Body ownership, which is the feeling that one’s body part belongs to oneself, and agency, which is the sense of being able to control one’s own body part, can be felt towards fake body parts and those depicted by computer graphics. As part of an attempt to transfer self-body awareness to fake body segments, we investigated whether body ownership and agency are felt towards two visible left hands in an immersive virtual reality environment. One of the two hands shown through virtual reality goggles spatially matched the unseen actual hand. The other hand was fake and displayed at either the 10-cm lateral or medial side of the position of the actual hand. These two left hands moved synchronously with the actual left hand. Participants completed a behavioral test and questionnaire after adapting to the two left hands. In the behavioral test, participants accessed randomly emerging spheres using the seen hands as fast as possible. They used the fake hand to touch a sphere when it appeared near the fake hand 41% of the time when the fake hand was displayed at the medial position of the actual hand. The results of the questionnaire suggest that agency was experienced for the two visible left hands for this condition. By contrast, body ownership was felt mostly against the displayed hand that was spatially consistent with the actual hand. These findings indicate that although agency can be simultaneously felt for two seen left hands, body ownership is felt only for either of the two visible left hands.

Recent 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 environments (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 first 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 first step towards the development of wearable haptic systems able to administer touch and induce specific bodily illusions under dynamic conditions and in real-life settings.

The rubber hand illusion (RHI) is a bodily illusion that a fake rubber hand is felt as if it was one's own hand when both the hands are synchronously stimulated. Also, it is well-known that people can experience the RHI when the movements of the visible fake and invisible real hands are synchronized. However, underlying mechanism of the RHI and relationship between action and body ownership are still open questions. Based on the RHI paradigm, the present paper discusses how the agency of a body part affects the sense of body ownership at the other body part. In this study, we examined if a simple up-and-down action of right index finger induces the RHI to left hand which was kept still by using virtual reality and robotics technologies. Our experimental results indicated that the action of the right index finger allowed the embodiment of the virtual hands at both the right and left hands. This implies that only a simple action of a body part increases the sense of body ownership at the other body part.

This paper introduces an approach for manipulating bodily self-consciousness, in particular, senses of body ownership and illusory self-touch by using a robotic/haptic technology. This study especially focuses on the rubber hand illusion (RHI). In the classic RHI paradigm, an invisible participant's hand and a visible fake rubber hand are manually stimulated by an experimenter. However, our approach, which is termed active self-touch, allows the participants to administrate the tactile stimulation with variable force feedback by using a robotic master-slave system. Three RHI experiments with active self-touch were performed to demonstrate the utility of the proposed approach for assessment of bodily self-consciousness. The embodiment of a fake hand was assessed with the classic RHI paradigm, and the RHI paradigm with somatic sensation was applied to examine the effect of variable force feedback on the sense of illusory self-touch. These experiments verified that active self-touch allows participants to experience the classic RHI. In addition, the results implied that the sense of illusory self-touch can be induced, even if force feedback is absent in the dynamic self-touch condition, and that illusory sensation is easily modulated by variable force feedback during quasi-static self-touch rather than during dynamic self-touch. These findings suggest that our proposed approach has the potential to reveal relationships between action/haptic perception and the sense of body ownership.

Our previous study has proposed a novel approach with a robotic/haptic technology to tactile rubber hand illusion (TRHI) paradigm in order to open new discussions about the manipulation of human body-parts ownership. The results demonstrated that the use of master-slave system can cause the TRHI, enabling a unique condition-active self-touch. As an advanced approach, this study examines the effect of force feedback on the TRHI under the active self-touch. We hypothesize that appropriate force feedback plays an important role to determine our body-parts ownership, people would not experience the TRHI if the force feedback from a fake hand largely differs from the contact force on a real hand. This paper, in particular, discusses how the force feedback affects the TRHI under the active self-touch by variously changing force rendering on the master device.

This paper describes the system development of an admittance-controlled 2-dof haptic device using electrostatic motors. The unique point of the device is that all components including the motors and sensors are fabricated using non ferromagnetic materials to realize operation in a strong magnetic field. The device consists of an operation handle, two electrostatic motor units and two optical force sensors, and is an improved version of our previous development. The new device has stiffer platforms, improved force sensors, and newly fabricated driving electronics. The employed electrostatic motor is one of the strongest electrostatic actuators and can generate thrust force of several newtons. To operate a motor unit, two three-phase signals are required and they have to be amplified to over 1 kV. In our previous development, the signals were amplified by six large commercial amplifiers, which was not practical enough considering the portability of the system. This work developed an original driving electronics for the motor using Field Programmable Gate Array (FPGA) and step-up transformers to reduce the system size. The device was implemented on one of the major haptic toolkits, CHAI 3D. To be able to run sample impedance-type programs without any modifications, we implemented our device to behave like impedance-type on CHAI 3D.

This paper introduces a novel approach to the manipulation of body-parts ownership, using the tactile rubber hand illusion (RHI) paradigm. In the conventional studies on the RHI, participant's invisible hand and the visible rubber hand are manually tapped or stroked by an experimenter. Differently, in our approach, a bilateral master-slave system is applied to provide tactile stimulations in a novel interactive manner—active self-touch. Here, we present a 3-DOF master-slave system based on human self-touch characteristics and a validation experiment using an arranged version of the conventional RHI paradigm. In this new version, participants can contact with the rubber hand by manipulating the master device with their right hand and actively touch their own left hand through the slave device. The results demonstrate that the master-slave system can be successfully used to manipulate body-parts ownership, opening up the way to new studies concerning self-touch and body representation.

Haptic interfaces compatible with functional magnetic resonance imaging (fMRI) are finding increasing interest as a tool to explore the neural correlates of human motor control and related dysfunctions. To achieve safety and MR compatibility, such devices have mainly relied on unconventional actuation methods suffering from limited bandwidth and non-linearities. This has resulted in complex control and restricted their use in applications involving fine and dynamic interaction with the hand and fingers. To address these limitations, we propose a concept for a shielded high-performance actuation system to be located inside the MR room, evaluate the effectiveness of the shielding and perform detailed MR compatibility tests. A conventional electromagnetic actuator is located within a steel shield to prevent mutual disturbance with magnetic fields of the scanner, which, together with power and control hardware, is placed within a Faraday cage with only a fiber-optical USB link to the control room. Detailed compatibility tests show that disturbing dynamic electromagnetic fields generated by the actuation system are well below the detectable threshold of the scanner, and actuator performance is not degraded by the MR environment. In combination with a light and stiff cable or rod transmission, the presented actuator technology, providing high transparency and force bandwidth, paves the way for fMRI-based neuroscience studies, e.g., to investigate the fine motor control of hand and fingers.

Currently, the concept of ergonomically designed workplace using 3D graphic mannequins is gaining wide acceptance among the design engineers. However, predicting the human operational feeling level (i.e., comfort or discomfort level) during an ergonomic analysis of a virtual work situation is still in immature level. The current study is an attempt in that direction. This paper presents an approach that estimates the degree of comfort or discomfort felt by an operator during a lever manipulation task by using limb anthropometric and kinematic data. In this study, a haptic lever has been developed that emulates a lock-ball type lever action. Experiments were carried out with healthy male subjects under two different torque characteristics of the haptic lever. Using multiple regression analysis it has been found that the subjects operational feeling level can be estimated by means of shoulder flexion-extension angle and manipulability measure.

This paper describes the development of a 2-DOF electrostatic haptic joystick designed for neuroscience studies in an MRI/fMRI. The joystick is fabricated using non-magnetic materials and actuated by two high-power electrostatic motor units which produce various force fields in the horizontal plane. The electrostatic motor is a synchronous drive and thus the positioning of the joystick is achieved in an open-loop control. As for force sensing, a 2-DOF force sensor is developed using non-magnetic materials and optical fibers so as to measure interaction force with a user; hence, the haptic rendering is based on the admittance control scheme that respects the rule of force-in and position-out. The operation of both the actuators and force sensor respects non-magnetic principles. Thus, the haptic joystick into which these components are integrated is expected to have high MR compatibility, although the evaluation of the MR compatibility is beyond the scope of this paper. In this paper, the device performance is evaluated in the normal environment, which verifies the operation of the unique electrostatic haptic device.

Motion control algorithms were proposed for a 9-DOF finger-arm robot by using the finger manipulability obtained in a previous study. However, in the previous study, only methods for achieving unconstrained movement of the finger-arm robot were discussed. In this paper, the authors propose a novel method for having a finger-arm robot complete a constrained task by integrating impedance control with manipulability control of the finger. First, methods of applying the previous heuristic method to the passive impedance control and the active impedance control were developed; and experiments were performed to demonstrate the features. Then, an impedance control combined with the steepest ascent method to modulate the manipulability of the finger was proposed. The proposed method demonstrates a strong performance even when a dynamic external force is applied to the finger. By using the proposed method, the arm actively moves along a direction to effectively maintain the moving potential of the finger during both the unconstrained and the constrained tasks.

This paper describes the effect of Muller-Lyer illusion on a reaching movement just after the visual and haptic/kinesthetic cues are simultaneously presented. First, a standard experiment on this visual illusion is conducted by means of the most typical way so as to make sure that participants can experience this illusion; the result shows that all the subjects are deceived by the illusion figure as in many previous results. As the next step, the subjects are asked to physically trace one of three lines-normal line and lines with feathers of an arrow-with the same length displayed on an LCD. After a few traces, the line suddenly vanishes, and then the subjects retrace the invisible line based on only their memory and somatic sensations. During this task, we measure the trajectory of fingertip from a start to the goal using a motion capture system. The result indicates that the Muller-Lyer illusion dominantly affects the reaching task although the haptic/kinesthetic cue was also given just before the task. Thus, this result implies that the visual illusion affects the motion planning, which partly supports a planning-motion model.

This study attempts to make a compact humanoid robot acquire a giant-swing motion without any robotic models by using reinforcement learning; only the interaction with environment is available. Generally, it is widely said that this type of learning method is not appropriated to obtain dynamic motions because Markov property is not necessarily guaranteed during the dynamic task. However, in this study, we try to avoid this problem by embedding the dynamic information in the robotic state space; the applicability of the proposed method is considered using both the real robot and dynamic simulator. This paper, in particular, discusses how the robot with 5-DOF, in which the Q-Learning algorithm is implemented, acquires a giant-swing motion. Further, we describe the reward effects on the Q-Learning. Finally, this paper demonstrates that the application of the Q-Learning enable the robot to perform a very attractive giant-swing motion.

This paper discusses human weight perception using a haptic device. The objective of this study is to reveal the characteristics in human force sensations, which are difficult to examine in a real environment. Further, we aim to apply the perceptual mechanisms to multimedia applications as the final target. In this study, we particularly examine the weight discriminative powers for various weight changes. Expanding our previous study, we compare the difference thresholds for the weight addition and removal during a goal-directed lifting. A statistical analysis implies that our weight discriminative power for the weight addition tends to improve in the deceleration process. As for the weight removal, the weight discriminative power declines in the deceleration process due to the inertia effect in the vicinity of the target height. In addition, this study tries to reveal the weight perception when the load force is gradually changed. The result implies that the time variation in the load force holds the tremendous potential to enable us to experience attractive force sensations and haptic illusions.

Human beings usually locate their hand at the position with a higher moving potential in order to easily deal with various situations. Inspired by the human hand-arm movement, this study proposes a motion control issue for a serial-linkage finger-arm robot according to Wf.

The main purpose of this study is to apply the mechanism of human weight perception to multimedia applications. When a start and the goal points are given in the human motion, the velocity profile has a unimodal profile including the acceleration and deceleration zones. In such case, it is widely said that the motion control becomes more accurate in the deceleration zone for the final approach. Hence, it is assumed that the sensing ability also improves. This study challenges to confirm the hypothesis with weight stimuli generated by a force display device. As a preliminary experiment, this study confirms that our device enables the evaluation of human perception by tracing Weber's experiment in virtual reality; the obtained difference threshold (DL: Differenz Limen) almost agrees with the previous results. The difference threshold is a very important factor, which means perceptual threshold for weight changes. We further attempt to clarify the mechanism of the human weight perception for sudden weight changes during the lifting process. Based on individual lifting profiles, this study suddenly changes the load force in the two zones, and examines the difference thresholds of each subject. The results demonstrate that the human weight perception tends to become more sensitive in the deceleration zone during the lifting process. These results also imply the effectiveness of force display devices for physical experiments.

The advancement of multimedia services including audio/visual media has been rapid. The applications of cellular phones, in particular, have increased by using these technologies. In addition, if force telecommunication were realized, force information would become a next leading factor in the multimedia service. In this field, a robotic master/slave system is a leading candidate. This system has been studied as a teleoperation system between an operator and an environment; the operator controls only the master device whereas the slave device is never controlled. For multimedia applications, such systems require flexibility and bidirectionality because force telecommunication must consider the interactions between users. This paper details the fundamental issues of force communication from a viewpoint of human perception. With regard to the control system, this study uses an integrated hybrid control master/slave system that helps to find a key factor of equal bilateral force telecommunication in the sensory aspect. The employed system has a function to change the proportion of force display to position display by varying a weight parameter. We discuss the basic control performance of a force telecommunication system and evaluate qualitative feelings of users by using a psychological evaluation method

This paper investigates the motion forms of robots generated by the Q-Learning algorithm during the learning process. We analyzed the manner in which a caterpillar robot, which performs looping motions using two actuators, acquires advance actions by focusing on the process. By observing a series of processes, we confirmed that various motion forms appeared or disappeared as a result of their interactions with the learning process and approach an optimum motion form. In most algorithms, such motion forms cannot appear in the learning process because its framework is almost predetermined by the teacher data, and the cost functions for learning cannot be usually considered as a continuous process. The characteristics of reinforcement learning are very interesting from the viewpoint of biological evolution. This paper describes the effects of the interaction between the robot kinematics and the environment as a direct result of changing the environment. In addition, this study challenged the acquisition of two-dimensional motions with a starfish robot having four actuators. The result demonstrates that the robot can obtain a reasonable motion from the complicated relationships with the environment by skillfully employing its structure. Moreover, this paper implies that the reward manipulation may give a new insight for the learning process by the investigations performed in this study. This paper examines the possibility of the reward combinations for generating arbitrary motions.

Human beings cannot control a position of sphere on the disk without seeing it. Because under such a condition, as we determine the position and estimate the motion of sphere by use of visual information, it is very difficult for human beings to control it using only tactile or force information of a hand. This is why the tactile and the force information are less quantitative for human beings than the visual information. On the other hand, a robot can deal with this qualitative information as quantitative values. Therefore, the robot seems to have the possibility that it carries out such difficult tasks for human beings using only force information. In this paper, we propose the estimation method of the position of sphere (made of crystal) on the disk from the force information measured with three-directional force sensors. Then, we tried to examine whether the robot fingers can control the motion of sphere on the disk using only these force information. Actually, the position and the velocity information estimated from force information enable the robot fingers to control the sphere by applying a simple PD control algorithm. Moreover, this paper adds Lyanpunov’s stability analysis of the proposed control algorithm. Finally, this results show new robot task which human beings cannot realize, whose demonstration is very interesting.

In this paper, by focusing on weight perception, we attempted to clarify a perceptual mechanism using functions of the haptic interface. We especially examined the weight perceptual mechanism when the weight of an object suddenly changed, which does not take place in our natural life. This experimental condition can only be realized by using the advantage of the haptic interface. The results show the difference in the perceptual threshold due to addition and reduction of the weight. Moreover, the results indicate that subjects can also correct the supporting force corresponding to the sudden change in the weight when they could not sense the change. Namely, it implies that subjects adjust the supporting force under an imperceptible state, which may indicate an interesting muscular motion under a state of unconsciousness.

Recently, the haptic interface system (one of a variety of force display devices) has attracted great interest as a new virtual reality technology, stimulating vigorous research. Most reports deal with methods of constructing a haptic interface system or the development of new devices having with a particular mechanism, and the various methods suitable for force display. However, it is also necessary to clarify the relationship between the virtual dynamics characteristics of a system and a human being's feelings in order to present the accurate force sensation from virtual environment. In this paper, we evaluate the force sensations experienced by human beings with the psychological experiments that examine perceptual illusion phenomena, including the horizontal-vertical illusion and the size-weight illusion. These results show that perceptual illusions occurring in a real environment can be also reappeared in a virtual environment. Therefore, perceptual illusions may have the potential for application to virtual reality. Moreover, the characteristics of perceptual illusions can be examined by changing the virtual dynamics parameters of the haptic interface. Finally, this paper shows that the haptic interface is a very effective tool for the investigation of perceptual illusions.