IROS2019国际学术会议论文集0367

Torso-mounted Vibrotactile Interface to Experimentally Induce Illusory Own-body Perceptions Atena Fadaei Jouybari1,2, Giulio Rognini1, Masayuki Hara3, Hannes Bleuler2and Olaf Blanke1 AbstractRecent developments in virtual reality and robotic technologies have allowed investigating the behavioural and brain mechanisms that grounds self-consciousness in the multi- sensory (e.g. vision and touch) and sensorimotor processing of bodily signals. Yet, previous technological solutions to apply tactile stimuli for body illusion induction limit participants movements, do not allow for stimulations in dynamic environ- ments (e.g., the subject walking), and can hardly be integrated into real-life settings and complex, interactive, virtual reality environments. Here, we present the development and fi rst validation of a new semi-wearable haptic system, based on vibration technology, to induce a range of bodily illusions that are of relevance for research in psychiatry. This is a fi rst step towards the development of wearable haptic systems able to administer touch and induce specifi c bodily illusions under dynamic conditions and in real-life settings. I. INTRODUCTION Recent experimental evidence from neurology and cog- nitive neuroscience has shown how the multisensory and sensorimotor integration of bodily signals provide the basis for bodily self-consciousness (BSC) - the non-conceptual and pre-refl ective representation of body-related information 13. Thus, when experimentally exposed to confl icting multisensory bodily cues about the location, appearance, and synchrony of ones own body signals, participants are prone to report signifi cant alterations of their bodily experience (illusory own-body perceptions). For example, in the rubber hand illusion synchronous stroking of a seen rubber hand and ones own real hand (hidden from view) induce illusory ownership over the fake hand and bias the perceived location of ones own hand towards the rubber hand (proprioceptive drift) 4. Through the use of virtual reality technology, and by applying synchronous tactile stimuli on the participants torso and a seen avatar, these manipulations have been also extended to the full body (full body illusion) 5, 6. More recently, the development of MRI-compatible robotic technology has allowed performing these paradigms in MRI environments, thereby enabling precise time-delay, as well allowing the investigations of the neural mechanisms of these illusions 7. Another important line of work has used sensorimotor (in- stead of multisensory) manipulations of ones bodily signals 1Ecole Polytechnique F ed erale de Lausanne (EPFL), School of Life Sci- ences, Brain Mind Institute, Center for Neuroprosthetics, Campus Biotech H4, Chemin des Mines 9, CH-1202 Genve Switzerland 2Ecole Polytechnique F ed erale de Lausanne (EPFL), School of Engi- neering, Laboratory of Robotic Systems, Station 17, CH-1015 Lausanne, Switzerland 3Graduate School of Science and Engineering, Saitama University, 338- 8570 Saitama, Japan to induce systematic changes in BSC. Thus, in the tactile rubber hand illusion, blindfolded participants are guided by the experimenter to touch a fake hand, while synchronously receiving the touch on their other real hand 8. This results in the subjective illusion of touching ones hand (illusory self- touch) and induces a bias in the localization of the touched hand that is perceived closer to the touching hand. Recently, this sensorimotor paradigm has been adapted to the full body. Hence, Blanke et al. used a robotic system to apply sensori- motor manipulations between hand and torso of blindfolded participants 9. Participants were asked to perform voluntary tapping movement with both hands, by using the leader hap- tic device placed in front of them, and received synchronous or asynchronous tactile feedback on their back. Similarly, to the tactile rubber hand illusion, in the synchronous condition, participants reported the illusory experience of touching their back (illusory self-touch). Importantly, during asynchronous stimulation, participants not only reported a reduced self- touch experience but also the illusory sensations of having someone behind them (Presence Hallucination, PH) and felt touched by someone (passivity experience), comparable to experiences reported by neurological and psychiatry patients 10. In spite of the recent achievements in robotic manipulation of tactile stimuli during several bodily illusions 7, 9, haptic technology for BSC is relatively underdeveloped, compared to the advances in auditory (e.g. sound special- ization, 3D audio, etc.) and visual stimulations (such as VR/AR technology, stereoscope view, etc.). For instance, the usage of the leader-follower robotic system described in the PH study 9 is limited to the laboratory environment and to stationary conditions of participants (i.e., the participants cannot walk during stimulation), while the emerging visual 11 and auditory technologies 12 allow researchers to handle various multisensory in-congruency with small-scale, portable setups and in complex and dynamic environments. We here focus on the development of wearable and portable tactile stimulation interface for the human torso. This is because torso-related tactile signals have been shown to be crucial in manipulating global aspects of bodily self- consciousness and the PH in particular 3, 13. In this article, we designed a new torso-mounted vibro- tactile display to investigate illusory own-body perceptions, and particularly PH and passivity experiences, based on the paradigm proposed by Blanke et al. 9 (experiment 2). We fi rst conducted a feasibility study and deployed the novel semi-wearable setup in experimentally inducing bodily illusions for healthy participants. In addition, in order 2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) Macau, China, November 4-8, 2019 978-1-7281-4003-2/19/$31.00 2019 European Union6204 Follower robot Leader haptic interface Tactile feedback (a) Classical manner Leader haptic interface Vibrotactile feedback Vibrator Torso-mounted vibrotactile interface (b) Proposed manner Fig. 1: Schematic views of classical and proposed experi- mental setups and environments for experimentally inducing PH and relevant bodily illusions. to characterize the new vibrotactile garment, we combined the PH experiment with additional vibrotactile perception tasks/questionnaires. II. NEWWEARABLE SETUP TO INDUCE BODILY ILLUSIONS Figure 1a depicts a schematic view of the experimental environment, deployed in the study 9 (experiments 2 and 3). The setup comprised two robots, the leader haptic device, Geomagic Touch, and a three degree-of-freedom (DOF) follower robot. The position of the follower robot was controlled with the leader haptic device, causing a complete coincidence between the movements of the two devices. Participant moved the leader haptic device with the right index fi nger (a 3D printed fi nger place, Figure 2b, was used to fi x participants fi nger at the leader haptic interface), which operated the movements of the follower robot that provides touches to the participants back. The experimental setup in the current study is the modifi ed version of the two-part robotic system, employed in the study 9 (experiment 2 and 3). Figure 1b represents the schematic view of the proposed experimental condition. In the new experimental arrangement, the follower robot was replaced with a torso-mounted vibrotactile interface (see Figure 2a), to provide the vibration stimulus on the participants back. The vibrotactile suite consists of two arrays of vibrators, with a plastic-like covering. Each array had three coin-shaped, Eccentric Rotating Mass (ERM) vibrators (310-118, Preci- sion MicroDrive; frequency: 200-250 Hz; amplitude: 0.8-1.3 g), with in-plane vibrations. An inter-vibrator distance of 8 cm was chosen to be bigger than the 2-point discrimination threshold for the back 14. A pilot study confi rmed that using three vibrators on each vertical array are suffi cient. A chest belt was employed to locate vibrator interfaces on the participants upper back. There were specifi c belts for women and men. The woman belt was specially shaped to conform to the chest, ensuring correct fi t and fi rm support. Two vibrator arrays mounted vertically on the belt with a fi x horizontal distance of 15 cm for almost all participants (for three participants, two vibrator arrays were located closer, because of their small size). This distance was chosen based on the average distance between the shoulder blades. Figure 2c represents the arrangement of vibrators on the back and vibrators numbering. A wireless micro-controller board, embedded in 3D printed box, were deployed to run vibrators through custom software. On the leader haptic device, a single coin-shaped ERM vibrator, similar to the back vibrators, was added to the end of the fi nger placement to provide a vibration stimulus on the fi ngertip (see Figure 2b). The fi ngertip vibrator was controlled by an Arduino and works congruently with back vibrators. In contrast to the follower robot 9, with continuous workspace, the wearable actuator suite can only provide six discrete vibrotactile stimuli on the back. To assess spatial correspondence between continuous hand workspace and discrete back workspace, the hand exploration area was divided into 6 different smaller regions according to the vibrators arrangement on the back. Moreover, a virtual wall with a stiffness of 0.5 N/mm was provided at the leader haptic device, to administer a virtual wall, when the participant touches his/her back. Thus, depending on the region that the participant touches the virtual back with his/her index fi nger, the corresponding vibrator activates on the back. Custom Graphical User Interface (GUI) written in Visual C+ (Microsoft) was developed to link the leader haptic device and vibrotactile actuator suite and to control the experiment fl ow. III. SETUP CHARACTRIZATION AND FEASIBILITY STUDY A. Experimental design 1) Experimentally induction of bodilly illusions: The be- havioral experiment was designed to investigate the possibil- ity of inducing the PH and passivity experiences in healthy subjects by providing vibrotactile-motor signals. Similar to our previous study 9, the effect of synchrony (synchronous (SYNC) vs. asynchronous (ASYNC) were investigated, while the force feedback at the fi ngertip of the moving hand was provided in both conditions. This was done to provide a virtual wall when participants touched their back 6205 d jjjjjj a c b (b) Finger placement Vibrator Chest belt Covers Connecting PCBs (a) Torso-mounted vibrotactile interface 8 cm (c) Vibrators arrangement 15 cm 1 2 3 4 5 6 CalibrationFirst-PLTSYNC ASYNC SYNC ASYNCSecond-PLT 1.5 min 2 min 70 trials 2 min 2 min 2 min 70 trials Poking (d) Experiment flow Fig. 2: Novel experimental setups and procedure to artifi cially induce PH and related bodily illusions. (during SYNC or ASYNC conditions). In the original study, Blanke et al. 9 found that the force feedback did not have a signifi cant effect on inducing PH, yet pilot testing showed that participants tend to report higher PH when force feedback was provided and the original study 9 also found changes in self-location depending on force feedback. In addition, to reduce habituation effects and decreases in tactile perception, we used a variable delay of 500100 ms, instead of the fi xed delay used in 9. To assess subjective changes in own body perception of participants during the experiment, a 4-item questionnaire (i.e. Bodily illusions questionnaire), adopted from 9 (ex- periment 2), was proposed to participants at the end of each experimental condition. Self-touch: “I felt as if I was poking my back.” Passivity: “I felt as if someone else was poking my back.” PH: “I felt as if someone was standing close to me or behind me.” Control: “I felt as if I had 3 bodies.” Participants were asked to rate on 7 points Likert scale, how strong they agreed with each item (0 = not at all, 3 = not certain, 6= very strong). In addition, a dedicated questionnaire to assess tactile perception (called as User experience questionnaire) was used during the poking phase, after another pair of SYNC and ASYNC blocks, to assess the quality of tactile stimuli and the garment. Uniform, vibrotactile sensation (UVS): “I felt the same strength of vibration in the different parts of my back.” System performance (SP): “The tactile stimuli that I felt on my back matched with my anticipation from the hand exploration task.” Comfortability: “I felt as if someone was standing close to me or behind me.” 2) Tactile task: In order to characterize the vibrotactile setup and better understand human vibrotactile perception on the upper back, we designed and administrated a Point Localization Task (PLT). In this task, subjects received one vibrotactile stimulus at a time, and they were asked to indicate where they perceived the tactile stimuli on their back. Responses were given with a handheld keypad (prior to the PLT task, they had been informed about the arrangement of vibrators on their back (see Figure 2c). That is, the PLT was used to investigate participants absolute vibrotactile localization acuity 15. The PLT task was repeated during the experiment, once before and once after the poking task, to assess possible changes in tactile perception throughout the experiment. B. Participants 22 healthy participants (15 females; age range: 18-32 years; average age (SD): 25.6 years (3.9 years) participated in the experiment. All participants were right-handed, had no history of a neurological or psychiatric disease and were na ve to the goal of the study. In addition, participants with a wound or scar on their upper back were excluded since the former injury on the back could potentially infl uence sensitivity to vibrotactile stimuli. Informed consent was obtained, after all instructions on the experiment were given to participants, and their questions answered. All participants received fi nancial compensation for their participation. The research was conducted in accordance with the Helsinki Declaration. C. Procedure Prior to the experiment, all participants were asked to wear a T-shirt and the vibrotactile interface. The experimenter helped them to properly locate the vibrator arrays on their back (two upper vibrators on each array must be located on two shoulder blades and the rest vibrators were placed below). The experiment consists of three different sessions (see Figure 2d): calibration task, PLT task (the First-PLT and the second-PLT) and the poking task. 1) Calibration: Participants had to complete the vibro- tactile calibration task while they were listening to white noise through headphones. During the calibration task, they received randomized, vibrations on their back (for a constant duration of 270 ms followed with 1 s time interval between each two successive vibrations) for a period of 45 seconds 6206 and later they verbally answered the following question: ”Did you receive uniform vibrotactile sensation all over your back and if not where was the weakest and strongest points?”. Depending upon participants responses, the exper- imenter applied the following modifi cations: 1) re-adjusting the location of vibrotactile interface on the participants back, 2) changing the intensity of weaker or stronger vibrators (following participants request, the intensity of two upper vibrators, which were located on each side shoulder blade was decreased between 33% to 55%), 3) utilizing another chest belt on top of the vibrator belt to ensure that all vibrators were well in contact with the skin (for most of the subjects, especially medium and small size subjects the second belt was used ). The calibration session was repeated until participants confi rmed uniform vibrotactile perception on their back (in average, there were 2 calibration sessions per subject). Participants were asked to keep standing during the whole experiment to avoid any changes in calibration. 2) PLT:In the PLT, participants received a pseudo- random, single vibration stimulus on their back, and were asked to indicate the location of the perceived vibration by specifying the number of the corresponding vibrator by a numeric keypad (see Figure 2c). No feedback about their performance was given to participants during the task. Moreover, to reduce task complexity, they were instructed to hold the keypad so they could see the numeric keypad buttons in a sequence matching the vibrators numbering on the back. Catch trials were added as a control trial to assess the extent to which participants responded to perceived vibrotactile stimuli, rather than using other response strategies. Each of the six location was stimulated 10 times resulting in a total of 70 trials. The vibrators were turned on for 270 ms and followed with a random interval in the range of 2000250 ms. For each individual trial, participants response was recorded by the software. During the task, participants wore headphones playing white noise to mask the sound of vibrators. The white noise intensity was adjusted for each participant in order to have complete acoustic isolation. All participants tried a training session, similar to the main task but shorter, around 1 min, to learn how to respond to vibration with the keypad. To explore any changes in tactile perception, the PLT task was repeated, along with the experiment, before (First-PLT) and after (Second-PLT) the poking task. 3) Poking: During the poking task, similar to the study 9 (experiment 2), participants were asked to do poking movements using leader haptic device and receiving vibra- tions on the back through the vibrotactile suite, while they were blindfolded, sound isolated, and standing in front of the leader robot. In the