Keywords

1 Introduction

1.1 Background

In virtual environments, it is known that synchronizing the actions of an avatar with the operator causes a change in the operator’s self-perception, resulting in a change of behavior. This phenomenon is called the Proteus effect [4, 5]. It has been clarified that the reason why this change occurs is because the operator infers the attitude and role expected of the avatar from its appearance [1] (e.g. When the operator uses an avatar that is expected to behave attractively, the operator’s behavior becomes attractive.). Also it has been clarified that this phenomenon lasts for some extent even after stopping using the avatar [4]. Riva [3] clarified that self-perception can be distorted and malformed when accepting the improper evaluation from others and become locked. So, the Proteus effect is looked forward to a treatment method for such mental diseases.

1.2 Related Works

Nicks [1] investigated whether opinions on the cause of sexual assault will change in accordance to how revealingly dressed the used avatar is. The results showed that, more participants using avatars that were less revealingly dressed stated that the cause of sexual assault is the revealing dressing of the victim. Nicks assumed that these opinions were a result of self-defence, as the participants reflected on the avatars as “themselves” and did not want to be subject to sexual assault. Konstantinas [2] used three kinds of avatars, wearing a formal suit, dressed in casual wear, and hands without a body, to investigate how the avatar’s appearance affects how the participants play the drum. The results revealed that whether or not the avatar is assumed “suited” for the task has more influence on the change of behavior than simply inferring the avatar’s behavior. In addition, due to more sense of body ownership leading to an increase of drumming performance variety, the sense of body ownership found to have a significant effect on the magnitude of the occurring Proteus effect. This body-ownership is a state in which a particular body is perceived as one’s own body. It is known that this can transfer to objects other than your body when synchronized with a tactile stimulus. According to these studies, the Proteus Effect affects real people if the motion of the avatar and the motion of the operator are synchronized with movement or tactile information.

1.3 Purpose

Although self-perception can be changed in Proteus Effect, physical sensations such as tactile sense and vision stays the same such as tactile sense and vision does not change (e.g. Even if you use a muscular avatar in virtual space, it doesn’t mean you actually gain strength in real space). This, together with a change in the perception of physical sensation due to a change in self-perception may cause an illusion. Therefore, there is a possibility that a physical representation that causes improper self-perception may cause a malformation of physical sensations by treatment actions such as psychological rehabilitation. As a result of changes in the evaluation of physical senses, there may be a possibility of the appearance of new psychological diseases such as objects feeling heavier than they actually are. So, in this research, we aim to investigate the effects of changed self-perception due to the Proteus Effects on the evaluation of physical senses by examining the influence of an avatar’s arm thickness on the evaluation of weight in a VR space.

2 Method

In this research, a system as shown in Fig. 1 was constructed. The flow of data is explained below.

We used Leap Motion to track and acquire the avatar operator’s hand skeleton information. The skeleton Information is sent to unity to update the avatar’s movement. To track other information such as the position of the weight held by the operator, we used a web camera. The image information from the web camera is sent to Unity, then image processing is performed to binarize the colors in the image using binary preset thresholds. Based on the processed image data, the movement of the ball is updated in Unity. Finally, the constructed VR space is drawn with oculus (Fig. 2).

Fig. 1.
figure 1

System overview

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Fig. 2.
figure 2

Avatars in each condition (left: C1, right: C2)

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2.1 Design

In order to investigate the change in the subjective evaluation of the weight caused by the avatar’s arm’s appearance, the experiment was conducted under the following C1 and C2 conditions.

  • C1: Avatar that seems to be strong with a thick arm

  • C2: Avatar that seems to be weak with a thin arm

2.2 Procedure and Hypothesis

Experiments were conducted with 25 university students subjects, according to the following procedure under C1 and C2 conditions. After that, we compared the result.

  1. 1.

    Memorize reference weight in HMD turned off

  2. 2.

    Turn on HMD

  3. 3.

    Synchronize work to make the Proteus effect occur

  4. 4.

    Compare the weight to the reference one

  5. 5.

    Evaluate in 7 steps

We hypothesized that operator will evaluate more heavy than the reference under C1 and more light than the reference under C2.

Fig. 3.
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The evaluation of weight

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3 Results and Discussion

An average t-test with a pair of specimens was performed for the difference between the average of the evaluations of C1 and C2. The results are shown in Fig. 3. There was a significant difference in the change in the subjective evaluation of the weight due to the change in thickness of the t avatar’s arm.

The change in the evaluations can be explained as follows. First with the HMD turned off, the weight is memorized as body knowledge based on the participant’s mental body representation the real space. Next, after turning on the HMD and performing the synchronization task in the VR space, operators perceived the avatar’s arms as their own arm. After that, by evaluating the arm of the avatar that he is manipulating, the Proteus effect occurred, and the participants mental body representation changed (the arm of avatar is evaluated to be more muscular than their actual arm). Nonetheless, the participants evaluated a weight that is the same weight as the previous one in VR space. Finally, operators had an illusion that the weight they have now is heavier than the reference.

4 Conclusions

In this research, we investigated the influence of the change in self-perception by the Proteus effect on subjective evaluation of weight in VR space. In the experiments, participants made an illusion in the perceiving of physical sensation due to a change in self-perception. Therefore, in environments where the Proteus effect occur, there is a possibility that the appearance of the avatar may cause an illusion on the evaluation of physical sensations, so the appearance of the avatar must be selected carefully. Further investigation on how to reduce the duration and magnitude of the illusion of physical sensations is needed.