experiments 1 and 2, the active hand was displaced 7 or 14 centimetres higher or lower than the real one, and in Experiment 3 the passive (receiving) hand was displaced. For accurate tracking and data recording, HTC Hand Tracking was used, that is, the virtual hand, with the exception of its position in space, was an exact reproduction of the subjects’ real hand. Hand controllers were not used. Using Linear Models, a statistically expressed drift was calculated for each of the experiments based on motion errors (proportional distortion of 7.4%, 7%, and 7.8% towards the position of the virtual hand, respectively). According to the authors, the distortion in the perception of subjects’ own hand spatial position was influenced by distorted visual feedback based on an intentional tracking error.

In a number of works, the proprioceptive drift of the hand during immersion in VR is interpreted through a description of the peripersonal space involved in the immersion. In the space accessible through the limbs, any functional changes in the body are easily integrated into the respondent’s BMR.

Thus, in a study by Pyasik et. al. the boundaries of peripersonal space are determined through repeated assessment of the respondent’s reaction time in a situation of visual-tactile conflict (Pyasik et. al., 2021). In the VR experimental situation, respondents sat at a table and observed the avatar’s hands. On either side of the midline of the peripersonal space (table) there were two light bulbs that lit up periodically. The avatar’s left hand was extended toward one of two light bulbs in a position congruent or incongruent with the subjects’ real body. The right hand was placed on the knee under the table. An electrode was attached to the back of the subjects’ hand, which could give a light current discharge synchronously or asynchronously with the activation of the light bulb. The subjects had to respond to a tactile stimulus (electric shock) using a pedal under the table. Respondents have been told to ignore visual stimuli.

To evaluate the degree of embodiment of the virtual hand, reaction time was assessed. Comparative analysis of indicators for reaction time in different conditions (ANOVA) was used. In a female sample of respondents (average 26F, mean age 24 years, right-handed), a faster response to a tactile stimulus was found if the virtual hand was in identical to the respondent’s real hand position. Reaction times decreased when the tactile stimulus was reinforced by a flashing light in VR near the virtual hand. The authors conclude that the integration of peripersonal space conditions in VR is determined by two key parameters – the proximity of the perceived stimulus to the virtual body (1), as well as the congruence of the spatial position of the real and virtual hands (2).

A similar experimental design based on the concept of Spatial Numerical Associations of Response Code (SNARC Effect) was used in the study by Lohmann (Lohmann et. al., 2018). When the SNARC Effect occurs, a person learns to divide the peripersonal space into zones of achievement based on semantic (numerical) stimuli (Dehaene et. al., 2003). Typically, the left hand gets used to quickly reaching distant stimuli, and the right hand – closer ones. Lohmann et. al. use Hand Tracking to create an immersive VR experimental situation. In various combinations of the experimental condition, respondents, using their right or left hand, must indicate the numerical value of the virtual sphere distance, or refuse to complete it if the sphere is presented in extrapersonal space. In a series of 2 experiments (average 32 young adults, 16M and 16F, mean age 22.1), the successful occurrence of the SNARC effect in subjects was established. Moreover, by constructing a linear model of reaction time, more effective and accurate control over stimuli in the central zone of peripersonal space was revealed. The subjects demonstrated less confident reactions to stimuli either distant from the body or to stimuli very close to the body. The data provides evidence of the environmental friendliness of VR for SNARC research. In addition, as the authors note, in the experiment, at the level of tendency, a relationship was established between the accuracy of completing a task and the feeling of presence in the environment. This is consistent with the assumption that respondents integrate visual information about the virtual hands into their own BMR while completing the task.

Additional evidence can be found in Day’s dissertation (Day, 2019). The study was conducted on a sample of 28 respondents (average 28 students, 6M and 22F, mean age 18.68). Each respondent took part in a series of 130 trials (3 series of experimental treatments, 2 conditions). Subjects were asked to use virtual hands to indicate the distance required to reach a briefly presented object in VR. In the first experimental condition, respondents used regular HTC Vive hand controllers. In the second experimental condition, a modified version was used with the length of the virtual avatar’s arm being 28 centimetres longer than the length of the respondent’s real arm. The data obtained allow the authors to make a number of important assumptions about the integration of avatar hand sizes in a person’s image of his/her own body. Firstly, when analyzing the absolute error, the learning ability of the respondents was established. As the number of trials increased, the accuracy of the task increased. Secondly, at the post-test stage there is also an increase in movement accuracy in physical reality. The authors conclude that respondents recover a representation of their own hand size over time. The established patterns illustrate the gradual adaptation of respondents to the conditions of bodily reality changed with the help of VR. After the VR exposure ends, over time the distorted BMR returns to normal. We believe that these studies illustrate the instrumental function of a plastic BMR. Visual feedback about the size of one’s own hand and data on the success of activities in VR create the basis for the emergence of adaptive distortions in the one’s own BMR.

The technical features of modern VR headsets (Table 1) make it difficult to simulate tactile sensations congruent with VR conditions in respondents outside the laboratory. However, the question about their role in the resulting distortion of respondent’s BMR during immersion must also be answered.

In a study by McAnally et. al. provides comprehensive information on the importance of tactile feedback for manual accuracy (McAnally et. al., 2022). The experimental task was a reaction speed game in which the subjects had to place their finger on a red circle among a set of white circles. The experiment included 5 conditions – 1 on a touch screen monitor (1) and 4 in VR. At the same time, in VR tasks, different options for tactile feedback about the success of completing the task were used – (2) hybrid feedback (subjects touch the physical touch screen, which perfectly matches the position of the virtual touch screen) (3) passive tactile feedback (subjects touch a physical obstacle , but task completion is scored using VR collision), (4) active haptic feedback (successfully touching the virtual touchscreen is accompanied by controller vibration), and (5) no haptic feedback. Respondents (average 20 adults, 6M and 14F, mean age 31.5) demonstrated a gradual decrease in the speed of completing the task from condition 1 to condition 5 (conditions 2 and 3 were completed at an identical speed). The accuracy of task completion by respondents was assessed by the number of errors made. Condition 1 (touch screen in the physical world) produced the fewest errors, and no differences in the number of errors were found between Conditions 2–5. It can be concluded that the level of accuracy in completing the task is identical in VR conditions that differ in the quality of tactile feedback about the action of the hand. Apparently, when assessing the accuracy of the virtual hand’s actions, respondents were primarily guided by the visual channel of perception. Haptic feedback in VR is only related to the speed of completing tasks. It is likely that the quality of tactile feedback in VR only affects the speed of adaptation to VR conditions. In other words, tactile feedback is an important, but not necessary condition for the BMR distortion during immersion.

RHI studies in VR compare favorably with the physical version of the experiment, since they allow, along with visual-tactile stimulation, the use of a dynamic task with an embodied virtual hand. The studies reviewed address various practical and theoretical scientific problems and use experimental designs that differ in many factors. However, in all studies, the authors voice an identical observation about the importance of the visual channel of perception for the respondent’s adaptation to the experimental conditions. At the same time, the focus of the respondent’s attention, depending on the design of the experiment, is not always the virtual hand of the avatar. On the contrary, Lohmann et. al., Day and McAnally et. al. respondents’ attention is focused on completing the task. Distortions in the respondents’ own hands MR are observed in all studies.

To summarize, visual-tactile and visual-motor congruency are essential for performance in virtual reality. It is likely that during immersion, visual and proprioceptive feedback facilitate the integration of the virtual image of the hand and its motor activity into the respondent’s own BMR. However, it is visual feedback about the size and position of the hand, or about the effectiveness of the action, that should make a decisive contribution to the resulting distortion.

3.2. Body Ownership

The findings of the previous paragraph give reason to believe that the idea of “appropriating” a virtual hand during immersion in VR is not a correct interpretation of the respondent’s mental experience. The RHI paradigm requires increased attention to the study of the course of respondents’ cognitive processes. The illusion of owning a rubber or virtual hand is achieved, as we have established, due to two main mechanisms – visual-tactile congruence and visual-motor congruence. Consequently, the final MR of the hand should be a combination of memories of one’s own body and sensations distorted in accordance with the characteristics of the VR environment and virtual activity.

The hand as a body part is the main means of motor interaction with objects of the external world, therefore, when the respondent is immersed in new conditions (VR), the hand MR has a special adaptive significance. However, this thesis can be extended to the respondent’s body as a whole. In the theory of self-awareness, Body Ownership is a recognized condition for the adequacy of the experience of interaction with the outside world, since technically, all experience potentially available to a person in the process of life is bodily related (Gallagher, 2000). In this section, we review the current knowledge about the characteristics of bodily experience during immersion in VR. Research in this area is usually combined into the paradigm FBI (Full Body Illusion) or BOI (Body Ownership Illusion) (Pyasik et. al., 2022, Lopez et. al., 2008).

Modern VR headsets are available to track the player’s entire body and transfer his/her motor skills to VR (see Figure 2), but in most cases they are limited with hands and head tracking. At the same time, Full Body Avatar (FBA) are often used by developers without the ability to ensure their full spatial congruence with the position of the respondent’s real body. For example, in one of the most cited studies in the FBI paradigm, tracking is used only with a special device for respondents’ visual-tactile integration (Normand et. al., 2011). Respondents (average 22 thin men, mean age 26) were seated and immersed in a VR environment, so they could observe the body of a seated man with a large belly from a first-person view (FPV). On the table in front of the subjects there was a special stick device Its movements were transferred to VR. Respondents could independently move the device to touch their own physical abdomen. In VR, they observed a virtual stick touching an avatar’s virtual big belly. First, the authors found that the synchronous version of the experiment subjectively caused greater immersion in VR (visual-motor congruence and visual-tactile congruence). Secondly, after synchronous experimental exposure, a tendency was established to exaggerate the size of one’s own physical abdomen relative to its perception during asynchronous exposure (p = 0.052). In other words, in the experiment there is a distortion in the MR of the subjects’ abdomen size. Note that, according to the instructions, the respondents’ attention was focused on the visual display of the virtual character’s abdomen throughout the experiment.

A similar approach to FBI is presented in the Rubo et.al. study (Rubo et. al., 2019). The authors used a personalized FBA with biologically plausible technology to increase the displayed fat mass on the thighs. This FBA is calibrated according to the actual size of the respondent. The FBA is then proportionally enlarged based on the possible acquisition of fat deposits in the pelvic area. Respondents (average 40, 20M and 20F, BMI between 18.58 and 18.36) were divided into 2 groups. In group 1, avatar’s visual-tactile congruence with the respondent’s physical body was ensured (when the controllers are brought to the enlarged FBA’s pelvic area, the collision does not allow them to pass through the texture, so the controller’s touch to the FBA and the real body of the respondent were synchronous). In group 2, there was no visual-tactile congruence (when the controllers are brought to the avatar’s pelvis, their model passes through the texture until the physical controllers touch the respondent’s physical hips). After a short session in such conditions, respondents find themselves in a VR environment that reproduces the laboratory. Here respondents are asked to walk around obstacles (tables) so that when approaching their edges, the least possible safe distance remains. The results of the experiment clearly demonstrate significant differences between groups with intact and absent visual-tactile congruence. Respondents who saw the controllers pass through the texture of their FBA often passed the obstacles at the shortest distance, while respondents in the second group chose a greater distance to the objects. Probably, the respondents of the second group (with preservation of visual-tactile congruence) more comprehensively integrated visual information about the FBA’s body into their own BMR, since they observed a collision and perceived its texture as material. Consequently, respondents trusted the adequacy and functionality of its apparent dimensions.

Similar conclusions can be drawn from the Porssut et. al. study results. (Porssut et. al., 2022). In addition to the VR headset and hand controllers, the study used a set of additional Vive Trackers to accurately reproduce subjects’ upper limb motor skills in VR. While controlling the FBA in a seated position, respondents had to complete a series of tasks to combine two objects in VR. Depending on the stage of the experiment, the articular limits of the visible FBA changed, which caused a sensation of visual-proprioceptive incongruence. Respondents could be in one of 3 situations: the FBA’s arm movements fully match the respondent’s arm movements (1), the respondent’s arms are fully extended, and the FBA’s arms have not yet reached joint limits (2), the respondent’s arms have not yet reached joint limits, and the FBA’s arms are fully extended. extended (3). Feedback was based on self-report questions about the feeling of ownership of the FBA’s body after each attempt to complete the task. 25 young respondents (average 25, 16M and 9F, mean age 21.14) took part in the study. The authors make a number of unexpected conclusions. Firstly, the feeling of ownership of the FBA’s body is significantly higher in situation 3 than in situation 2. Secondly, the efficiency of completing the task in situation 3 is higher than in situation 2. The authors note that during the situation 3, respondents talked about a sense of control over two bodies simultaneously, as if the FBA were a functional exoskeleton or prosthesis. At the same time, when performing situation 2, respondents complained that the short arms of the FBA did not allow them to effectively perform the usual task. Apparently, it was easier for them to come to terms with unusually long, but functionally useful limbs than with short, but not helpful in performing a task. Thus, the role of the functionality of the FBA in the formation of a sense of ownership of the virtual body of the subjects is emphasized. In addition, it should be emphasized that these results clearly demonstrate the instrumental role of the visible FBA for the respondent. The more convenient the FBA is for achieving the goal of the experimental task, the more readily the respondent will integrate its features into his/her own BMR.

Previous studies use the FBI paradigm to manipulate Full-Body Avatars over time, combining visual feedback of the FBA’s visible body (1) and an experimental condition (task) to deliberately distort the BMR (2). This analysis requires establishing the separate contributions of these two VR immersion factors. The perception of visible FBA’s body follows the distortion in respondents’ own BMR. This fact has been revealed in more detail in studies of the perception of appearance and body image. A number of authors use the method of assessing avatars in VR that differ in various characteristics based on the thin-fat principle in order to modify respondents’ assessment of their own body.

Thus, in a study by Irvine et. al. on a preclinical sample, training was conducted to evaluate different avatars in VR to form an adequate self-esteem of the body among respondents (Irvine et. al., 2020). The training used reproduced a similar procedure for categorical assessment on a two-dimensional screen, in which respondents sequentially correlated briefly presented body silhouettes into the categories “thin” and “fat.” In VR, this training is reproduced from an allocentric perspective. Based on the immersion series results, respondents expanded the “thin” category and began to attribute more stimuli like “thin”. The respondents’ perceptual assessment of their own bodies has become more adequate. A similar principle was used in the study by Hudson et. al., however, personalized avatars were selected as stimulus material (Hudson et. a., 2020). Due to the complexity of modelling, only 10 female respondents took part in the study, but for each, a number of avatars were created based on body scans. At the same time, a number of models reproduced the respondent’s body with different body mass index (BMI) with anatomical accuracy. During a series of categorical comparisons, respondents began to more adequately correlate their own body with the avatar with the correct BMI. In other words, the results of the experiment achieved the same effect as Irvine et. al. However, the authors make an important conclusion about the difference in the perception of presented avatars in allocentric and egocentric perspectives – no correlations were found between these perception formats.

Clear evidence of egocentric avatar perception specificity in VR (or first-person view – FPV) can be found in Monthuy-Blanc (Monthuy-Blanc et. al., 2020). In an attempt to modify an operational tool for identifying body image distortions in individuals with eating disorders but in a preclinical sample in VR, the authors found fundamental differences in samples using allocentric and egocentric perspectives. The results of training on respondents in VR in an allocentric perspective reproduced the results of the eLoriCorps blank method with high accuracy. High correlations of test results for the criteria “Perceived Body Size”, “Body Distortion” and “Body Dissatisfaction” were established between the allocentric presentation of the test in VR and the blank method. At the same time, no significant correlations were found between these methods and the results of egocentric test presentation in VR. The authors note that this observation confirms the existence of a special mechanism for integrating the FBA’s body perceived from a first-person perspective into the respondent’s own BMR. The authors also connect this with the possible existence of intrapersonal changes in respondents during an egocentric VR immersion.

I believe that conclusions about the distortion of perception of one’s own body size based on judgments of the appearance of a VR avatar visible may be hasty. At the same time, the lack of correlation between the results of egocentric and allocentric immersions in the Monthuy-Blanc study gives reason to believe that there is a special mechanism for integrating, among other things, the dimensions of the virtual body into the respondents’ ideas about their own body.

The studies reviewed in this block invariably come to the conclusion that observing and performing actions on behalf of the Full-Body Avatar is accompanied by specific distortions in the one’s own BMR. The results of studies of body perception in VR, performed in the FBI paradigm, demonstrate the high role of visual-proprioceptive and visual-tactile congruence. From the point of view of the concept of body mental representation, it can be assumed that during immersion, respondents’ BMR undergoes temporary changes caused by the VR adaptation process.

3.3. Visual-Motor Adaptation in VR

The Visual-Motor Adaptation (VMA) paradigm involves designing an experiment in which respondents, while immersed in VR, control an avatar that differs from their own body in a number of ways (Limanowski, 2022). Assessing this condition from a technical point of view, it should be noted that the majority of modern VR environments are based on this paradigm (see Table 1). Thus, the use of “flying hands” as an avatar, which are projections of hand controllers, also falls under the definition of controlling a modified body. From a functional point of view, visual-motor adaptation is the process of mental adaptation to the implementation of activities based on body movements in unusual conditions. In other words, this paradigm includes studies in which concentration on the avatar’s body (or part of its body) is not the main activity of the respondent in the experimental task.

In studies by Bhargava et. al. an experimental design developed in the VMA paradigm was used (Bhargava et. al., 2022; Bhargava et. al., 2023). At the beginning of the experiment, respondents were divided into 2 groups. Respondents of the first group completed tasks, having previously been embodied in an avatar corresponding to their size (self-avatar). Respondents of the second group completed tasks without a visual avatar. As part of the experimental task, respondents were required, based on the perceived size of their own body and a visual object in their hands (a cylinder held by hand controllers), to make a judgment about the possibility or impossibility of passing through a slightly open doorway. After making a judgment, they could test its validity in practice. The width of the doorway in VR corresponded to the width of the physical door layout, so that respondents felt haptic feedback when they failed to overcome an obstacle. The width of the doorway, as well as the length of the cylinder, varied from 0.8 to 1.2 times the width of the respondent’s (and his/her avatar’s) shoulders, respectively.

In the first study, the authors make several important conclusions. An analysis of a positive decision about the ability to pass through a displayed doorway in various situations shows that judgments are made primarily based on the apparent length of the object in the hands of respondents (Bhargava et. al., 2022). The relationship between the apparent width of a doorway and judgment was not obvious. Moreover, the researchers note that in the group of respondents whose immersion was based on a self-avatar, the final decision was more accurate than in the group of respondents whose visual judgment could only be determined by the visible object in their hands.

A second study, based on a similar experimental design, extends these findings (Bhargava et. al., 2023). Unlike the first study, here respondents had to walk sideways through a virtual doorway. In this perspective, subjects also tended to rely on visual feedback when making decisions, but there was a significant increase in proprioceptive experiences. The subjects here more often made erroneous judgments about the possibility of squeezing through the opening and tried to test them by “shrinking” their body, as if they were performing a task in the physical world. This strategy is not possible in VR due to the limitations of real-time body size tracking. Therefore, it was unsuccessful under experimental conditions. The continuity of results is obvious:

• In the first experiment, it was proven that subjects, when adapting to VR conditions, try to rely primarily on visual feedback about virtual objects that are significant for completing the task (the visible body of the avatar and the object in virtual hands).
• The second experiment showed that with a deficiency of this feedback in conditions of the need to complete a task, subjects can use proprioceptive sensations.

In his review of the current literature on neurocognitive studies of body representation, Limanowski calls this phenomenon precision flexible control, since it is based on the modification of the significance of feedback by the human brain (Limanowski, 2022). Thus, the assumption about the flexibility of the human body representation is confirmed, as well as the possibility of using different types of feedback to adapt the body representation to changing environmental conditions.

Of note is the study by Karnath et. al., from the results of which it indirectly follows that in adapting the body representation, visual, tactile and proprioceptive feedback channels are of greatest importance (Karnath et. al, 2019). The authors test the assumption of the contribution of vestibular sensitivity to BMR. For this purpose, a VR environment was created in which respondents, by simply operating a controller, had to adjust the position of two objects in virtual space so that one of them could be reached with their middle finger, and the second with their heel. The respondents performed the task in a lying position and were divided into 2 groups. Before completing the task, respondents in the first group were induced to experience disturbances in vestibular sensitivity and dizziness by irrigating the eardrum with cold water. The second group of respondents was the control group. The authors did not find significant differences in the distances chosen by respondents of both groups as corresponding to their own body sizes. Moreover, respondents from both groups chose a distance that was adequate to their own size while performing the task. The direct conclusion about the absence of influence of vestibular sensitivity on the perception of one’s own size when immersed in VR indirectly confirms the role of other sensitivity channels, as well as the conclusions of other research teams.

Finally, let’s look at the study by Tosi et. al., the results of which clearly demonstrate the emergence of a complex distortion of respondents’ own BMR during immersion in VR (Tosi et. al., 2020). Before the immersion, the authors conducted a visual-tactile congruent stimulation session to create a Body Ownership Illusion (BOI). The first group of respondents observed a body with anatomically correct legs in VR, and the second group saw a body with elongated legs. Then the respondents were immersed in a VR environment, where they saw a deserted, endless space. In the experiment, they briefly saw a cone at a certain distance from the starting point. By pressing a button, they began moving at a constant speed in the direction where the cone was located. By pressing the button again, they signalled that they had travelled a distance that, in their impression, corresponded to the distance to the cone visible during exposure. Respondents from the experimental group (who were previously embodied in a body with long legs) pressed the button faster than the respondents of the second group. In other words, they believed they walked a longer distance faster. Questionnaire data showed that respondents from the control group were more willing to perceive an anatomically correct body as an avatar and embodied themselves in it. The data obtained probably most clearly demonstrates the influence of a distorted BMR on task performance in VR. Based only on short-term exposure to the principle of visual-tactile integration, they transferred the features of the associated body to the their own BMR, which directly influenced the performance of the experimental task. It should be noted that this work is considered in the review in the block of VMA, although it may also refer to the block of FBI. The final distribution is based on two factors. Firstly, implementation in this study is not the main, but only the preparatory activity of the respondents for the main stage. Secondly, there is no visible avatar during the experiment. A similar comment should be made about the distribution of studies by Bhargava et. al. (Bhargava et. al., 2022; Bhargava et. al., 2023). Regardless of the fact that half of the respondents were previously embodied in a FBA, when performing the main experimental task, its visible part was an additional, but not the main source of information for orientation in space and decision-making.

The studies discussed in this block illustrate the complex nature of BMR distortions during immersion in VR. On the one hand, there is evidence of the visual feedback dominance when distorting BMR (Tosi et. al., 2020; Bhargava et. al., 2022; Varlamov, 2022). On the other hand, it is clear that tactile and proprioceptive sensitivity also play a role in adapting to new VR environments. All types of sensitivity are used when analyzing the results of person’s activities. I believe that it is the functional significance of a certain feedback modality that determines its contribution to the overall person’s BMR distortion when immersed in VR.

Discussion

Numerous experiments with a rubber hand confirm that a person involved in interaction with an external object tends to integrate it into his/her own mental experience. Thanks to prolonged visual-tactile synchronous stimulation of the respondent’s rubber and real hand, it is possible to achieve the illusion of perceiving a foreign object as part of one’s own body (Tsakiris, Haggard, 2005). A similar phenomenon has been described in engineering psychology. For example, these include the operational image concept by D.A. Oshanin (Oshanin, 1973). Long-term use of an external object for instrumental purposes allows you to integrate it into the mental space of your own body (a stick as an extension of your hand). In other words, there is evidence that one phenomenon can be based on 2 mechanisms – synchronization of sensory stimuli of different nature (RHI) or motor instrumental activity with an object (operational image, VMA).

Studies using the FBI paradigm also support this observation. The authors obtain similar conclusions about the high importance of visual feedback in distorting respondents’ BMR. However, visual feedback itself does not describe the entire mechanism of this distortion, since it is part of the complex work of feedback of various modalities. Visual-tactile synchronous influence allows you to create the illusion of embodiment in the avatar with proportions different from the respondent’s real body (Normand et. al., 2011). But a categorical assessment of the avatar (Irvine et. al., 2020), as well as performing object-related activities on behalf of the avatar in VR (Porssut et. al., 2022) also lead to a similar effect. Thus, the visible body of the avatar, as in the case of RHI in VR, is only one of the factors influencing the distortion of respondents’ BMR.

These mechanisms can be combined in terms of body mental representation (BMR, representative-cognitive structures) (Chuprikova, 1997). Within the structural-dynamic approach, mental representation is the result and the process of a person’s habitual idea of his/her own body integration. All of the BMR changes achieve required to adapt to the current situation. The most complete picture is provided by data of experiments performed in the VMA paradigm, since they take into account feedback from various sensory modalities. Evidence from current research suggests the contribution of haptic feedback (Tosi et. al., 2020) and proprioceptive feedback (Bhargava et. al., 2022) to distorting respondents’ BMR. Moreover, it is the experimental design chosen by the authors that appears to be a direct predictor of specific, adaptive distortions in BMR. Thus, the identified BMR distortions in VR are most likely the result of adaptive mental activity.

Conclusions

To summarize, we list the factors identified in this review that are associated with BMR distortions in VR:

1. Visual-Tactile congruence. When using the synchronous visual-tactile stimuli to the respondent’s body and to the virtual avatar, the feeling of owning a virtual body is usually achieved.
2. Visual-Proprioceptive congruence. Researchers’ data indicate that the correspondence between the spatial position of the visible part of the avatar and the respondent’s physical body has a positive effect on their correlation in MR. This in turn leads to their temporary adaptively significant integration.
3. Visual-Motor congruence. The adequacy of feedback about the action being performed in VR, apparently, also contributes to the emergence of adaptive distortions in respondent’s BMR.
4. Functionality. The object’s functional significance for performing an intra-environmental task in VR can lead to its instrumental integration into respondent’s BMR. This principle also applies to the visible parts of the avatar’s body in VR. In addition, when choosing a dominant modality of sensory feedback, the brain is based on its actual adaptive significance. As a result, various distortions in the BMR have been observed in different studies.

There is a shortage of studies conducted on non-clinical samples in the scientific literature. Striving for a practical result, researchers ignore the current need to form a unified theoretical basis for the influence of immersion in VR on a person’s body perception.

This systematic review shows that the BMR have adaptive significance. Depending on the experimental design, it is possible to establish the influence of various sensory modalities (visual, tactile, proprioceptive) on the feedback distortions occurrence. Obviously, for the necessary distortion to occur, an increased concentration of a person’s attention on one or another aspect of the activity being performed is required, which in the case of VR is always based on the correlation of the movements of the real body and the avatar movement (if available). According to the Bayesian inference model, at any given moment in time the BMR is influenced by the sensation from the sensory modality with the greatest “weight,” i.e. most significant for the continuation of activities (Limanowski, 2022). This model explains the plasticity and adaptability of the BMR to intensely changing environmental conditions and allows us to provide a unified theoretical justification for various distortions that are recorded in studies.

The results of this review will be useful in preparing and interpreting the results of further research of BMR distortions in VR.

Competing interests: The author declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

1. Ambron, E., Miller, A., Connor, S., & Branch Coslett, H. (2020). Virtual image of a hand displaced in space influences action performance of the real hand. Scientific Reports, 10(1), https://doi.org/10.1038/s41598-020-66348-4
2. Beat Saber – VR rhythm game. (n.d.). Retrieved February 3, 2024, from https://beatsaber.com/
3. Bhargava, A., Venkatakrishnan, R., Venkatakrishnan, R., Lucaites, K., Solini, H., Robb, A. C., Pagano, C. C., & Babu, S. V. (2023). Can I Squeeze Through? Effects of Self-Avatars and Calibration in a Person-Plus-Virtual-Object System on Perceived Lateral Passability in VR. IEEE Transactions on Visualization and Computer Graphics, 29(5), 2348–2357. https://doi.org/10.1109/TVCG.2023.3247067
4. Bhargava, A., Venkatakrishnan, R., Venkatakrishnan, R., Solini, H., Lucaites, K., Robb, A. C., Pagano, C. C., & Babu, S. V. (2022). Did I Hit the Door? Effects of Self-Avatars and Calibration in a Person-Plus-Virtual-Object System on Perceived Frontal Passability in VR. IEEE Transactions on Visualization and Computer Graphics, 28(12), 4198–4210. https://doi.org/10.1109/TVCG.2021.3083423
5. Calugi, S., & Dalle Grave, R. (2019). Body image concern and treatment outcomes in adolescents with anorexia nervosa. International Journal of Eating Disorders, 52(5), 582–585. https://doi.org/10.1002/eat.23031
6. Cao, Y., Qian, X., Wang, T., Lee, R., Huo, K., & Ramani, K. (2020). An Exploratory Study of Augmented Reality Presence for Tutoring Machine Tasks. Proceedings of the 2020 CHI Conference on Human Factors in Computing Systems, 1–13. https://doi.org/10.1145/3313831.3376688
7. Chen, F.-Q., Leng, Y.-F., Ge, J.-F., Wang, D.-W., Li, C., Chen, B., & Sun, Z.-L. (2020). Effectiveness of Virtual Reality in Nursing Education: Meta-Analysis. Journal of Medical Internet Research, 22(9), https://doi.org/10.2196/18290
8. Chuprikova, N. I. (1997). Psychology of mental development: the principle of differentiation. JSC “Stoletie”; Books (published from 1831 to the present). [Chuprikova, N. I. (1997). Psikhologiya umstvennogo razvitiya: printsip differentsiatsii. AO “Stoletiye”; Knigi (izdannyye s 1831 g. po nastoyashcheye vremya)].
9. Day, B., Ebrahimi, E., Hartman, L. S., Pagano, C. C., Robb, A. C., & Babu, S. V. (2019). Examining the effects of altered avatars on perception-action in virtual reality. Journal of Experimental Psychology: Applied, 25(1), 1–24. https://doi.org/10.1037/xap0000192
10. Dehaene, S., Piazza, M., Pinel, P., & Cohen, L. (2003). Three Parietal Circuits for Number Processing. Cognitive Neuropsychology, 20(3–6), 487–506. https://doi.org/10.1080/02643290244000239
11. Emmelkamp, P. M. G., & Meyerbröker, K. (2021). Virtual Reality Therapy in Mental Health. Annual Review of Clinical Psychology, 17, 495–519. https://doi.org/10.1146/annurev-clinpsy-081219-115923
12. Freedom Locomotion VR by HugeRobot. (n.d.). Retrieved February 3, 2024, from https://hugerobot.itch.io/freedom-locomotion-vr
13. Freeman, D., Reeve, S., Robinson, A., Ehlers, A., Clark, D., Spanlang, B., & Slater, M. (2017). Virtual reality in the assessment, understanding, and treatment of mental health disorders. Psychological Medicine, 47(14), 2393–2400. https://doi.org/10.1017/S003329171700040X
14. Gallagher, I. (2000). Philosophical conceptions of the self: implications for cognitive science. Trends in Cognitive Sciences, 4(1), 14–21. https://doi.org/10.1016/s1364-6613(99)01417-5
15. Ghaednia, H., Fourman, M. S., Lans, A., Detels, K., Dijkstra, H., Lloyd, S., Sweeney, A., Oosterhoff, J. H. F., & Schwab, J. H. (2021). Augmented and virtual reality in spine surgery, current applications and future potentials. The Spine Journal, 21(10), 1617–1625. https://doi.org/10.1016/j.spinee.2021.03.018
16. Gonzalez-Franco, M., & Lanier, J. (2017). Model of Illusions and Virtual Reality. Frontiers in Psychology, 8, https://doi.org/10.3389/fpsyg.2017.01125
17. Gurz, D., Coimbatore Dada, K., Naga Nyshita, V., Aderibigbe, F. D., Singh, M., Yadav, K. P., Shah, S. K., Pumbhadia, B., Abbas, K., Khan, W., & Kumaran, V. (2023). The Impact of Virtual Reality (VR) Gaming and Casual/Social Gaming on the Quality of Life, Depression, and Dialysis Tolerance in Patients with Chronic Kidney Disease: A Narrative Review. Cureus, 15(9), https://doi.org/10.7759/cureus.44904
18. Home | Museum of Other Realities. (n.d.). Retrieved February 3, 2024, from https://www.museumor.com/
19. Home: Welcome to the website of OhShape, the rhythm VR game. (n.d.). OhShape. Retrieved February 3, 2024, from https://172.31.21.222/
20. https://search.rsl.ru/ru/record/01001781283
21. Hudson, G. M., Lu, Y., Zhang, X., Hahn, J., Zabal, J. E., Latif, F., & Philbeck, J. (2020). The Development of a BMI-Guided Shape Morphing Technique and the Effects of an Individualized Figure Rating Scale on Self-Perception of Body Size. European Journal of Investigation in Health, Psychology and Education, 10(2), 579–594. https://doi.org/10.3390/ejihpe10020043
22. Irvine, K. R., Irvine, A. R., Maalin, N., McCarty, K., Cornelissen, K. K., Tovée, M. J., & Cornelissen, P. L. (2020). Using immersive virtual reality to modify body image. Body Image, 33, 232–243. https://doi.org/10.1016/j.bodyim.2020.03.007
23. Karnath, H.-O., Kriechel, I., Tesch, J., Mohler, B. J., & Mölbert, S. C. (2019). Caloric vestibular stimulation has no effect on perceived body size. Scientific Reports, 9(1), https://doi.org/10.1038/s41598-019-47897-9
24. Kiryu, T., Iijima, A., & Bando, T. (2007). Relationships between sensory stimuli and autonomic nervous regulation during real and virtual exercises. Journal of NeuroEngineering and Rehabilitation, 4(1), https://doi.org/10.1186/1743-0003-4-38
25. Kye, B., Han, N., Kim, E., Park, Y., & Jo, S. (2021). Educational applications of metaverse: possibilities and limitations. Journal of Educational Evaluation for Health Professions, https://doi.org/10.3352/jeehp.2021.18.32
26. Lanier, J. (2017). Dawn of the New Everything: Encounters with Reality and Virtual Reality. Henry Holt and Company.
27. Limanowski, J. (2022). Precision control for a flexible body representation. Neuroscience & Biobehavioral Reviews, 134, 104401. https://doi.org/10.1016/j.neubiorev.2021.10.023
28. Lohmann, J., Schroeder, P. A., Nuerk, H.-C., Plewnia, C., & Butz, M. V. (2018). How Deep Is Your SNARC? Interactions Between Numerical Magnitude, Response Hands, and Reachability in Peripersonal Space. Frontiers in Psychology, 9. https://www.frontiersin.org/articles/10.3389/fpsyg.2018.00622
29. Lopez, C., Halje, P., & Blanke, O. (2008). Body ownership and embodiment: Vestibular and multisensory mechanisms. Neurophysiologie Clinique/Clinical Neurophysiology, 38(3), 149–161. https://doi.org/10.1016/j.neucli.2007.12.006
30. Magrini, M., Curzio, O., Tampucci, M., Donzelli, G., Cori, L., Imiotti, M. C., Maestro, S., & Moroni, D. (2022). Anorexia Nervosa, Body Image Perception and Virtual Reality Therapeutic Applications: State of the Art and Operational Proposal. International Journal of Environmental Research and Public Health, 19(5), https://doi.org/10.3390/ijerph19052533
31. McAnally, K., & Wallis, G. (2022). Visual–haptic integration, action and embodiment in virtual reality. Psychological Research, 86(6), 1847–1857. https://doi.org/10.1007/s00426-021-01613-3
32. Monthuy-Blanc, J., Bouchard, S., Ouellet, M., Corno, G., Iceta, S., & Rousseau, M. (2020). “eLoriCorps Immersive Body Rating Scale”: Exploring the Assessment of Body Image Disturbances from Allocentric and Egocentric Perspectives. Journal of Clinical Medicine, 9(9), https://doi.org/10.3390/jcm9092926
33. Moss | Polyarc Games. (n.d.). Retrieved February 3, 2024, from https://www.polyarcgames.com/games/moss
34. Normand, J.-M., Giannopoulos, E., Spanlang, B., & Slater, M. (2011). Multisensory Stimulation Can Induce an Illusion of Larger Belly Size in Immersive Virtual Reality. PLOS ONE, 6(1), https://doi.org/10.1371/journal.pone.0016128
35. Oshanin, D. A. (1973). Subject action and operative image: Abstract of thesis. for the degree of Doctor of Psychology. (21960) [b. And.]. Abstracts of dissertations. [Oshanin, D. A. (1973). Predmetnoye deystviye i operativnyy obraz: Avtoreferat dis. na soiskaniye uchenoy stepeni doktora psikhologicheskikh nauk. (21960) [b. i.]. Avtoreferaty dissertatsiy]. https://search.rsl.ru/ru/record/01007177968
36. Plotzky, C., Lindwedel, U., Sorber, M., Loessl, B., König, P., Kunze, C., Kugler, C., & Meng, M. (2021). Virtual reality simulations in nurse education: A systematic mapping review. Nurse Education Today, 101, https://doi.org/10.1016/j.nedt.2021.104868
37. Porras Garcia, B., Ferrer Garcia, M., Olszewska, A., Yilmaz, L., González Ibañez, C., Gracia Blanes, M., Gültekin, G., Serrano Troncoso, E., & Gutiérrez Maldonado, J. (2019). Is This My Own Body? Changing the Perceptual and Affective Body Image Experience among College Students Using a New Virtual Reality Embodiment-Based Technique. Journal of Clinical Medicine, 8(7), https://doi.org/10.3390/jcm8070925
38. Porssut, T., Blanke, O., Herbelin, B., & Boulic, R. (2022). Reaching articular limits can negatively impact embodiment in virtual reality. PLOS ONE, 17(3), https://doi.org/10.1371/journal.pone.0255554
39. Pyasik, M., & Pia, L. (2021). Owning a virtual body entail owning the value of its actions in a detection-of-deception procedure. Cognition, 212, https://doi.org/10.1016/j.cognition.2021.104693
40. Pyasik, M., Ciorli, T., & Pia, L. (2022). Full body illusion and cognition: A systematic review of the literature. Neuroscience & Biobehavioral Reviews, 143, https://doi.org/10.1016/j.neubiorev.2022.104926
41. Radianti, J., Majchrzak, T. A., Fromm, J., & Wohlgenannt, I. (2020). A systematic review of immersive virtual reality applications for higher education: Design elements, lessons learned, and research agenda. Computers & Education, 147, 103778. https://doi.org/10.1016/j.compedu.2019.103778
42. Riva, G., Wiederhold, B. K., & Mantovani, F. (2019). Neuroscience of Virtual Reality: From Virtual Exposure to Embodied Medicine. Cyberpsychology, Behavior, and Social Networking, 22(1), 82–96. https://doi.org/10.1089/cyber.2017.29099.gri
43. Roth, D., & Latoschik, M. E. (2020). Construction of the Virtual Embodiment Questionnaire (VEQ). IEEE Transactions on Visualization and Computer Graphics, 26(12), 3546–3556. https://doi.org/10.1109/TVCG.2020.3023603
44. Rubo, M., & Gamer, M. (2019). Visuo-tactile congruency influences the body schema during full body ownership illusion. Consciousness and Cognition, 73, https://doi.org/10.1016/j.concog.2019.05.006
45. Sanchez-Vives, M. V., Spanlang, B., Frisoli, A., Bergamasco, M., & Slater, M. (2010). Virtual Hand Illusion Induced by Visuomotor Correlations. PLOS ONE, 5(4), https://doi.org/10.1371/journal.pone.0010381
46. Senkowski, D., & Heinz, A. (2016). Chronic pain and distorted body image: Implications for multisensory feedback interventions. Neuroscience & Biobehavioral Reviews, 69, 252–259. https://doi.org/10.1016/j.neubiorev.2016.08.009
47. Serino, S., Pedroli, E., Keizer, A., Triberti, S., Dakanalis, A., Pallavicini, F., Chirico, A., & Riva, G. (2016). Virtual Reality Body Swapping: A Tool for Modifying the Allocentric Memory of the Body. Cyberpsychology, Behavior, and Social Networking, 19(2), 127–133. https://doi.org/10.1089/cyber.2015.0229
48. Space Maze | Redox Entertainment Inc. (n.d.). Retrieved February 3, 2024, from https://redox.ca/portfolios/space-maze/
49. Stress Level Zero. (n.d.). Retrieved February 3, 2024, from https://www.stresslevelzero.com/
50. Taghian, A., Abo-Zahhad, M., Sayed, M. S., & Abd El-Malek, A. H. (2023). Virtual and augmented reality in biomedical engineering. BioMedical Engineering OnLine, 22(1), https://doi.org/10.1186/s12938-023-01138-3
51. Team, E. (2022, December 12). Exploring Facebook’s Metaverse: The Web3 Cyberspace. Metaverse VR Now. https://metaversevrnow.com/vr/facebooks-metaverse/
52. Tosi, G., Parmar, J., Dhillon, I., Maravita, A., & Iaria, G. (2020). Body illusion and affordances: the influence of body representation on a walking imagery task in virtual reality. Experimental Brain Research, 238(10), 2125–2136. https://doi.org/10.1007/s00221-020-05874-z
53. Tsakiris, M., & Haggard, P. (2005). The Rubber Hand Illusion Revisited: Visuotactile Integration and Self-Attribution. Journal of Experimental Psychology: Human Perception and Performance, 31(1), 80–91. https://doi.org/10.1037/0096-1523.31.1.80
54. Uruthiralingam, U., & Rea, P. M. (2020). Augmented and Virtual Reality in Anatomical Education – A Systematic Review. Advances in Experimental Medicine and Biology, 1235, 89–101. https://doi.org/10.1007/978-3-030-37639-0_5
55. Vankrupt Games. (n.d.). Retrieved February 6, 2024, from https://www.vankrupt.com/#pavlov-vr
56. Varlamov A.V. (2022). Body Sizes Mental Representations Distortions during VR Immersions. Natural Systems of Mind, 2(3). https://doi.org/10.38098/nsom_2022_02_03_06
57. Video in virtual reality format – YouTube. (n.d.). [Video v formate virtual’noy real’nosti – YouTube. (n.d.).]. Retrieved February 3, 2024, from https://www.youtube.com/@360/featured
58. (n.d.). Retrieved February 3, 2024, from https://hello.vrchat.com/
59. Wang, L., Chen, J.-L., Wong, A. M. K., Liang, K.-C., & Tseng, K. C. (2022). Game-Based Virtual Reality System for Upper Limb Rehabilitation After Stroke in a Clinical Environment: Systematic Review and Meta-Analysis. Games for Health Journal, 11(5), 277–297. https://doi.org/10.1089/g4h.2022.0086
60. Weidner, F., Boettcher, G., Arboleda, S. A., Diao, C., Sinani, L., Kunert, C., Gerhardt, C., Broll, W., & Raake, A. (2023). A Systematic Review on the Visualization of Avatars and Agents in AR & VR displayed using Head-Mounted Displays. IEEE Transactions on Visualization and Computer Graphics, 29(5), 2596–2606. https://doi.org/10.1109/TVCG.2023.3247072
61. Yeung, A. W. K., Tosevska, A., Klager, E., Eibensteiner, F., Laxar, D., Stoyanov, J., Glisic, M., Zeiner, S., Kulnik, S. T., Crutzen, R., Kimberger, O., Kletecka-Pulker, M., Atanasov, A. G., & Willschke, H. (2021). Virtual and Augmented Reality Applications in Medicine: Analysis of the Scientific Literature. Journal of Medical Internet Research, 23(2), https://doi.org/10.2196/25499