Evaluation and modeling of diaphragm displacement using ultrasound imaging for wearable respiratory assistive robot.

Introduction: Assessing the influence of respiratory assistive devices on the diaphragm mobility is essential for advancing patient care and improving treatment outcomes. Existing respiratory assistive robots have not yet effectively assessed their impact on diaphragm mobility. In this study, we introduce for the first time a non-invasive, real-time clinically feasible ultrasound method to evaluate the impact of soft wearable robots on diaphragm displacement. Methods: We measured and compared diaphragm displacement and lung volume in eight participants during both spontaneous and robotic-assisted respiration. Building on these measurements, we proposed a human-robot coupled two-compartment respiratory mechanics model that elucidates the underlying mechanism by which our extracorporeal wearable robots augments respiration. Specifically, the soft robot applies external compression to the abdominal wall muscles, inducing their inward movement, which consequently pushes the diaphragm upward and enhances respiratory function. Finally, we investigated the level and shape of various robotic assistive forces on diaphragm motion. Results: This robotic intervention leads to a significant increase in average diaphragm displacement by 1.95 times and in lung volume by 2.14 times compared to spontaneous respiration. Furthermore, the accuracy of the proposed respiratory mechanics model is confirmed by the experimental results, with less than 7% error in measurements of both diaphragm displacement and lung volume. Finally, the magnitude of robotic assistive forces positively correlates with diaphragm movement, while the shape of the forces shows no significant relationship with diaphragm activity. Conclusion: Our experimental findings validate the effective assistance mechanism of the proposed robot, which enhances diaphragm mobility and assists in ventilation through extracorporeal robotic intervention. This robotic system can assist with ventilation while increasing diaphragm mobility, potentially resolving the issue of diaphragm atrophy. Additionally, this work paves the way for improved robotic designs and personalized assistance, tailored to the dynamics of the diaphragm in respiratory rehabilitation.

Perceptually Inspired C0-Continuity Haptic Shape Display with Trichamber Soft Actuators.

Shape display devices composed of actuation pixels enable dynamic rendering of surface morphological features, which have important roles in virtual reality and metaverse applications. The traditional pin-array solution produces sidestep-like structures between neighboring pins and normally relies on high-density pins to obtain curved surfaces. It remains a challenge to achieve continuous curved surfaces using a small number of actuated units. To address the challenge, we resort to the concept of surface continuity in computational geometry and develop a C0-continuity shape display device with trichamber fiber-reinforced soft actuators. Each trichamber unit produces three-dimensional (3D) deformation consisting of elongation, pitch, and yaw rotation, thus ensuring rendered surface continuity using low-resolution actuation units. Inspired by human tactile discrimination threshold on height and angle gradients between adjacent units, we proposed the mathematical criteria of C0-continuity shape display and compared the maximal number of distinguishable shapes using the proposed device in comparison with typical pin-array. We then established a shape control model considering the nonlinearity of soft materials to characterize and control the soft device to display C0-continuity shapes. Experimental results showed that the proposed device with nine trichamber units could render typical sets of distinguishable C0-continuity shape sequence changes. We envision that the concept of C0-continuity shape display with 3D deformation capability could improve the fidelity of the rendered shapes in many metaverse scenarios such as touching human organs in medical palpation simulations.

Extracorporeal Closed-Loop Respiratory Regulation for Patients With Respiratory Difficulty Using a Soft Bionic Robot.

OBJECTIVE: Respiratory regulation is critical for patients with respiratory dysfunction. Clinically used ventilators can lead to long-term dependence and injury. Extracorporeal assistance approaches such as iron-lung devices provide a noninvasive alternative, however, artificial actuator counterparts have not achieved marvelous biomimetic ventilation as human respiratory muscles. Here, we propose a bionic soft exoskeleton robot that can achieve extracorporeal closed-loop respiratory regulation by emulating natural human breath. METHODS: For inspiration, a soft vacuum chamber is actuated to produce negative thoracic pressure and thus expand lung volume by pulling the rib cage up and outward through use of external negative pressure. For expiration, a soft origami array under positive pressure pushes the abdominal muscles inward and the diaphragm upward. To achieve in vitro measurement of respiratory profile, we describe a wireless respiratory monitoring device to measure respiratory profiles with high accuracy, validated by quantitative comparisons with spirometer as gold-standard reference. By constructing a human-robot coupled respiratory mechanical model, a model-based proportional controller is designed for continuous tracking of the target respiratory profile. RESULTS: In experiments with ten healthy participants and ten patients with respiratory difficulty, the robot can adjust its assistive forces in real time and drive human-robot coupling respiratory system to track the target profile. CONCLUSION: The biomimetic robot can achieve extracorporeal closed-loop respiratory regulation for a diverse population. SIGNIFICANCE: The soft robot has important potential to assist respiration for people with respiratory difficulty, whether in a hospital or a home setting.

A Multi-Layer Stacked Microfluidic Tactile Display With High Spatial Resolution.

Pneumatic tactile displays dynamically customize surface morphological features with reconfigurable arrays of independently addressable actuators. However, their ability to render detailed tactile patterns or fine textures is limited by the low spatial resolution. For pneumatic tactile displays, the high-density integration of pneumatic actuators within a small space (fingertip) poses a significant challenge in terms of pneumatic circuit wiring. In contrast to the structure with a single-layer layout of pipes, we propose a multi-layered stacked microfluidic pipe structure that allows for a higher density of actuators and retains their independent actuation capabilities. Based on the proposed structure, we developed a soft microfluidic tactile display with a spatial resolution of 1.25 mm. The device consists of a 5 × 5 array of independently addressable microactuators, driven by pneumatic pressure, each of which enables independent actuation of the surface film and continuous control of the height. At a relative pressure of 1000 mbar, the actuator produced a perceptible out-of-plane deformation of 0.145 mm and a force of 17.7 mN. User studies showed that subjects can easily distinguish eight tactile patterns with 96% accuracy.

Group Haptic Collaboration: Evaluation of Teamwork Behavior during VR Four-Person Rowing Task.

The assessment of multi-person group collaboration has garnered increasing attention in recent years. However, it remains uncertain whether haptic information can be effectively utilized to measure teamwork behavior. This study seeks to evaluate teamwork competency within four-person groups and differentiate the contributions of individual members through a haptic collaborative task. To achieve this, we propose a paradigm in which four crews collaboratively manipulate a simulated boat to row along a target curve in a shared haptic-enabled virtual environment. We define eight features related to boat trajectory and synchronization among the four crews' paddling movements, which serve as indicators of teamwork competency. These features are then integrated into a comprehensive feature, and its correlation with self-reported teamwork competency is analyzed. The results demonstrate a strong positive correlation (r>0.8) between the comprehensive feature and teamwork competency. Additionally, we extract two kinesthetic features that represent the paddling movement preferences of each crew member, enabling us to distinguish their contributions within the group. These two features of the crews with the highest and the lowest contribution in each group were significantly different. This work demonstrates the feasibility of kinesthetic features in evaluating teamwork behavior during multi-person haptic collaboration tasks.

Quantitative Identification of ADHD Tendency in Children With Immersive Fingertip Force Control Tasks.

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder that affects children. However, the traditional scale-based diagnosis methods rely more on subjective experiences, leading to a demand of objective biomarkers and quantified diagnostic methods. This study proposes a quantitative approach for identifying ADHD tendency based on fingertip pressing force control paradigm with immersive visual feedback. By extracting nine behavioral features from reaction time and dynamic force fluctuation features with high temporal and amplitude resolution, the proposed method can effectively capture the continuous changes in attention levels for ADHD diagnosis. The extracted features were analyzed using independent sample t-test and Pearson correlation to determine their association with ADHD-RS scale scores. Results showed that 12 statistical indicators were effective for distinguishing ADHD children from typically developed children, and several features of force control ability were also associated with core ADHD symptoms. A support vector machine (SVM) based classifier is trained for ADHD diagnosis and achieved an accuracy of 78.5%. This work provides an objective and quantitative approach for identifying ADHD tendency within a short testing time, and reveals the inherent correlation between the attention levels and the extracted features of reaction time and force fluctuation dynamics.

Voluntary Respiration Control: Signature Analysis by EEG.

The perception of voluntary respiratory consciousness is quite important in some situations, such as respiratory assistance and respiratory rehabilitation training, and the key signatures about voluntary respiration control may lie in the neural signals from brain manifested as electroencephalography (EEG). The present work aims to explore whether there exists correlation between voluntary respiration and scalp EEG. Evoke voluntary respiration of different intensities, while collecting EEG and respiration signal synchronously. Data from 11 participants were analyzed. Spectrum characteristics at low-frequency band were studied. Computation of EEG-respiration phase lock value (PLV) and EEG sample entropy were conducted as well. When breathing voluntarily, the 0-2 Hz band EEG power is significantly enhanced in frontal and right-parietal area. The distance between main peaks belonging to the two signals in 0-2 Hz spectrum graph tends to get smaller, while EEG-respiration PLV increases in frontal area. Besides, the sample entropy of EEG shows a trend of decreasing during voluntary respiration in both areas. There's a strong correlation between voluntary respiration and scalp EEG. Significance: The discoveries will provide guidelines for developing a voluntary respiratory consciousness identifying method and make it possible to monitor people's intention of respiration by noninvasive BCI.

A skin-integrated device for neck posture monitoring and correction.

Cervical spondylosis is a common disease that is often caused by long-term abnormal cervical curvature due to activities such as reading books and using computers or smartphones. This paper explores building an untethered and skin-integrated device in an e-skin form factor to monitor and haptically correct neck posture. The proposed design features a multilayered structure that integrates all flexible electronic circuits and components into a compact skin space while being untethered and skin conformal. An accelerometer in the e-skin attaches to the neck for posture sensing, while four vibration actuators closely touch the neck skin to provide localized vibrotactile stimuli that encode four-direction correction cues of neck flexion ±α and lateral bending ±ß. To ensure the reliability of posture sensing and vibrotactile rendering during neck movement, it is necessary to prevent the e-skin device from shifting position. Thus, a hollow structure-based method is implemented for stably attaching the e-skin to the neck skin. Experiments validated the e-skin device's sensing precision, skin-conformal compliance, stickiness, stability and effectiveness during the motion of neck postures, including its discrimination of localized four-direction vibrotactile cues. A user study verified the device's performance for sensing and correcting different abnormal neck postures during activities such as using smartphones, reading books, and processing computer files. The proposed e-skin device may create opportunities for more convenient cervical spondylosis prevention and rehabilitation.

Survey on Hand-Based Haptic Interaction for Virtual Reality.

Interacting with virtual objects with haptic feedback directly using the user's hand (hand-based haptic interaction) has attracted increasing attention. Due to the high degrees of freedom of the hand, compared with tool-based interactive simulation using a pen-like haptic proxy, hand-based haptic simulation faces greater challenges, mainly including higher motion mapping and modeling difficulty of deformable hand avatars, higher computational complexity of contact dynamics, and nontrivial multi-modal fusion feedback. In this article, we aim to review key computing components for hand-based haptic simulation, and draw out major findings in this direction while analyzing the gaps toward immersive and natural hand-based haptic interaction. To this end, we investigate existing relevant studies on hand-based interaction with kinesthetic and/or cutaneous display in terms of virtual hand modeling, hand-based haptic rendering, and visuo-haptic fusion feedback. By identifying current challenges, we finally highlight future perspectives in this field.

MateJam: Multi-Material Teeth-Clutching Layer Jamming Actuation for Soft Haptic Glove.

Most existing force feedback gloves use rigid exoskeleton with large structural dimensions, making it challenging to meet the future demand of virtual reality (VR) applications for large-scale end users. There is an urgent need to develop soft and ultrathin gloves similar to daily gloves. Different from the idea of regulating the friction between layers, here we propose a multi-material teeth-clutching layer jamming (MateJam) actuator, which can achieve distinctive bending stiffness in free and constrained space. The actuator consists of multi-material layers whose modulus span three orders of magnitude, including flexible substrate layer, limiting layer, rigid micro-teeth clutching structure layer, sliding film boundary layer, and sealed shell layer. In free space, the flexible substrate, and the rigid micro-teeth array structure form flexible hinges, ensuring low resistance. In constrained space, the engagement degree of the rigid micro-teeth array is controlled by vacuum pressure to continuously adjust the output resistance. Reliable switching between free and constrained space is ensured by introducing the sliding film boundary layer and the optimized design of the micro-teeth cross-sectional shape. The force output ratio between free and constrained space reaches over 20 times (0.45N vs. 11.95N). The thickness of the actuator is as low as 3.8mm (clutched state), and the weight of the glove is 44.03g. The ultrathin formfactor and the low cost fabrication process makes the MateJam glove a promising solution for VR applications in home entertainment and social interactions.

Perceptual Localization Performance of the Whole Hand Vibrotactile Funneling Illusion.

Funneling illusion refers to a midway perceived illusory tactile sensation between multiple distant stimulations. Since haptic illusion provides guidelines to simplify tactile interfaces, funneling illusion has been explored on different parts of human skin. This study aimed to evaluate the perceptual localization performance of vibrotactile funneling illusion on palmar side of the hand. It is based on the idea of leveraging the vibrotactile funneling illusion to produce distributed vibrotactile stimuli across the entire hand using only a few vibration actuators. By designing a glove with actuators on five fingertips and the palm heel, we measured the localization density of funneling illusion on the whole hand in two experimental conditions [one-dimensional (1D) illusion along each finger and 2D illusion on palmar plane]. The results showed that the average correct rate of location discrimination was 97%, 82%, and 71% in 3-, 4-, and 5-location densities for 1D illusion and 85%, 70%, and 58% in 11-, 16-, and 21-location densities for 2D illusion, respectively. These findings confirmed the feasibility of simulating multi-location stimuli using only a few actuators. Also, perceptual guidelines were provided for the designing of vibrotactile gloves by leveraging the entire hand funneling illusion.

Configuration-based Optimization for Virtual Hand Haptic Simulation.

Interacting with virtual objects via haptic feedback using the user's hand directly (virtual hand haptic interaction) provides a natural and immersive way to explore the virtual world. It remains a challenging topic to achieve 1 kHz stable virtual hand haptic simulation with no penetration amid hundreds of hand-object contacts. In this paper, we advocate decoupling the high-dimensional optimization problem of computing the graphic-hand configuration, and progressively optimizing the configuration of the graphic palm and fingers, yielding a decoupled-and-progressive optimization framework. We also introduce a method for accurate and efficient hand-object contact simulation, which constructs a virtual hand consisting of a sphere-tree model and five articulated cone frustums, and adopts a configuration-based optimization algorithm to compute the graphic-hand configuration under non-penetration contact constraints. Experimental results show both high update rate and stability for a variety of manipulation behaviors. Non-penetration between the graphic hand and complex-shaped objects can be maintained under diverse contact distributions, and even for frequent contact switches. The update rate of the haptic simulation loop exceeds 1 kHz for the whole-hand interaction with about 250 contacts.

fNIRS-based adaptive visuomotor task improves sensorimotor cortical activation.

Objective. Investigating how to promote the functional activation of the central sensorimotor system is an important goal in the neurorehabilitation research domain. We aim to validate the effectiveness of facilitating cortical excitability using a closed-loop visuomotor task, in which the task difficulty is adaptively adjusted based on an individual's sensorimotor cortical activation.Approach. We developed a novel visuomotor task, in which subjects moved a handle of a haptic device along a specific path while exerting a constant force against a virtual surface under visual feedback. The difficulty levels of the task were adapted with the aim of increasing the activation of sensorimotor areas, measured non-invasively by functional near-infrared spectroscopy. The changes in brain activation of the bilateral prefrontal cortex, sensorimotor cortex, and the occipital cortex obtained during the adaptive visuomotor task (adaptive group), were compared to the brain activation pattern elicited by the same duration of task with random difficulties in a control group.Main results.During one intervention session, the adaptive group showed significantly increased activation in the bilateral sensorimotor cortex, also enhanced effective connectivity between the prefrontal and sensorimotor areas compared to the control group.Significance.Our findings demonstrated that the functional near-infrared spectroscopy-based adaptive visuomotor task with high ecological validity can facilitate the neural activity in sensorimotor areas and thus has the potential to improve hand motor functions.

Interfinger Synchronization Capability of Paired Fingers in Discrete Fine-Force Control Tasks.

This study examined whether within-a-hand and between-hands finger pairings would exhibit different interfinger synchronization capabilities in discrete fine-force control tasks. Participants were required to perform the designed force control tasks using finger pairings of index and middle fingers on one or two hands. Results demonstrated that the delayed reaction time and the timing difference of paired fingers showed a significant difference among finger pairings. In particular, paired fingers exhibited less delayed reaction time and timing difference in between-hands finger pairings than in within-a-hand finger pairings. Such bimanual advantage of the pairings with two symmetric fingers was evident only in the task types with relatively high amplitudes. However, for a given finger pairing, the asymmetric amplitude configuration, assigning a relatively higher amplitude to either left or right finger of paired fingers, has no significant effect on the interfinger synchronization. Therefore, paired fingers on both hands showed a bimanual advantage in the relatively high force, especially for the pairing of symmetrical fingers, whereas asymmetric amplitude configuration for a finger pairing was able to suppress the bimanual advantage. These findings would enrich the understanding of the interfinger synchronization capability of paired fingers and be referential for interactive engineering applications when leveraging the interfinger synchronization capability in discrete fine-force control tasks.

Hap-pulse: A Wearable Vibrotactile Glove for Medical Pulse Wave Rendering.

Pulse palpation is an important procedure that allows a physician to rapidly assess the status of a patient's cardiovascular system. This paper explores the possibility of using vibrotactile stimuli to render fine temporal profiles of pulse pressure waves. A lightweight wearable vibrotactile glove, called Hap-pulse, is designed to render fine pulse waves through vibrotactile stimuli on users' fingertips. To preserve the fine features of original pulse waves, models are fitted from real pulse wave data (photoplethysmogram (PPG) pulse waveform database), using fourth-order polynomial functions. A square wave envelope mapping algorithm is proposed to produce vibration amplitudes of Linear Resonance Actuators (LRAs), which aims to render the detailed waveform of systolic and diastolic blood pressure states. Evaluation results suggest that Hap-pulse can render pulse waves with an average correlation coefficient 97.84%. To validate the distinguishability and fidelity of Hap-pulse's palpation rendering, a user study consisting of traditional Chinese medicine doctors and unskilled students is conducted. The correct recognition rate of identifying four typical pulse waves is 87.08% (doctors), 57.50% (untrained students) and 79.59% (trained students). These results indicate a novel application of rendering subtle pulse wave signals with vibrotactile gloves, which illustrates the potential of simulating patient palpation training in virtual or remote medical diagnosis.

Soft Exoskeleton Mimics Human Cough for Assisting the Expectoration Capability of SCI Patients.

This paper describes the design of a bionic soft exoskeleton and demonstrates its feasibility for assisting the expectoration function rehabilitation of patients with spinal cord injury (SCI). METHODS: A human-robot coupling respiratory mechanic model is established to mimic human cough, and a synergic inspire-expire assistance strategy is proposed to maximize the peak expiratory flow (PEF), the key metric for promoting cough intensity. The negative pressure module of the exoskeleton is a soft "iron lung" using layer-jamming actuation. It assists inspiration by increasing insufflation to mimic diaphragm and intercostal muscle contraction. The positive pressure module exploits soft origami actuators for assistive expiration; it pressures human abdomen and bionically "pushes" the diaphragm upward. RESULTS: The maximum increase in PEF ratios for mannequins, healthy participants, and patients with SCI with robotic assistance were 57.67%, 278.10%, and 124.47%, respectively. The soft exoskeleton assisted one tetraplegic SCI patient to cough up phlegm successfully. CONCLUSION: The experimental results suggest that the proposed soft exoskeleton is promising for assisting the expectoration ability of SCI patients in everyday life scenarios. SIGNIFICANCE: The proposed soft exoskeleton is promising for advancing the application field of rehabilitation exoskeletons from motor functions to respiratory functions.

Effect of force accuracy on hemodynamic response: an fNIRS study using fine visuomotor task.

Objective. Despite converging neuroimaging studies investigating how neural activity is modulated by various motor related factors, such as movement velocity and force magnitude, little has been devoted to identifying the effect of force accuracy. This study thus aimed to investigate the effect of task difficulty on cortical neural responses when participants performed a visuomotor task with varying demands on force accuracy.Approach. Fourteen healthy adults performed a set of force generation operations with six levels of force accuracy. The participants held a pen-shaped tool and moved the tool along a planar ring path, meanwhile producing a constant force against the plane under visual guidance. The required force accuracy was modulated by allowable tolerance of the force during the task execution. We employed functional near-infrared spectroscopy to record signals from bilateral prefrontal, sensorimotor and occipital areas, used the hemoglobin concentration as indicators of cortical activation, then calculated the effective connectivity across these regions by Granger causality.Main results.We observed overall stronger activation (oxy-hemoglobin concentration,p= 0.015) and connectivity (p< 0.05) associated with the initial increase in force accuracy, and the diminished trend in activation and connectivity when participants were exposed to excessive demands on accurate force generation. These findings suggested that the increasing task difficulty would be only beneficial for the mental investment up to a certain point, and above that point neural responses would show patterns of lower activation and connections, revealing mental overload at excessive task demands.Significance.Our results provide the first evidence for the inverted U-shaped effect of force accuracy on hemodynamic responses during fine visuomotor tasks. The insights obtained through this study also highlight the essential role of inter-region connectivity alterations for coping with task difficulty, enhance our understanding of the underlying motor neural processes, and provide the groundwork for developing adaptive neurorehabilitation strategies.

EEG Correlates of Sustained Attention Variability during Discrete Multi-finger Force Control Tasks.

The neurophysiological characteristics of sustained attention states are unclear in discrete multi-finger force control tasks. In this article, we developed an immersive visuo-haptic task for conducting stimulus-response measurements. Visual cues were randomly provided to signify the required amplitude and tolerance of fingertip force. Participants were required to respond to the visual cues by pressing force transducers using their fingertips. Response time variation was taken as a behavioral measure of sustained attention states during the task. 50% low-variability trials were classified as the optimal state and the other high-variability trials were classified as the suboptimal state using z-scoring over time. A 64-channel electroencephalogram (EEG) acquisition system was used to collect brain activities during the tasks. The haptics-elicited potential amplitude at 20 ∼ 40 ms in latency and over the frontal-central region significantly decreased in the optimal state. Furthermore, the alpha-band power in the spectra of 8 ∼ 13 Hz was significantly suppressed in the frontal-central, right temporal, and parietal regions in the optimal state. Taken together, we have identified neuroelectrophysiological features that were associated with sustained attention during multi-finger force control tasks, which would be potentially used in the development of closed-loop attention detection and training systems exploiting haptic interaction.

Using convolutional neural networks to decode EEG-based functional brain network with different severity of acrophobia.

Objective.The prevalence of acrophobia is high, especially with the rise of many high-rise buildings. In the recent few years, researchers have begun to analyze acrophobia from the neuroscience perspective, especially to improve the virtual reality exposure therapy (VRET). Electroencephalographic (EEG) is an informative neuroimaging technique, but it is rarely used for acrophobia. The purpose of this study is to evaluate the effectiveness of using EEGs to identify the degree of acrophobia objectively.Approach.EEG data were collected by virtual reality (VR) exposure experiments. We classified all subjects' degrees of acrophobia into three categories, where their questionnaire scores and behavior data showed significant differences. Using synchronization likelihood, we computed the functional connectivity between each pair of channels and then obtained complex networks named functional brain networks (FBNs). Basic topological features and community structure features were extracted from the FBNs. Statistical results demonstrated that FBN features can be used to distinguish different groups of subjects. We trained machine learning (ML) algorithms with FBN features as inputs and trained convolutional neural networks (CNNs) with FBNs directly as inputs.Main results.It turns out that using FBN to identify the severity of acrophobia is feasible. For ML algorithms, the community structure features of some cerebral cortex regions outperform typical topological features of the whole brain, in terms of classification accuracy. The performances of CNN algorithms are better than ML algorithms. The CNN with ResNet performs the best (accuracy reached 98.46 ± 0.42%).Significance.These observations indicate that community structures of certain cerebral cortex regions could be used to identify the degree of acrophobia. The proposed CNN framework can provide objective feedback, which could help build closed-loop VRET portable systems.

Effect of Temperature on the Absolute and Discrimination Thresholds of Voltage on Electrovibration Tactile Display.

Multi-dimensions tactile displays, such as thermal and texture display, are desirable for enhancing perception while users experience virtual shopping such as touching a garment in virtual reality. Understanding the effect of one dimension on the other is fundamental for design of multi-dimensions tactile display. In this article, we report the effect of temperature on thresholds of voltage applied on an electrovibration tactile display. Three temperatures of the electrovibration tactile display at 18°C (cold), 30°C (neutral) and 38°C (warm) were considered in two experiments. In Experiment I, we measured the absolute thresholds of square wave voltage with 25 Hz, 140 Hz and 485 Hz. In Experiment II, we measured the amplitude discrimination thresholds of same voltage signals as in Experiment I. The results show that the absolute thresholds differed significantly between 18°C and 38°C for all the three frequencies. No significant difference in the absolute threshold was found between 18°C and 30°C, except for the 485 Hz voltage. The amplitude discrimination thresholds were essentially constant except for that of the 485 Hz voltage at 18°C, which were 17.11 Vpp and 16.86 Vpp larger than those at 30°C and 38°C, respectively.