This paper describes the perceptual characteristics of a sense of a force induced by asymmetric vibration using a vibration speaker-type non-grounded haptic interface. We confirm that the vibration speaker generates a perceived force that pulls or pushes a user's hand in a particular direction when an asymmetric amplitude signal that is generated by inverting a part of a sine wave is input. In this paper, to verify the system with respect to various factors of force perception caused by asymmetric vibration, we conducted six experiments and the following results were obtained. (1) The force vector can be controlled by reversing the asymmetric waves. (2) By investigating the physical characteristics of the vibration, asymmetric vibration was confirmed. (3) The presentation of vibration in the shear direction on the finger pad is effective. (4) The point of subjective equality of the perceived force can be controlled by up to 0.43 N by changing the amplitude voltage of the input signals. (5) The minimum stimulation time required for force perception is 66.7 ms. (6) When the vibration is continuously presented for 40 to 50 s, the perceived force decreases because of adaptation. Hence, we confirmed that we can control both the direction and magnitude of the reaction force by changing the input signal of the vibration speaker.

When presented with asymmetric vibrations, humans experience an illusory force, similar to the sensation of being pulled in a particular direction. A pulling illusion has also been used in new display elements for a VR content and a pedestrian navigation system. However, the basic design of asymmetric vibration stimuli that can induce this illusion has not yet been determined. In particular, it is unclear as to which part of the vibration waveform should be asymmetric to induce an illusion. To better understand the design of asymmetric vibration stimuli that can induce a pulling illusion, we evaluated the effect of the illusion corresponding to the waveform deformation due to a change in phase difference of asymmetric-vibration frequency components. The results of a psychophysical experiment demonstrate that when the phase differences of the fundamental and second harmonic waves of the asymmetric vibration are close to 0 deg or -180 deg, the illusion is more likely to occur. This result implies that the difference in the rate by which the acceleration changes at each polarity contributes to the illusion.

A white cane is conventionally used by visually impaired persons to assist their mobility. To learn its proper operation, training by an orientation & mobility specialist is necessary. However, because the number of specialists is limited, visually impaired persons often do not receive sufficient training. To rectify this issue, a training environment in which the visually impaired can train independently is required. This paper proposes a training system that enables the visually impaired to learn white cane techniques using illusory pulling cues. Specifically, in the white cane touch technique, which is a basic white cane technique, a system that targets the swing width of the white cane is presented by illusory pulling cues. To verify the efficacy of the system, a prototype was implemented and evaluated via user tests. The results confirmed that the error of the swing width of the white cane decreased following use of the proposed system. The proposed system will contribute to the development of the mobility of the visually impaired by enabling them to train with the white cane independently and spontaneously, thereby reducing the workload of specialists.

It is known that humans experience a haptic illusion, such as the sensation of being pulled in a particular direction, when asymmetric vibrations are presented. A pulling illusion has been used to provide a force feedback for a virtual reality (VR) system and a pedestrian navigation system, and the asymmetric vibrations can be implemented in any small non-grounded device. However, the design methodology of asymmetric vibration stimuli to induce the pulling illusion has not been fully demonstrated. Although the frequency of the asymmetric vibration is important, findings on the frequency have not been reported. In this study, we clarified the influences of the effects on the pulling illusion based on the investigation of asymmetric vibration frequency differences. Two psychophysical experiments that related to the frequency of asymmetric vibration were performed. Experiment I showed that the illusion occurs for specific vibration waveforms at 40 Hz and 75 Hz. As a result of Experiment II, the threshold was the lowest when the frequency was 40 Hz, and highest when the frequency was 110 Hz. This result supports the previous hypothesis that the Meissner corpuscles and the Ruffini endings contribute to the illusion, while the Pacinian corpuscles do not.

It is known that humans experience a kinesthetic illusion similar to a pulling sensation in a particular direction, when subjected to asymmetric vibrations. In our previous study, we developed a device that can apply a translational force and a torque to induce this illusion. The illusory translational force might induce a reaching motion of the upper limb, and the applied torque might induce a flexion–extension motion of the wrist. In the present study, we experimentally verified whether these motions can be induced. The results confirmed that the device could guide the upper limb with a success rate of 94.3% when switching between the application of the translational force and the torque. The results suggested that torque application could be a cue for the user to determine the movement direction intuitively.