Reconsideration of Ouija Board Motion in Terms of Haptic Illusions (Ⅲ) -Experiment with 1-DoF Linear Rail Device-

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1 Reconsideration of Ouija Board Motion in Terms of Haptic Illusions (Ⅲ) -Experiment with 1-DoF Linear Rail Device- Takahiro Shitara, Yuriko Nakai, Haruya Uematsu, Vibol Yem, and Hiroyuki Kajimoto, The University of Electro-Communications, Japan Abstract The Ouija board is a game associated with a type of involuntary motion called ideomotor action. We sought to clarify the conditions under which Ouija board motion occurs, by comparing visual and vibrotactile cues. We hypothesized that the ideomotor action of the Ouija board is caused by two factors: 1) visual and haptic movement cues, which lead to user movement, and 2) interactions between multiple players, which enable each user to feel that she/he is not responsible for the movement. In this paper, we describe our 1-degree of freedom linear rail device, and detail two experiments conducted to test our hypotheses. In the first experiment, we investigated whether vision and tactile motion cues would cause ideomotor action when presented to a single individual. We found that simultaneous presentation of visual motion and tactile illusory forces is important for the occurrence of ideomotor action. In the second experiment, we investigated whether the ideomotor action was larger when there were two players. We found that the amount of displacement was reduced compared with the first experiment. Thus, we could not confirm the effect of multiple users on ideomotor action in the Ouija board game. I. INTRODUCTION The Ouija board is a game that can be played by multiple players, using a flat board marked with letters and numbers, and a planchette, which is a small heart-shaped object that is placed on top of the board. The players place their fingers on the planchette, ask questions, and watch as the piece mysteriously moves across the board to point to various letters or numbers in response. Several variations can be found worldwide, such as Kokkuri-san in Japan (Figure 1). The movement of the game piece is considered to be a type of ideomotor action, i.e., a psychological phenomenon wherein a person makes movements unconsciously [1]. Typically, the Ouija board involves multiple players, and the movement might result from the cooperation of all players. However, no single person thinks that they are responsible for the movement, and each individual assumes that the planchette is moved by others (including possible *Research supported by JSPS KAKENHI Grant Number JP15H Takahiro Shitara is with the University of Electro-Communications, 1-5-1, Chofugaoka, Chohu, Japan ( shitara@ kaji-lab.jp). Yuriko Nakai is with the University of Electro-Communications, 1-5-1, Chofugaoka, Chohu, Japan ( yuriko@ kaji-lab.jp). Haruya Uematsu is with the University of Electro-Communications, 1-5-1, Chofugaoka, Chohu, Japan ( uematsu@ kaji-lab.jp). Vibol Yem is with the University of Electro-Communications, 1-5-1, Chofugaoka, Chohu, Japan ( yem@ kaji-lab.jp). Hiroyuki Kajimoto is with the University of Electro-Communications, 1-5-1, Chofugaoka, Chohu, Japan ( kajimoto@ kaji-lab.jp). spiritual beings). Hence, this phenomenon can be considered to be a type of haptic illusion that induces motion in individual users. In our first study of the Ouija board phenomenon [2], we described the contribution of visual, force, and vibration cues. However, the friction and inertia generated by the device hindered characterization of the illusion. In our second study [3], we developed a new 1 degree of freedom (DoF) device with lower friction and inertia for studying this phenomenon. In this paper, we briefly introduce our developed device, and then describe two experiments designed to test how the Ouija board phenomenon is affected by visual and haptic movement cues, as well as interactions between players. Figure 1. Ouija board (Kokkuri-san) phenomenon: ideomotor action II. RELATED WORK Several studies have shown that tactile cues can produce illusory force. Amemiya et al. [4] and Rekimoto [5] presented tractive force via a simple device that uses asymmetric vibration. Skin traction may also be felt as an external force [6] [7] [8] [9]. However, a typical illusion of force by vibration requires continuous asymmetric vibration, which is not the case in the Ouija board situation. Furthermore, haptic force illusions do not explicitly accompany motion. Therefore, although they might play a part, other factors contribute to the Ouija board phenomenon. The hanger reflex is a haptic force illusion that explicitly accompanies involuntary motion [10] [11] [12]. The typical hanger reflex is an involuntary rotational movement caused by deformation of the skin at particular locations on the head, and users typically report feeling as if an external force is rotating their head. The hanger reflex is thought to arise from shear deformation of the skin [13], which is known to contribute to force sensations [14] [15] [16]. However, while the hanger

2 reflex requires users to wear an elastic ring around their head, in the Ouija board game, the users freely place their hands on the planchette. Thus, although we cannot fully rule out the possible contribution of constant tangential skin deformation, we do not consider it to be a main factor in the Ouija board phenomenon. We hypothesize that the Ouija board phenomenon is caused by cues regarding illusory movement (not necessarily force ), which induce actual movement. In other words, users feel vibration associated with stick and slip, as well as visual movement, and these cues are regarded as self-movement. Users then involuntary move their hands to resolve inconsistency between the motion cues and their actual physical status. The existence of other players could be another key factor, in that the presence of others could render the agency of the movement ambiguous. In summary, we hypothesized that there are two main factors contributing to ideomotor action in the Ouija board game. (1) Visual or haptic movement cues prior to actual motion of the finger; and (2) A context that shows the existence of other individuals to obscure the agency of movement. In the case of the Ouija board, this context is achieved explicitly by the existence of the other players, or by a belief in a spiritual being. III. 1-DOF LINEAR RAIL DEVICE We developed a fingertip-type haptic device that can give haptic movement cues with minimal inertia and friction (Figure 2) [3]. A visual display was placed on top of the haptic device to present visual information that was synchronized with finger motion (Figure 3). Figure 3. System Setup A. Hardware evaluation We conducted a hardware evaluation to measure the frequency characteristics of our device. We measured amplitude and acceleration amplitude with 10, 20, 40, 80, 160, 320, 640 Hz sinusoidal waves. To learn the open-loop characteristics, we did not apply any feedback. We used pulse width modulation to apply a sinusoidal signal to the motor. Figure 4 shows the amplitude and acceleration data. The acceleration was calculated by multiplying the amplitude with the square of the angular frequency. We found that the amplitude of the vibration was slightly below 1 mm at 40 Hz, and around 0.1 mm at 160 Hz and 320 Hz, which are well above the detection threshold of the human hand [17]. As we sought to present tiny cues for finger movement in our experiment, the system performance was deemed sufficient. Figure 2. 1-DoF linear rail device The device comprises two DC motors (MAXON Inc., 4.5 W, RE16) that pull strings connected to a round planchette upon which the users place their fingers. The motors can present traction force and vibrotactile stimuli, which are controlled by a microcontroller (mbed NXP LPC1768, ARM Holdings). We used one motor encoder to measure finger position (the resolution of the encoder was 0.03 mm in terms of the amount of wire displacement), and a linear rail (LS877, THK CO., LTD, with a maximum displacement of 24 mm on each side) to reduce friction and confine the movement to one dimension. Figure 4. Frequency characteristics of the device IV. EXPERIMENT I A. Experiment Outline We tested whether the ideomotor action of the Ouija board could be generated in one user, given visual and haptic motion cues. All experiments were approved by the ethics committee of the University of Electro-Communications.

3 B. Experimental conditions We recruited six participants from our laboratory (five males, one female, 21 to 33 years old, five right-handed, one left-handed). The participants were instructed to place the index finger of their right hand on the finger rest of the device. We generated four haptic cue conditions: 1. Vibration with left shift, 2. Vibration with right shift, 3. Symmetric vibration, 4. No vibration. In all conditions, the stimulus was presented for 6 seconds. In conditions 1 and 2, we aimed to generate the sensation that the finger was sliding by presenting a movement that simulated a stick-slip phenomenon. As shown in Figure 5, the vibration had a 25-ms, 1-mm rising slope, compounded with a 100-Hz sinusoidal wave to simulate stick-slip. Then, in the following 25-ms, the planchette moved back to its original position. We strictly controlled the position of the planchette during this 50-ms process (otherwise, the planchette might automatically move in one direction as a result of asymmetric vibration). We determined the amplitude, duration, and frequency that best produced a natural stick-slip feeling. In Condition 3, we presented a 100-Hz sinusoidal wave with gradual rise and fall amplitude for 100-ms (Figure 5). The gradual rise and fall were intended not to provide any directional cues. In Condition 4, we presented no tactile stimulus, and this acted as a control condition. In conditions 1 through 3, the presentation cycle of the vibration was randomly set to range between 0.5 and 1.0 second. Figure 6. Visual conditions Combinations of the four haptics conditions and the two visual conditions rendered eight conditions in total. Each combination was presented three times, for 24 trials in random order. We instructed participants to look only at the display. The arms of the participants were hidden by a cloth. Auditory cuing was blocked by the presentation of white noise from headphones. C. Experimental procedure Figure 7 shows an overview of the experiment. Before the measurement, to encourage the participants to attend to the finger shown in the image, we instructed them to place their fingers on the planchette and manipulate the planchette freely for 2 minutes. This enabled them to observe how the images of the coins moved synchronously with their fingers. The participants were instructed to attend to the image of the coin on the display and to relax their arms and not resist movement of the planchette during the experiment. They were asked to return their fingers to the position corresponding to the center of the screen before the start of each trial. Figure 5. Haptic conditions For visual stimuli, we used an LCD display. The surface of the screen was positioned 9.5-cm above the haptic device, as shown in Figure 3. We displayed a background image of the Kokkuri-san game board, and an image with a finger on a 10-yen coin. We prepared two conditions for visual stimuli (Figure 6): I. without visual motion, and II. with additional visual motion. In condition I, the image of the finger did not change regardless of the finger movements and the tactile stimuli. In condition II, we presented an image of the finger moving synchronously with the stimulus direction. For example, in haptics cue condition 1, a presented visual leftward motion of 1-mm was synchronized with the haptics cue, but the rightward back motion was not presented. Additionally, when the planchette was moved by the participant, this movement was added to the visual motion. Figure 7. Experimental setup D. Results and discussion The experimental results are shown in Figure 8. The horizontal axis represents the stimulus condition, and the error bars represent the standard deviation. The vertical axis represents the average amount of displacement of the finger position in the stimulus direction. For example, in the Left Vibration condition, the left direction was a positive value. Regarding the Symmetric Vibration and No Vibration conditions, the direction of the visual stimulus was regarded as positive (in the condition without visual motion, we averaged the absolute value of finger displacement). Figure 9 shows the average amount of displacement when a weight of 30 g, approximately equal to that of one finger, was placed on the

4 planchette. As shown in Figure 9, we confirmed that our haptic cues produced little physical movement in the planchette. A 2 (visual stimuli) 4 (tactile stimuli) repeated measures ANOVA indicated main effects of the visual (F(1, 5) = 5.890, p < 0.05) and tactile stimuli (F(3,15) = 2.992, p < 0.05). No significant effect was observed for the interaction between the visual and tactile stimuli. V. EXPERIMENT II A. Experiment Outline We investigated how ideomotor action in the Ouija board phenomenon would be affected when two people participated in the game, instead of a single user. B. Experimental Conditions and Procedure Figure 10 shows the experimental setting. We recruited the same participants as in Experiment Ⅰ. Each participant conducted the experiment twice as part of two different user pairs. The experimental conditions and procedure were the same as in Experiment Ⅰ. Figure 8. Comparisons of mean finger displacement (positive stimulus direction) Figure 10. Experimental setup Figure 9. Displacement when a weight (30 g) is placed on the planchette (positive stimulus direction) We confirmed that participants made larger finger movements when exposed to a combination of visual and tactile motion cues, whereas large movements did not arise from the visual cue alone or the visual cue with symmetric vibration. These data confirm our first hypothesis, that visual or haptic movement cues would elicit actual motion of the finger in the Ouija board phenomenon. In our second experiment, we tested the effects of the presence of multiple players in the Ouija board situation, using the same experimental conditions as Experiment Ⅰ. This enabled us to test our second hypothesis, that a context in which users are aware of the existence of others could obscure agency of movement, and thus contribute to the Ouija board phenomenon. C. Results and discussion The experimental results are shown in Figure 11. The horizontal axis represents the stimulus condition, and the error bars represent the standard deviation. The vertical axis represents the average amount of finger position displacement towards the stimulus direction. A 2 (visual stimuli) 4 (tactile stimuli) repeated measures ANOVA indicated main effects of visual stimuli (F(1, 5) = 7.101, p < 0.05), but not tactile stimuli. The interaction between the visual and tactile stimuli was significant (F(3, 15) = 3.526, p < 0.05). Bonferroni post-hoc test revealed a significant difference between the visual conditions for the Left Vibration trials (p < 0.05). We also found significant difference between the visual conditions for the Right Vibration trials (p < 0.05). Figure 11. Comparisons of mean finger displacement (positive stimulus direction)

5 We found that, compared with Experiment Ⅰ, displacement was reduced for both the Left Vibration and Right Vibration conditions when there were two users. In addition, under the No Visual Stimulus condition, the participants moved their finger in the direction opposite that of the haptic stimulation. This suggests that that the existence of the other player enabled users to unconsciously resist the haptics cue, although the visual cue was still effective. The results of this experiment should be interpreted with consideration of certain limitations. First, the same participants took part in Experiments I and II, giving rise to the possibility of a learning effect. The participants in this experiment were also members of our laboratory, and may have been familiar with the haptic and visual cues. Finally, our sample size was small. VI. CONCLUSIONS Our goal was to clarify the conditions under which Ouija board motion occurs, by comparing visual and vibrotactile cues. In this experiment, we used a 1 degree of freedom (DoF) Linear Rail Device, which we previously developed to investigate ideomotor action with minimal friction and inertia. In Experiment Ⅰ, we investigated whether visual and tactile stimuli would cause ideomotor action in one user engaged in the Ouija board game. Our result showed that simultaneous presentation of visual and tactile stimuli was important for the occurrence of ideomotor action. In the conventional presentation of pseudo force via vibration, a continuous asymmetric acceleration is used to provide information about force. However, in the present study, we sought to elicit the sensation of movement by presenting visual and tactile stimuli, thus inducing unconscious movement. In other words, we provoked the user to generate movement by presenting stimuli indicating that the planchette had already moved. In Experiment Ⅱ, we examined whether two users would have a stronger influence on ideomotor action, using the same experimental environment as in Experiment Ⅰ. We found that the amount of displacement was actually reduced compared with the first experiment, and that the haptic cues produced a negative result. However, our study had a limited number of participants and a possible learning effect, so we could not make conclusions regarding the effect of multiple players. In future work, we plan to conduct experiments with a larger number of completely naive participants. In addition, we will provide questions to ask, as with the actual Ouija board game, and evaluate the effect of such questions. Furthermore, we plan to develop a device with two degrees of freedom, to enable us to conduct experiments with a level of realism that is closer to an actual Ouija board. REFERENCES [1] Stock, A., Stock, C.: A short history of ideo-motor action. Psychological Research 68, 2-3, (2004) [2] Shitara, T., Nakai, Y., Uematsu, H., Yem, V., Kajimoto, H., and Saga, S.: Reconsideration of Ouija Board Motion in Terms of Haptics Illusions. Proceedings of Euro Haptics Conference (2016). [3] Shitara, T., Nakai, Y., Uematsu, H., Yem, V., Kajimoto, H., and Saga, S.: Reconsideration of Ouija Board Motion in Terms of Haptics Illusions (II) -Development of 1-DoF Linear Rail Device-. Proceedings of AsiaHaptics Conference (2016) [4] Amemiya, T., Gomi, H.: Distinct pseudo-attraction force sensation by a thumb-sized vibrator that oscillates asymmetrically. Haptics: Neuroscience, Devices, Modeling, and Applications Lecture Notes in Computer Science 8619, (2014) [5] Rekimoto, J.: Traxion: A tactile interaction device with virtual force sensation. Proceedings of the ACM Symposium of User Interface Software and Technology, (2013) [6] Yem, V., Kuzuoka, H., Yamashita, N., Ohta, S., Takeuchi, Y.: Hand-skill learning using outer-covering haptic display. 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Journal of Orthopaedic Research 22, (2004) [17] Brisben, A.J., Hsiao, S., Johnson, K.O.: Detection of Vibration Transmitted Through an Object Grasped in the Hand. Journal of Neurophysiology 81, (1999) ACKNOWLEDGMENT This work was supported by JSPS KAKENHI Grant Number JP15H05923 (Grant-in-Aid for Scientific Research on Innovative Areas, Innovative SHITSUKSAN Science and Technology ).