Hikaru Nagano

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.

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.

Haptic Invitation of Textures: Perceptually Prominent Properties of Materials Determine Human Touch Motions

In daily life, certain textures and materials invite our touch motions. To seek the nature of such haptic invitation, we conducted a series of experiments consisting of sensory evaluations and ranking tasks for 36 materials to ascertain their perceptual properties and their degrees of haptic invitation. In addition, we recorded the human touch motions elicited by these materials. The results showed high degrees of haptic invitation for materials with perceptually prominent textures, which indicates that such textures frequently invite human touch motions. We also developed a Bayesian network model that represented the probabilistic relationships between invited touch motions and the properties of textures. The model substantiated the observation that different types of textural prominence led to different types of invited touch motions. These results collectively suggest that materials with prominent textures frequently encourage humans to touch them, using appropriate or specified touch motions.

Spectrum-based synthesis of vibrotactile stimuli: active footstep display for crinkle of fragile structures

When a human crinkles or scrunches a fragile object, for which the yield force is very small that it is hardly perceived, they identify the material of the object based on tactile stimuli delivered to the skin. In addition, humans are able to recognize materials even when they are crinkled at different speeds. In order to realize these human recognition features of the crinkle of a fragile object, we develop a vibrotactile synthesis method. This method synthesizes the vibrotactile acceleration stimuli in response to a crinkle speed based on the preliminarily measured acceleration spectra. Using this method, we develop an active footstep display that presents a virtual crinkle of fragile structures made of different materials to its users. Experimental participants could identify three of the four types of virtual structure materials at rates significantly higher than the chance level. The four materials were copy and typing paper, aluminum foil, and polypropylene film. Furthermore, the trends of answer ratios exhibit good correspondence with those for the real cylindrical fragile objects. We conclude that the developed method is valid for the virtual crinkle of fragile structures and will enhance the validity of virtual reality systems, such as a virtual walkthrough system.

Spectrum-based vibrotactile footstep-display for crinkle of fragile structures

This study developed a vibrotactile display method for the crinkle/scrunch of fragile structures. For such structures, tactile stimuli are more easily perceived by humans than the very small reaction forces that occur during a crinkle. The developed method synthesizes vibrotactile acceleration stimuli for a crinkle based on the preliminarily measured acceleration spectra. We developed a footstep display that presents the synthesized stimuli to human soles in response to the humans foot speed. The display presents the sensations acquired by stepping on fragile structures. Experimental participants identified the types of materials of cylindrical fragile structures among paper, aluminum foil, and polypropylene film, at probabilities significantly higher than the chance level.

Hardness perception by tapping: Effect of dynamic stiffness of objects

Humans can judge the hardness of an object by tapping its surface using a fingertip. The damped natural vibration caused by tapping is a vibrotactile cue for hardness perception. We investigated how dynamic characteristics of an object or vibration influence the hardness perceived by tapping. Using multivariate analyses, the subjectively reported hardness was linked with the dynamic stiffness of an object. Dynamic stiffness, which characterizes the impulsive response of an object, was acquired across 40–1,000 Hz for fourteen types of material cuboid through a hammering test. These blocks were also ranked by seven participants based on their hardness perceived when the participants tapped them with a finger. It was found that the dynamic stiffness did not equally affect the hardness perception across the wide frequency range. Its sensitivity displayed a peak around 200–400 Hz and decreased or disappeared at greater frequency bands in which human perceptual capability is limited.

Haptic invitation of textures: an estimation of human touch motions

Some textures invite human touch motions in daily life, but studies on the methodology of designing such textures have just been initiated [1,2,3]. However, there is still no method of identifying various touch motions invited by these textures. For example, some textures are likely to invite stroking, while others are likely to invite pushing. We developed a Bayesian network model that represents the probabilistic relationships between texture-invited touch motions and properties of textures. We interpreted the constructed model and confirmed that the model is potentially useful for the estimation of human motions.

What appeals to human touch? Effects of tactual factors and predictability of textures on affinity to textures

For reasons that have not yet been investigated, some textures appeal to human touch. We investigate the relationships between the physical and sensory factors, the predictability of textures, and their appeal to human touch. We conduct sensory evaluation of 24 artificial clay textures, and the results are analyzed using factor analysis. Experimental results identify five sensory factors. We reveal that 70–80% of the textures appeal to human touch can be described on the basis of the sensory and physical factors. We propose two models involving the predictability of textures. These models, as well as models based on the sensory and physical factors, explain the affinity to textures.

Physical and sensory factors of textures that appeal to human touch

Some textures appeal to human touch, the reasons for which have not been investigated. We investigate the relationship between the physical and sensory factors of 24 clay textures. Experimental results reveal that 70%–80% of the textures appeal to human touch can be explained on the basis of these factors.

Semantically Layered Structure of Tactile Textures

This study constructed a multi-layered semantic structure of adjective pairs that are used to express the tactile properties of materials. We analyzed the causalities between adjectives using the DEMATEL method, involving twenty-nine adjective pairs and forty-six materials, and thus constructed a multi-layered structure. The constructed structure contained psychophysical, affective, and preferential layers. The psychophysical layer consisted of words related to the physical properties of materials, which were rough/smooth, uneven/flat, hard/soft, cold/warm, sticky/slippery, and wet/dry. The affective layer included affective sensations such as comfortable/uncomfortable and friendly/unfriendly. The words related to individual preferences, which include rich/poor, good/bad, like/dislike, and happy/sad, were located on the highest layer of the structure. The constructed structure helps us understand affective and preferential perceptions of materials through psychophysical perceptions.