Shogo Okamoto

Psychophysical Dimensions of Tactile Perception of Textures

This paper reviews studies on the tactile dimensionality of physical properties of materials in order to determine a common structure for these dimensions. Based on the commonality found in a number of studies and known mechanisms for the perception of physical properties of textures, we conclude that tactile textures are composed of three prominent psychophysical dimensions that are perceived as roughness/smoothness, hardness/softness, and coldness/warmness. The roughness dimension may be divided into two dimensions: macro and fine roughness. Furthermore, it is reasonable to consider that a friction dimension that is related to the perception of moistness/dryness and stickiness/slipperiness exists. Thus, the five potential dimensions of tactile perception are macro and fine roughness, warmness/coldness, hardness/softness, and friction (moistness/dryness, stickiness/slipperiness). We also summarize methods such as psychological experiments and mathematical approaches for structuring tactile dimensions and their limitations.

Real-time remote transmission of multiple tactile properties through master-slave robot system

Remote transmission of high quality sense of touch requires the representation of multiple tactile properties and compensation of communication delay. We developed a real-time remote transmission system that can deliver multiple tactile properties using a master-slave robot system. First, we assessed what type of tactile properties should be transmitted and how to connect them in real time. Three tactile properties—roughness, friction, and softness—were transmitted on the basis of the real-time estimated physical properties of three main wavelengths, a kinetic friction coefficient, and spring constants, respectively. Tactile stimulations were generated in synchronization with hand exploration at the master side by using local tactile generation models to compensate for communication time delay. The transmission of multiple tactile properties was achieved by the integration and enhancement of our previously reported methods for vibrotactile displays and tactile sensors. A discrimination experiment using different materials showed the feasibility of the total system involving the three tactile properties.

Detectability and Perceptual Consequences of Delayed Feedback in a Vibrotactile Texture Display

This study estimated the maximum allowable system latency for haptic displays that produce tactile stimuli in response to the hand movements of users. In Experiment 1, two types of detection thresholds were estimated for the time delay of stimuli through psychophysical experiments involving 13 participants. One was a threshold for the users to notice the existence of a time delay. The other was a threshold for the users to experience changes in the perceived textures in comparison with stimuli with no time delay. The estimated thresholds were approximately 60 and 40 ms, respectively. In interviews, the participants reported that they experienced various types of subjective changes due to the time delay. In Experiment 2, the types of subjective sensations that might be altered by the time delay were investigated. The time delays were controlled based on the acceleration of the hand motions of the participants. The participants evaluated the differences in the perceived textures between the stimuli with a controlled time delay and ones with no delay. The results indicated that the participants associated the time-delayed stimuli with changes in mechanical parameters such as kinetic friction coefficient in addition to changes in the perceived roughness of the textures.

Vib-Touch: Virtual Active Touch interface for handheld devices

Haptic interaction with handheld devices is limited by space and size constraints that inhibit free hand exploration. We developed a compact haptic interface called Vib-Touch, which is operated by fingertip via a pointing-stick input device containing a tactile feedback. A cursor on the screen could perform virtual exploration as a substitute for the finger movement. We call this technology Virtual Active Touch. We also propose a tactile stimulation method to represent not only tactile sensations, but the whole touch experience, including kinesthetic senses and a sense of shapes perceived by a fingertip. This study reports on the first prototype of the Vib-Touch interface for handheld devices. We confirmed that the prototype could provide friction sensation and geometric shape information using the proposed friction display method.

Vibrotactile Stimulation to Increase and Decrease Texture Roughness

We have developed a texture display system that modifies the perceived roughness of textured surfaces via a voice coil actuator worn on the finger. To increase the roughness sensations, the vibrotactile stimuli from the actuator simulate the skin deformations that are activated when a wavy surface is scanned. Conversely, to decrease the roughness sensations of the textured surface, a high-frequency vibrotactile stimulus offsets the activity levels of tactile mechanoreceptors. This offset suppresses the perceived roughness of the surfaces being touched, with increase in the offset correlating with increase in the feeling of smoothness of the surfaces. We conducted an experiment in which we tested the effects of these two types of vibrotactile stimulation on grating roughness specimens, with subjective responses acquired from eight participants via the magnitude estimation method. The results obtained indicate that our method selectively increases and decreases the roughness felt. The intention is for the technique to be used to develop an augmented reality device for textures.

Vibrotactile Stimuli Applied to Finger Pads as Biases for Perceived Inertial and Viscous Loads

The perception of the mass and viscosity of an object is based on the dynamic forces applied to our hands when we jiggle or lift the object [1], [2], [3]. This force is commonly assumed to be sensed by kinetic receptors [4] in our muscles or tendons. When jiggling objects, we also experience the cutaneous deformation of our finger pads. In this study, we show that the dynamic vibration on the finger pad influences our perception of mass and viscosity. We experimentally confirm that the vibration on the finger pad, that synchronizes with the hands accelerations or velocities, enhances the perceived changes in the mass or viscosity when the vibrotactile stimuli and the changes in the mass and viscosity are in the same perceptual direction. For example, when the increased mass and an acceleration-synchronized tactile stimulus-which is a positive bias for the mass-are simultaneously presented to the experiment participants, they respond that the perceived increase in the mass is enhanced. In contrast, when the tactile and proprioceptive stimuli are in perceptually opposite directions, the vibrotactile stimuli cancel the perceived changes in the mass and viscosity. In particular, the effect of the velocity-synchronized vibration on perception is stronger than the effect of the actual viscosity.

Vibrotactile display approach that modifies roughness sensations of real textures

In this study, we developed vibrotactile display methods that can assist designers in product design. In order to achieve realistic sensations required for such designing purposes, we used real materials such as cloth, paper, wood, and leather and applied vibrotactile stimuli to modify the roughness sensations of these materials. This approach allowed us to present textures of various virtual materials with a strong sense of reality. We verified that our proposed methods could selectively modify the fine and macro-roughness sensations of real materials. The methods are expected to aid product designers in deciding tactile sensations suitable for their products.

Validation of Simulated Robots with Realistically Modeled Dimensions and Mass in USARSim

In the case of simulators of mobile robots, it is necessary to clarify the similarity between actual and simulated robots in order to improve the efficiency and transparency of simulators as research tools. Because of its real-time performance, USAR-Sim [1] has been popularly used in studies involving human-robot interactions. However, since USARSim uses approximations and abbreviations in its physical computations, there are some doubts over its computational accuracy. The objective of this study is to compare the actual and simulated robots in order to investigate whether the simulated environments can be used as a training tool. The authors modeled two types of response robots -IRS Soryu [2] and Kenaf [3]- and compared the abilities of the simulated robots and the actual robots in navigating obstacles such as steps and trenches. The dimensions such as heights, widths and lengths and total mass of the real robots were accurately modeled in the simulation and the other physical parameters were assigned default values. It was observed that the maximum error in the sizes of the traversable objects was 18 % of the body length of the robot. It was also found out that the angular velocities of the robots were significantly different for the real and simulated robots. The conclusion is that a training system can be built based on USARSim when the simulated environments involve simple obstacles because there are not significant discrepancies between the basic traversing abilities of the actual robots and those of the simulated robots.

Lossy Data Compression of Vibrotactile Material-Like Textures

Tactile content will be delivered over the Internet in the near future. Vibrotactile material-like textures that resemble the surfaces of wood, leather, etc., are representative of such content. We performed lossy compression of texture data for reducing the data size. We confirmed the effectiveness of two compression strategies: quantization and truncation of data beneath a shifted perceptual threshold curve. In the quantization strategy, the amplitude spectra of vibrotactile textures could be quantized in 14 steps. This reduced the data size to approximately one quarter without any noticeable quality deterioration. The method for truncating frequency components with amplitudes smaller than a shifted perceptual threshold curve was also effective, and it was preferable to the automatic deletion of subthreshold amplitudes. We reduced the data size of vibrotactile material textures to 10-20 percent of their original size by combining the lossy data compression strategy with Huffman coding, which is a lossless data compression method. Lossy compression algorithms will enhance the online delivery of vibrotactile material-like textures by decreasing their data size without significant loss of quality.

Effects of Mechanical Parameters on Hardness Experienced by Damped Natural Vibration Stimulation

Humans can perceive the hardness of an object from the damped natural vibration produced by tapping its surface. This damped natural vibration can be used in hap tic rendering to effectively present a sense of the hardness of an object. Although its frequency is known to influence the subjective hardness, the effects of the viscosity or decay rate have yet to be studied. We researched the contributions of the mass, viscosity, and stiffness to the hardness perception using a commercial force display and psychophysical experiments, where only the vibratory displacement was presented. As a result, the stiffness was found to have a positive effect on the subjective hardness, similar to the usual hap tic rendering of an object. The mass of the object was negatively correlated with the subjective hardness. These results indicated that the vibratory frequency was the dominant parameter in determining the perceived hardness, which agreed with the previous reports on the perceptual effect of damped natural vibration. In contrast, the perceptual effect of the viscosity depended on the individual. For approximately half the participants, the viscosity did not directly influence the subjective hardness of an object. Some participants felt that a damped natural vibration with greater viscosity was harder. However, the other participants felt that it was harder with a smaller viscosity, which suggested that the decay rate of the mechanical system was used as a criterion to judge the hardness of an object. Therefore, the results indicated that the vibratory frequency is a general parameter that can be used to specify the subjective hardness, whereas the perceptual influence of the viscosity or decay rate depends on the individual.