Inter-hemispheric somatosensory coherence and parental stress in hypersensitivity at 8 months old: An electroencephalography study.

OBJECTIVE: Infant hypersensitivity affects daily challenges and parental stress. Although the crucial role of tactile sensation in infants' brain function has been highlighted, hypersensitive infants and their families lack support. Electroencephalography may be useful for understanding hypersensitivity traits. We investigated the relationship between infant perceptual hypersensitivity and parental stress, somatosensory-evoked potential (SEP), and magnitude-squared coherence (MSC) in the general population. METHODS: Infants aged 8 months (n = 63) were evaluated for hypersensitivity and parental stress using a questionnaire and for cortical activity using electroencephalography. Vibration stimuli were applied to the infant's left foot. SEP components that peaked around 150 ms (N2) and at 200 ms (P2) after stimulus onset were evaluated by amplitude and latency at the midline electrode (Cz) and MSC between the midline electrodes (C3-C4). RESULTS: Parental stress was associated with infant hypersensitivity. The latency of Cz was delayed, and C3-C4 delta MSC was high in infants with hypersensitivity. CONCLUSIONS: Increasing inter-hemispheric MSC synchrony in the stimulated condition in infants with hypersensitivity suggested atypical somatosensory cortical function. SIGNIFICANCE: These findings contribute to identifying, understanding the mechanisms of, and developing effective coping strategies for early-stage hypersensitivity.

Influence of Excitation Frequency on the Performance of Peripheral Blood Flow Imaging using Electrical Impedance Tomography.

This paper presents a method for selecting the efficient excitation frequency of Electrical Impedance Tomography (EIT) for imaging peripheral blood flow with high spatial-temporal performance. Using a simulation study, we selected the excitation frequency of 16 kHz to visualize the pulsation of arteries with a high sensitivity. We then conducted a subjective study using 16 electrodes and showed that the conductivity distribution is similar to the anatomical structure of the forearm. Moreover, the integrated conductivity spectrum showed a peak corresponding to a heart rate measurement obtained using a PPG sensor at the fingertip. Therefore, we conclude that this system can capture the spatial-temporal signals related to peripheral artery blood flow by using the selected excitation frequency.

Wearable Skin Resistance-based Tomographic Sensor for Imaging Contact Pressure Distribution on the Human Body.

This study aims to develop a flexible and thin tactile sensor that can capture the contact pressure distribution on the human body. We, therefore, propose a contact resistance-based tomographic tactile sensor that uses the skin as part of the detector. We first evaluated force sensitivity to show that using the skin as a probing layer is possible. We then developed a flexible detector that is 40 mm × 80 mm in size, 200 µm thickness and uses 16 electrodes. As a result, we successfully demonstrated that the proposed method enabled the detection of the contact position within an error of 12.5 % by using frequencies higher than 1 kHz.

Optimization of electrode positions for equalizing local spatial performance of a tomographic tactile sensor.

A tomographic tactile sensor based on the contact resistance of conductors is a high sensitive pressure distribution imaging method and has advantages on the flexibility and scalability of device. While the addition of internal electrodes improves the sensor's spatial resolution, there still remain variations in resolution that depend on the contact position. In this study, we propose an optimization algorithm for electrode positions that improves entire spatial resolution by compensating for local variations in spatial resolution. Simulation results for sensors with 16 or 64 electrodes show that the proposed algorithm improves performance to 0.81 times and 0.93 times in the worst spatial resolution region of the detection area compared to equally spaced grid electrodes. The proposed methods enable tomographic tactile sensors to detect contact pressure distribution more accurately than the conventional methods, providing high-performance tactile sensing for many applications.

Slider Sheet Detection in Charge-Induction Electrostatic Film Actuators.

This work analyzes a built-in slider detection method for a charge-induction type electrostatic film actuator with a high surface-resistance slider. In the detection method, one stator electrode is detached from the parallel driving electrodes and is dedicated to sensing. When a slider with induced charges moves over the sensing electrode, electrostatic induction occurs in the sensing electrode, which causes an electric current. The current is converted to a voltage through a detection resistance, which will be an output of the sensing circuit. This paper provides a framework to analyze the output signal waveform and shows that the waveform consists of two components. One component is caused by driving voltage and appears regardless of the existence of a slider. The other component corresponds to the movement of a slider, which appears only when a slider is moving over the sensing electrode. Therefore, the slider can be detected by monitoring the latter component. The two components generally overlap, which makes the detection of the latter component difficult in some cases. This paper proposes a method to decouple the two components by switching the detection resistance at an appropriate time. These methods are verified using a prototype actuator that has an electrode pitch of 0.6 mm. The actuator was driven with a set of pulse voltages with an amplitude of 1000 V. The experimental results show similar waveforms to the analytical results, verifying the proposed analytical framework. The performance of the sensing method as a proximity sensor was verified in the experiments, and it was confirmed that the slider can be detected when it approaches the sensing electrode within about 3 mm.

Intensity-Adjustable Non-Contact Cold Sensation Presentation Based on the Vortex Effect.

Cold sensations of varying intensities are perceived when human skin is subject to diverse environments. The accurate presentation of temperature changes is important to elicit immersive sensations in applications such as virtual reality. In this article, we developed a method to elicit intensity-adjustable non-contact cold sensations based on the vortex effect. We applied this effect to generate cold air at approximately 0 °C and varied the skin temperature over a wide range. The perception of different temperatures can be elicited by adjusting the volume flow rate of the cold air. Additionally, we introduced a cooling model to relate the changes in skin temperature to various parameters such as the cold air volume flow rate and distance from the cold air outlet to the skin. For validation, we conducted measurement experiments and found that our model can estimate the change in skin temperature with a root mean-square error of 0.16 °C. Furthermore, we evaluated the performance of a prototype in psychophysical cold discrimination experiments based on the discrimination threshold. Thus, cold sensations of varying intensities can be generated by varying the parameters. These cold sensations can be combined with images, sounds, and other stimuli to create an immersive and realistic artificial environment.

Pressure Stimulus to the Palm Substitutes and Augments Force Sensation.

Studies on pseudo-force feedback have reported that tactile stimuli such as skin stretch and pressure can substitute force sensation. This effect has enabled the design of a compact haptic device. However, little is known about the effect of applying pressure to the palm in terms of force substitution and augmentation, especially regarding how active and passive pressure stimuli differ. This article examines the pseudo-force effect of pressure stimuli to the palm, focusing on how it is perceived when it is applied together with a force stimulus. The method of adjustment was utilized, by which participants voluntarily moved their hands to adjust the pressure and force stimuli. The participants did this such that they felt a force equivalent to that of the reference applied to the other hand, which induced only a force stimulus. The results showed that the force sensation was significantly changed by the pressure stimulus to the palm, showing the effect of force substitution and augmentation. Furthermore, we found that there is no significant difference between the active and passive stimuli.

Tomographic Proximity Imaging Using Conductive Sheet for Object Tracking.

This paper proposes a proximity imaging sensor based on a tomographic approach with a low-cost conductive sheet. Particularly, by defining capacitance density, physical proximity information is transformed into electric potential. A novel theoretical model is developed to solve the capacitance density problem using the tomographic approach. Additionally, a prototype is built and tested based on the model, and the system solves an inverse problem for imaging the capacitance density change that indicates the object's proximity change. In the evaluation test, the prototype reaches an error rate of 10.0-15.8% in horizontal localization at different heights. Finally, a hand-tracking demonstration is carried out, where a position difference of 33.8-46.7 mm between the proposed sensor and depth camera is achieved at 30 fps.

Hemodynamic Sensing of 3-D Fingertip Force by Using Nonpulsatile and Pulsatile Signals in the Proximal Part.

This study proposed a novel sensing method of 3-D contact force at a fingertip by using a photoplethysmogram (PPG) device on the proximal part of a finger. The proposed system detects nonpulsatile and pulsatile components of PPG signals from both sides of the proximal part, extracts 16 feature values related to the contact force, and estimates the 3-D force by using a multiple linear regression model. In the validation experiments, the participants wore a PPG device at the proximal parts of their index fingers and applied a contact force at the fingertips for the 11 types of touch actions. The results indicated that satisfactory agreements are observed between the system outputs and the reference forces by the calibrated force sensor. Moreover, the results revealed that the most effective number of feature values corresponded to six for the higher reproducible sensing. Although the development of the effective calibration method is expected to increase robustness, we realized that the proposed method can potentially be used for a 3-D input user interface.

Estimation of Object Elasticity by Capturing Fingernail Images During Haptic Palpation.

In this study, we present a system that performs natural-touch-based elasticity estimation for an object by using a depth camera. To estimate elasticity, which is defined as an object's Young's modulus, a strain-stress curve is obtained from fingernail images during haptic palpation. From a color image, the proposed system detects a fingernail and extracts 10 feature values related to the contact force; then, it estimates the force using a multiple regression model. Deformation of the object was estimated from the finger's three-dimensional position obtained from both color and depth images. Then, a strain-stress curve was determined using the force and deformation data. Evaluation experiments were designed to obtain the strain-stress curves of five objects from 10 participants; then, the estimation performance was investigated. The results show that the reliable range of sensing was within Young's modulus values of 0.12-5.6 MPa and the precision of the measurement was 55 percent of the estimated elasticity.

Hemodynamic sensing of 3D fingertip force using PPG device on proximal part.

This research proposed a novel method to estimate the 3D contact force of a fingertip using a photoplethysmogram (PPG) device on the proximal part of a finger. The proposed method detects non-pulsatile and pulsatile components of PPG signals, extracts eight feature values related to the contact force, and estimates the force by multiple linear regression. In the validation experiments, the participants wore a PPG device at the proximal part of the index finger and applied contact force. Then, the relationship between the contact force and PPG feature values was investigated. As a result, the system was found to be capable of estimating the 3D contact force with a root-mean-square error of 3.5 % of the maximum contact force.

Estimation of Finger Joint Angles Based on Electromechanical Sensing of Wrist Shape.

An approach to finger motion capture that places fewer restrictions on the usage environment and actions of the user is an important research topic in biomechanics and human-computer interaction. We proposed a system that electrically detects finger motion from the associated deformation of the wrist and estimates the finger joint angles using multiple regression models. A wrist-mounted sensing device with 16 electrodes detects deformation of the wrist from changes in electrical contact resistance at the skin. In this study, we experimentally investigated the accuracy of finger joint angle estimation, the adequacy of two multiple regression models, and the resolution of the estimation of total finger joint angles. In experiments, both the finger joint angles and the system output voltage were recorded as subjects performed flexion/extension of the fingers. These data were used for calibration using the least-squares method. The system was found to be capable of estimating the total finger joint angle with a root-mean-square error of 29-34 degrees. A multiple regression model with a second-order polynomial basis function was shown to be suitable for the estimation of all total finger joint angles, but not those of the thumb.

Noninvasive simultaneous measurement of blood pressure and blood flow velocity for hemodynamic analysis.

We describe a noninvasive and simultaneous measurement method of beat-by-beat blood pressure and blood flow velocity waveforms in the radial artery using tonometry and Doppler flowmetry. We conducted a subjective experiment in which hold-down pressure of tonometry was controlled for determining optimal hold-down pressure and the measurement accuracy under the optimal hold-down pressure was evaluated. As a result, blood pressure and blood flow velocity could be measured simultaneously without the influence of the hold-down pressure on the blood flow velocity. It was possible to analyze hemodynamic indicators, such as wave intensity and vascular impedance, with blood pressure and blood flow using the system. The proposed system for detecting unexpected fluctuations in blood pressure and the involved mechanisms may contribute to the treatment of cardiovascular diseases.

Electrotactile Augmentation for Carving Guidance.

In this study, we presented an efficient and unobtrusive tactile feedback system, which is used to train dental technicians in carving tasks using a wax stick and knife. First, we developed a method for generating performance metrics using a model-based estimation of clearance angles between an object's surface and the carving blade. The calculated clearance angles are compared with desired angles obtained from expert operators. Then, angular errors are presented as tactile cues to the user's finger pads through electrical stimuli at the middle phalanx of the index finger and the thumb. Subsequently, we conducted a feasibility test with novice dental technicians, who showed improvement in initial clearance angles of carving strokes. Moreover, the results showed significant reduction in the occurrence rate of poor-carving when using the proposed system. From these results, we concluded that electrotactile augmentation can provide effective guidance for carving tasks.

Material Roughness Modulation via Electrotactile Augmentation.

Tactile exploration of a material's texture using a bare finger pad is a daily human activity. However, modern tactile displays do not allow users to experience the natural sensations of a material when artificial sensations are presented. We propose an electrotactile augmentation technique capable of superimposing vibrotactile sensations in a finger pad, thereby allowing the texture modulation of real materials. Users attach two stimulus electrodes to the middle phalanx of a finger and a grounded electrode at the base of the finger in order to evoke nerve activity. This paper evaluates the proposed electrotactile augmentation for roughness modulation of real materials. First, we introduce the principle of the electrotactile display, which presents artificial sensations at the finger pad. We then confirm that the perceived frequency of mechanical vibration at the finger pad can be shifted using electrotactile augmentation. Finally, we discuss a user study, wherein participants rated the roughness of real materials explored using the proposed system. Experimental results indicate that fine- and macro-roughness perceptions of real materials can be altered using electrotactile augmentation.

Finger motion capture from wrist-electrode contact resistance.

Hand motion capture is an important yet challenging topic for biomechanics and human computer interaction. We proposed a novel electrical sensing technology for capturing the finger angles from the variation of the wrist shape. The proposed device detects the signal related to the wrist-electrode contact resistances, which change according to the variation of the wrist shape accompanying finger movements. The developed sensing device consists of a wrist band, sixteen electrodes and a sensing circuit of contact resistances. We investigated the relationships between the finger angles and the system outputs by using a glove-type joint angle sensor. As a result, we confirmed high correlations of the system outputs with the finger angles for several electrodes. Therefore, we conclude that the proposed system can be used for the estimation of the finger joint angles.

Unobtrusive tactile sensing based on electromechanical boundary estimation.

Unobtrusive tactile sensing is an important yet challenging topic for medical and robotic fields. We proposed a novel tactile sensing technology for obtaining the force of an interaction and the position at which it makes contact with an object of arbitrary shape without any mechanical obstructions. The proposed sensing method is based on electromechanical boundary estimation from the potential distribution, which is related to the contact state of the two objects with a potential applied. To evaluate the sensing method, we investigated the error of positional estimation and the relationship between force and sensor output. The experimental results indicated that the contact position can be estimated with a correctable systematic error several mm.We also confirmed a high correlation between the interacting force and the system output.

Smart sensing of tool/tissue interaction by resistive coupling.

A smart sensing of tool-tissue interaction is required to monitor the surgical task without disturbing the tool manipulation. We proposed a new tactile sensing method that enables us to detect the tool-tissue interaction with a simple hardware by resistive coupling. The system consists of two electrodes, a bridge circuit and a differential amplifier for the robust sensing of the contact resistance between the tool and tissue. In order to evaluate the sensing method, we investigated the relationship between the sensor output and the deformation of a wet sponge sample by retraction task. According to the model fitting of the deformation-output profile, we concluded that the proposed sensor provide enough reproducibility in the simple situation. Furthermore, we confirmed that the developed sensor works with a biological sample.

Development of a spatially transparent electrotactile display and its performance in grip force control.

An important function for a tactile navigation system of a handheld tool, such as a surgical scalpel, is the spatial transparency of the device. This paper proposed a new tactile display that can augment touch sensation at the finger pulps without the need for a stimulator between the tool and the finger pulps. We utilized transcutaneous electrical nerve stimulation at the middle phalanx of a finger to separate the stimulated and the perceived areas. In order to verify the effects of the spatial transparency, the performances of grip force control were examined. The results indicated that the proposed display was effective in helping the user to maintain the stable control of the grip force when using a handheld tool.