Hardness Perceived When Sliding Over Roughened Surfaces.

The objective of this study was to investigate the influence of roughened surface features on the perceived hardness of various materials. Thirteen participants used a visual analog scale to evaluate the hardness of ten 3D-printed specimens by sliding a fingertip on them. The specimens had two types of surface features: flat and smooth, or with microscopic rectangular gratings. They were fabricated from two types of plastic with different Young's moduli-2.46 and 9.35 MPa. We found that both surface pattern and mechanical hardness significantly contributed to the perceived hardness of a material individually and without interaction. The roughened surfaces with rectangular gratings were judged to be harder than the flat and smooth surfaces of the same material. Among the parameters of the rectangular gratings, the groove width or periodic surface wavelength significantly contributed to the perceived hardness. Although the root cause of this phenomenon is unknown, friction caused by surface roughness is considered a potential mediator that influences the perceived hardness. The findings of this study can facilitate the manipulation of softness perception through surface design.

Surface shape alters perceived material softness.

When a human strokes the surface of an object with his/her finger, the surface shape influences the perceived softness of the object. This study introduced a curved surface softness illusion, which alters the perception of material softness. When a surface with curvature is felt by sliding a finger over it, it feels softer than a flat surface made of the same material. In contrast, a rugged surface is perceived as harder. This illusion indicates that, in addition to mechanical hardness, humans judge an object's softness based on its surface shape.

Effectiveness of palpation technique training and practice using a muscle-nodule-palpation simulator.

[Purpose] Extant techniques for palpating nodules, a diagnostic criterion of myofascial trigger points, lack high reliability. Therefore, this study aimed to investigate the effects of training and practice using a novel muscle-nodule-palpation simulator. [Participants and Methods] Sixteen university students (age range: 19-22 years) were randomly assigned to the training (n=8) and control (n=8) groups and used the muscle-nodule-palpation simulator to determine the position and orientation of the muscle nodule embedded in the model. During the experiment, only the participants in the training group were allowed to practice nodule detection while viewing the model through its transparent material. Subsequently, both groups underwent a performance evaluation. [Results] The training group exhibited greater improvement in performance than the control group. The means and standard errors of the improvement in the proportion of successful localization of the muscle nodule were 0.14 ± 0.06 for the control group and 0.42 ± 0.09 for the training group. [Conclusion] Training using the muscle-nodule-palpation simulator improved palpation technique for nodule localization.

Effect of forward moment on recovery motion against tripping.

Investigating the fall recovery motion mechanism is crucial to prevent fall injuries. Among the various parameters of motion and posture, the forward moment can be considered the representative parameter of the magnitude of tripping from a kinematic perspective. The effect of increasing the forward moment on the recovery motion after tripping was investigated in this study. A tripping experiment was performed on a treadmill, and the recovery motion was observed. The forward moment was artificially increased using several approaches, such as pulling the torso, increasing gait speed, and increasing body mass. Factor analysis was performed to establish the relationship between the recovery motion parameters and forward moment. The distribution of the factor scores implied the uniqueness of the recovery motion of the pull condition. Although the forward moment temporarily increased, it was compensated quickly. The other conditions and factors indicated qualitative similarity of the recovery motion among the different conditions. This study demonstrates that the recovery motion after tripping is robust against an increase in forward moment, regardless of the method used to increase the forward moment. The investigation of reaction motion pattern enables validation of the recovery motion and falling posture estimation. Such fall simulations will facilitate the development of a method of fall prevention and mitigation.

Bumps and Dents are Not Perceptually Opposite When Exploring With Lateral Force Cues.

Virtual tactile bumps and dents are presented by controlling frictional forces on a surface tactile display, a flat touch screen with tactile feedback functions. This technology enables users to touch and feel three-dimensional objects. The resistive force against a sliding finger is increased and then decreased compared to a base level to present a bump. The order of increase and decrease is inverted for a dent. Thus, the difference between bump and dent presentations lies in the change order of the resistive force. However, bumps and dents are not simply opposite when investigating psychophysical functions with only lateral force cues available, without height and depth information. The results demonstrate that bumps are more easily detected with high surface gradients or resultant force changes and small widths. In contrast, these parameters do not influence the detection of dents among different participants. These findings contribute to a deeper understanding of tactile perception of surface shapes.

Skin quality sensor to evaluate vibration and friction generated when sliding over skins.

OBJECTIVE: The mechanical condition and tactile evaluation of skin are essential for the development of skin care products. Most of the existing commercial instruments and studies aim to evaluate the skin surface by pressing it for hardness or by using imaging sensors, but there have been few instrumental measurements employing rubbing motion. Here, we have developed a sensor specialized for tactile sensation and the contact phenomenon during skin rubbing. METHODS: The developed sensor has three features: It can measure body parts including cheeks and arms, automate the rubbing motion of the probe and measure vibration and friction simultaneously. It is hand-held, with metal probes that rub the skin surface while rotating under a motor drive; it has an accelerometer and a force sensor beneath the probe measuring vibration and friction forces. To evaluate the validity of the sensor's measurements, artificial skin models were measured using the developed sensor and commercially available sensors and the results were compared. The relationship between the sensor output, surface roughness measurement and sensory evaluation was also investigated. Additionally, we evaluated the inter-rater reliability when measuring actual skin. RESULTS: The measurements of five artificial skin models with different surface shapes showed a high correlation (r = 0.99) between the vibration intensity values evaluated by the developed sensor and those measured by a tri-axial acceleration sensor attached to a fingernail. The correlation coefficient between the vibration intensity values and surface roughness was r = 0.91, and the correlation with the sensory evaluation score of roughness was r = 0.99. The friction coefficients measured by the developed sensor and the force plate had r = 0.93, based on measurements of five artificial skin models with different friction conditions. The inter-rater correlation coefficients between the three participants of the developed sensor were as high as 0.92 and 0.94 for the vibration and friction measurements respectively. CONCLUSION: The vibration intensities and friction coefficients from the sensor were highly correlated with those of the conventional sensor. The inter-rater reliability was also high. The developed sensor can be useful for tactile evaluation in skin-care product development.

OBJECTIF: l'état mécanique et l'évaluation tactile de la peau sont essentiels au développement de produits de soins de la peau. La plupart des instruments disponibles sur le marché et des études publiées à ce jour évaluent la surface de la peau en la comprimant pour déterminer sa dureté ou en utilisant des capteurs d'imagerie, mais il n'y a eu que peu de mesures instrumentales utilisant le mouvement de frottement. Ici, nous avons développé un capteur spécialisé pour la sensation tactile et le phénomène de contact lors du frottement de la peau. MÉTHODES: le capteur développé possède trois caractéristiques : il permet d'exercer des mesures sur plusieurs parties du corps, y compris les joues et les bras ; il automatise le mouvement de frottement de la sonde et il mesure simultanément les vibrations et les frottements. Tenu à la main, doté de sondes en métal qui frottent la surface de la peau tout en tournant sous l'action d'un moteur, il est équipé d'un accéléromètre et d'un capteur de force situé sous la sonde qui mesure les forces de vibration et de frottement. Pour déterminer la validité des mesures du capteur, des modèles de peau artificielles ont été évalués à l'aide du capteur développé et de capteurs déjà disponibles sur le marché, et les résultats ont été comparés. Le lien entre les mesures réalisées à l'aide du capteur, la mesure de la rugosité de la surface de la peau et l'évaluation sensorielle a également été étudié. En outre, nous avons évalué la fiabilité inter-évaluateurs lors de la mesure réelle de la peau. RÉSULTATS: les mesures de cinq modèles de peau artificielle avec des formes de surface différentes ont montré une forte corrélation (r = 0,99) entre les valeurs d'intensité des vibrations évaluées par le capteur développé et celles mesurées par un capteur d'accélération triaxial fixé à un ongle. Le coefficient de corrélation entre les valeurs d'intensité des vibrations et la rugosité de la surface était r = 0,91, et la corrélation avec le score d'évaluation sensorielle de la rugosité était r = 0,99. Les coefficients de frottement mesurés par le capteur développé et la plaque de force étaient r = 0,93, sur la base des mesures de cinq modèles de peau artificielle avec des conditions de frottement différentes. Les coefficients de corrélation inter-évaluateurs entre les trois participants utilisant le capteur développé ont atteint 0,92 et 0,94 pour les mesures de vibrations et de frottement, respectivement. CONCLUSION: les intensités des vibrations et les coefficients de frottement du capteur se sont avérés fortement corrélés avec ceux du capteur conventionnel. La fiabilité inter-évaluateurs était également élevée. Le capteur développé peut être utile pour l'évaluation tactile lors du développement de produits de soins de la peau.

Relationship between gait stability indices and gait parameters comprising joint angles based on walking data from 288 people.

Stability during walking is essential because falling accidents may lead to severe injuries. In this study, we calculated the margin of stability (MoS) and the maximum Lyapunov exponent (λs), which are two major stability indices for walking, using a gait database representing 300 healthy people. Previously, the relationships between these indices and other gait parameters, including joint angles, have not been investigated in such a large subject pool. Therefore, we determined the relationships between these stability indices and the gait parameters by calculating correlation coefficients and performing multiple regression analysis. The results indicated that MoS is dominated by walking speed in the forward direction and associated with various joint angles in the lateral direction. Conversely, no relationships were identified between λs and the gait parameters. Although both MoS and λs are considered as measures of gait stability, they are independent. The results of this study suggest that MoS and λs represent different aspects of gait motion.

TDS Similarity: Outlier Analysis Using a Similarity Index to Compare Time-Series Responses of Temporal Dominance of Sensations Tasks.

Temporal dominance of sensations (TDS) methods are used to record temporally developing sensations while eating food samples. Results of TDS tasks are typically discussed using averages across multiple trials and panels, and few methods have been developed to analyze differences between individual trials. We defined a similarity index between two time-series responses of TDS tasks. This index adopts a dynamic level to determine the importance of the timing of attribute selection. With a small dynamic level, the index focuses on the duration for attributes to be selected rather than on the timing of the attribute selection. With a large dynamic level, the index focuses on the temporal similarity between two TDS tasks. We performed an outlier analysis based on the developed similarity index using the results of TDS tasks performed in an earlier study. Certain samples were categorized as outliers irrespective of the dynamic level, whereas the categorization of a few samples depended on the level. The similarity index developed in this study achieved individual analyses of TDS tasks, including outlier detection, and adds new analysis techniques to TDS methods.

Short-term repeated sprint training in hypoxia improves explosive power production capacity and repeated sprint ability in Japanese international-level male fencers: A case study.

This case study reports the effects of six sessions of repeated sprint training in hypoxia (RSH) over 3 weeks on explosive power production capacity and repeated sprint ability (RSA) in two Japanese international-level foil fencers. The six RSH sessions (60-s sprints in total per session: consisting of two sets of five 6-s sprints with 30-s passive recovery, at simulated altitude of 3000 m) caused improvements of peak power output (PPO; Athlete A: 5.1%; Athlete B: 3.2%) and mean power output (MPO; Athlete A: 4.4%; Athlete B: 1.6%) over the 10 repeated sprints, respectively. The observed findings suggest that as few as six RSH sessions over 3 weeks can improve, at least to some extent, explosive power production capacity (PPO) and RSA (MPO) in the two elite fencers. To the best of our knowledge, this is the first study to apply short-term RSH in combat sport (fencing) with international-level athletes. Further studies are required to explore the effectiveness of short-term RSH in combat sports with a more robust study design (e.g., randomized control trial with adequate statistical power) as the modality of RSH would suit physical and physiological demands in the majority of combat sports (e.g., wrestling, boxing).

Young's moduli of subcutaneous tissues and muscles under different loads at the gluteal region calculated using ultrasonography.

[Purpose] Young's modulus distributions for subcutaneous and muscle tissues in a large sample of healthy individuals, based on ultrasonography and compression testing, remains uninvestigated till date. This study aimed to separately estimate the hardness of subcutaneous tissues and muscles in the human gluteal region under a range of loads in terms of mean Young's moduli and associated distributions. [Participants and Methods] Data of 21 males aged 20-22 years were acquired using synchronous compression testing and ultrasonography. Stress-strain curves comprised the loads applied (stress) were plotted against ultrasonographic changes in subcutaneous/muscle tissue thickness (strain). Young's moduli were calculated as slopes of approximation curves fitted to highly linear regions of the stress-strain curves. [Results] Young's moduli (mean ± standard deviation) for gluteal subcutaneous and muscle tissues were estimated as: 26.1 ± 19.0 kPa, 1-N load; 2,199.1 ± 1,354.8 kPa, 30-N load; and 62.2 ± 10.3 kPa, 5-N load; 440.4 ± 80.0 kPa, 30-N load, respectively. No correlation between any pair of these measures reached statistical significance. [Conclusion] Young's moduli were successfully measured for subcutaneous and muscle tissues in a large participant sample using ultrasonography and compression testing. Our results may serve as reference data when assessing tissue hardness by palpation.

Multiple Spatial Spectral Components of Static Skin Deformation for Predicting Macroscopic Roughness Perception.

A previous study suggested a relationship between the spatial spectrum of finger pad skin deformation and perception of macroscopic roughness features. This study tested a new hypothesis that macroscopic roughness perception is the result of a weighted linear combination of multiple spatial spectral components of skin deformation. Experiments were conducted by capturing close-up images of finger pad deformation while the pads were pushed onto specimens with macroscopic features. Additionally, the roughness perceptions of these specimens were collected using a magnitude estimation method. The combination of spectral components predicted the roughness perception more accurately than any single spectral component. This suggests that roughness perception is mediated by multiple Gabor filter-like neural systems with different spatial periods, such as visual perception.

Linking Temporal Dominance of Sensations for Primary-Sensory and Multi-Sensory Attributes Using Canonical Correlation Analysis.

Sensory responses dynamically change while eating foods. Temporal dominance of sensations (TDS) methods record temporal evolution and have attracted attention in the last decade. ISO 13299 recommends that different levels of attributes are investigated in separate TDS trials. However, only a few studies have attempted to link the dynamics of two different levels of sensory attributes. We propose a method to link the concurrent values of dominance proportions for primary- and multi-sensory attributes using canonical correlation analysis. First, panels categorized several attributes into primary- and multi-sensory attributes. Primary-sensory attributes included sweet, sour, fruity, green, watery, juicy, aromatic, and light. Multi-sensory attributes included refreshing, fresh, pleasurable, rich/deep, ripe, and mild. We applied the TDS methods to strawberries using these two categories of attributes. The obtained canonical correlation model reasonably represented the relationship between the sensations in a reductive manner using five latent variables. The latent variables couple multiple primary- and multi-sensory responses that covary. Hence, the latent variables suggest key components to comprehend food intake experiences. We further compared the model based on the dominance proportions and the time-derivatives of the dominance proportions. We found that the former model was better in terms of the ease of interpreting the canonical variables and the degree to which the canonical variables explain the dominance proportions. Thus, these models help understand and leverage the sensory values of food products.

Surfaces With Finger-Sized Concave Feel Softer.

The judgment of elastic softness is determined not only by mechanical parameters related to hardness, such as the elastic modulus and stiffness, but also by macroscopic surface features. This study experimentally demonstrates that objects with a finger-sized concave with a depth of 1-3 mm feel softer than flat surfaces made of the same materials when they are pushed by a finger. In Experiment 1, participants judged the surfaces of a rigid material with thumb-sized concaves to be softer than the flat and convex surfaces. Experiment 2 used rubbers of various elastic moduli, and the softness of a concave object with a Young's modulus of 0.55 MPa was subjectively equal to that of a flat object with an average Young's modulus of 0.23 MPa. Furthermore, the softness of a convex object was subjectively equal to that of a 1.68 MPa flat object. The contact phenomena between a finger pad and concave or convex objects are different from those between a finger pad and flat objects, and they influence the softness judgment. Such phenomena include the relationship between the pressing force and contact area. These results provide insights into surface design and improve comprehension of the perceptual principles of softness.

Tactile Texture Rendering for Electrostatic Friction Displays: Incorporation of Low-Frequency Friction Model and High-Frequency Textural Model.

Tactile texture presentation on touch panels enhances their usability and realizes immersive user interfaces. This study develops a tactile texture rendering method for electrostatic friction displays. The method combines two rendering models for material textures compared with previous studies which focused on either of these two models. One of these models is a physical model that simulates low-frequency frictional signals depending on the exploratory finger velocities and contact loads. The other is an autoregression-based data-driven model for high-frequency textural friction. For user studies, we compared combining the two models with using only the physical model for the four types of materials. Although the effectiveness varied across the materials, the subjectively judged realism and identification of the materials were improved for the combined condition. The new method combining high-frequency textural information and low-frequency physical model-based friction is expected to provide realistic tactile textures for electrostatic surface tactile displays.

Bootstrap Resampling of Temporal Dominance of Sensations Curves to Compute Uncertainties.

In the last decade, temporal dominance of sensations (TDS) methods have proven to be potent approaches in the field of food sciences. Accordingly, thus far, methods for analyzing TDS curves, which are the major outputs of TDS methods, have been developed. This study proposes a method of bootstrap resampling for TDS tasks. The proposed method enables the production of random TDS curves to estimate the uncertainties, that is, the 95% confidence interval and standard error of the curves. Based on Monte Carlo simulation studies, the estimated uncertainties are considered valid and match those estimated by approximated normal distributions with the number of independent TDS tasks or samples being 50-100 or greater. The proposed resampling method enables researchers to apply statistical analyses and machine-learning approaches that require a large sample size of TDS curves.

Properties of muscle nodules recognized by manual physical therapy practitioners.

[Purpose] The purpose of this study was to describe the properties of muscle nodules (kinkoketsu) recognized by manual physical therapy practitioners. [Participants and Methods] A total of one hundred and thirty-three physical therapists, occupational therapists, judo therapists, and acupuncturists participated in this study. The shape, size, direction, depth, and hardness of muscle nodules, often treated in the buttocks, were investigated through the completion of a questionnaire. [Results] A total of 124 answer sheets were completed; 112 of these described the shape of muscle nodules as ellipsoidal. Of these 112 sheets, 97 effective sheets were analyzed. The results showed that the mean long axis length, short axis length, and thickness of the muscle nodules were 30.9 mm, 16.2 mm, and 9.3 mm, respectively. The most common responses on the long axis direction, depth, and hardness of the muscle nodules were the craniocaudal orientation, the second shallowest layer of 5 divisions, and the eraser level, respectively. [Conclusion] The typical muscle nodule found in the buttocks by manual physical therapy practitioners is roughly the shape of a large almond.

Machine-assisted foot stretching in the elderly: a comparison with self-stretching.

[Purpose] Self-stretching is the traditional at-home stretching method of choice. We developed an automatic foot-stretching machine to perform effective dorsiflexion stretching safely and easily at home. The effects of automatic stretching using our machine and self-stretching were investigated and compared. [Participants and Methods] Twelve healthy elderly people participated in the study. Automatic dorsiflexion static stretching was performed with the right foot, and self-stretching using a towel was performed with the left foot. Before and after each stretching, passive range of motion in dorsiflexion, maximal voluntary contraction strength in plantarflexion, passive resistive torque during passive dorsiflexion, and displacement of the muscle-tendon junction of the medial gastrocnemius muscle were measured. [Results] The range of motion in dorsiflexion had a significantly greater increase after automatic stretching than after self-stretching. The maximum strength in plantarflexion tended to decrease after automatic stretching but did not decrease after self-stretching. The passive resistive torque in both types of stretches decreased in some of the participants but increased in others. The displacement of the muscle-tendon junction of the medial gastrocnemius tended to shorten during automatic stretching as compared with self-stretching. [Conclusion] Foot stretching using a machine is as effective as self-stretching and tends to affect the tendon rather than the muscle.

HumTouch: Localization of Touch on Semi-Conductive Surfaces by Sensing Human Body Antenna Signal.

HumTouch is a touch sensing technology utilizing the environmental electromagnetic wave. The method can be realized using conductive and semi-conductive materials by simply attaching electrodes to the object's surface. In this study, we compared three methods for localizing a touch on 20×16cm2 and 40×36cm2 papers, on which four or eight electrodes were attached to record the voltages leaked from the human fingertip. The number and positions of the electrodes and the data processing of the voltages differed according to the localization methods. By constructing a kernel regression analysis model between the electrode outputs and the actual physical locations, the touched locations were estimated. Each of the three methods was tested via leave-one-out cross validation. Out of the three methods discussed, two exhibited superior performances in terms of the estimation errors. Of these two methods, one simply uses the voltages recorded by the four electrodes attached on the middle of paper edges as inputs to the regression system. The other uses differential outputs of electrode pairs as the inputs. The smallest mean location errors were 0.31 cm on 20×16cm2 paper and 0.27 cm on 40×36cm2 paper, which are smaller than the size of a fingertip.

Principal motion analysis of manual stretching techniques for the ankle joints.

[Purpose] Physical therapists frequently perform manual stretching of the ankle joints. Manual stretching procedures are challenging to define because they involve multidirectional joint motions and external forces. Therefore, in this paper, we propose a method for quantitatively and statistically analyzing the manual foot stretching techniques used by physical therapists. [Participants and Methods] The participants were four physical therapists, and three patients who have a spastic foot. We investigated the manual foot stretching techniques employed by the physical therapists using a three-dimensional analysis system and an instrumented brace with force sensors. Principal motion analysis was applied to the obtained data, and principal motions were determined. [Results] The first principal motion was the application of force for the dorsiflexion of the foot; second, the pushing/pulling of the heel; third, the eversion/inversion of the entire foot; and fourth, the eversion/inversion of the forefoot. Furthermore, the manual stretching techniques varied among the physical therapists, even for the same patient, and some techniques occurred only between particular pairs. [Conclusion] This study demonstrated the effectiveness of the principal motion analysis for the statistical assessment of manual stretching techniques and clarifying differences in stretching technique among physical therapists.

Safety considerations for forward falls.

OBJECTIVE: Forward falls are among the most frequent causes of upper extremity fractures. This study investigated the safety considerations to prevent wrist injuries during bimanual forward falls. METHODS: A biomechanical model was developed with two separated arms to facilitate investigation of asymmetrical contact and predict the impact force applied to each hand separately. To validate the developed model, a series of fall experiments were conducted in which one hand collided with a hard surface, while the other collided with a soft surface. RESULTS: The results show that the impact force applied to each hand is independent of the other. Using these results and our model, the safety aspects of human forward falls were analyzed with a view to preventing injuries. Specifically, we sought to determine the safe range of surface stiffness and damping to ensure that the occurrence of forward falls does not lead to trauma. CONCLUSION: The results of this study can be applied in the design of compliant flooring to ensure the safety of people in environments with potential fall hazards. From a robotics viewpoint, the results are applicable in the design of compliant flooring for shared workplaces, where robots collaborate with people and collisions between humans and robots may cause falls.