Development of a Pitch Conversion Tactile Display with Spatial Resolution Higher than Human's Two-point Discrimination Ability

The purpose of this study was to determine the limits of two-point discrimination ability in the lower limb in a sample of healthy, young adult men and women. Eleven different areas of skin were tested with a commercially available compass-type instrument to determine the shortest distance at which two simultaneously applied, nonpainful, light-touch stimuli could be perceived. Mean two-point discrimination values in the lower limb ranged from 43.6 mm for skin overlying the medial surface of the leg to 6.6 mm on the plantar surface of the tip of the great toe. The results also demonstrated interindividual variation in two-point discrimination for a given area of skin. In the majority of skin areas tested, mean values obtained from men and women were essentially the same. In several of the test areas, however, women were significantly better than men in their two-point discrimination ability. The observed intraindividual and interindividual variation suggests that although two-point testing is a useful clinical tool, caution is necessary when interpreting the results from patients with alterations in cutaneous sensibility.

Capsaicin-induced impairment of tactile spatial discrimination ability in man: indirect evidence for increased receptive fields in human nervous system

Purpose The purpose of this study is to investigate the change of dynamic and static balance ability and the change of sensory system in the ankle region by wearing shoes with different heel heights. Methods This study was conducted for 30 women attending S university in Namwon city for 4 weeks from September 5, 2016 to October 2, 2016.The study group(n=15) was wearing shoes with a heel height of 7 cm and the control group(n=15) was wearing shoes with a heel height of 3 cm for more than 8 hours per day for 4 weeks.The dynamic balance ability was assessed using the YBalance Test, the static balance ability was assessed using FICSIT, and the sensory identification test was using the twopoint discriminant test. Results Differences in static balance ability within the study group were statistically significant(p<.05). The difference of static balance ability between study group and control group was significant(p<.05). The difference in the twopoint discrimination ability between the study group and the control group was statistically significant(p<.05). Conclusion The group wearing high heeled shoes had low sensitivity to sensation and low static balance ability. Therefore, it is considered that high heeled shoe is difficult to maintain balance by increasing foot fatigue and lowering sense of body.

Amputation of a lower limb not only affects mobility but also interferes with sensory feedback, leading to an elevated risk of falls among individuals living with amputation. Sensory substitution, achieved through tactile displays embedded in transfemoral prosthetic sockets, presents a promising non-invasive solution to provide artificial sensation to users. However, for this approach to be effective, users must accurately perceive distinct combinations of vibrations, a capacity limited by their two-point discrimination ability. This study examined whether spacing two vibrotactile stimuli within the 20-30 mm range, on the thigh, enabled the perception of distinct points and whether vibration frequency affected spatial acuity. We defined the ability to perceive two distinct points as achieving at least a 75% accuracy in responses, and based on this criterion, we determined that the minimum distance required for two-point discrimination lies between 25 mm and 30 mm. Notably, our study revealed that spatial acuity was not altered when vibrating at either low (30 Hz) or high (150 Hz) frequencies, provided the vibrations were at the perceptual threshold. Lastly, our findings consistently favoured stimuli that were spaced out vertically over horizontal ones. These findings contribute to the improvement of tactile displays intended for sensory substitution in transfemoral prostheses.

Sensory discrimination training has demonstrated improvements in two-point discrimination and pain reduction in people with chronic pain. We tested the feasibility and acceptability of a novel Sensory Training System (STS) device in the homes of people with Type 1 Complex Regional Pain Syndrome (CRPS). Participants meeting CRPS diagnostic criteria were invited to use the STS for a minimum of 30minutes per day for 30days. Device usage data were captured by the STS. Assessments at baseline and after 30days were: two-point discrimination ability, pain intensity and interference, sensitivity and emotions towards CRPS limb. Qualitative interviews were conducted at the end of the study to capture participants' feedback on the device. A total of 10 participants (female n = 7) completed the study. Participants' mean age was 56.4years (range: 24-78years), and mean disease duration was 9.37years (range: 4.25-26.5). Eight had lower limb CRPS. The mean STS device use was 27.3 ± 3.4days and mean daily usage of training games was 00:27:11 ± 00:07:52 (hh:mm:ss). No patterns or trends were evident between device usage and outcome data. This feasibility study of a home-based STS for people with CRPS revealed key areas for improvement in the device's hardware and software and outlined the challenges of development and testing during the COVID-19 pandemic, while also capturing valuable usability insights from participant feedback. Key recommendations include early and ongoing collaboration with users, securing sufficient funding, ensuring correct device setup by participants, conducting interim analysis, and using online tools to enhance participant experience and data collection. The study was registered with ISRCTN registry on 28th May 2021 (https://doi.org/10.1186/ISRCTN89099843).

Somesthetic discrimination thresholds in the absence of the corpus callosum

Performance on a manual tracking task differentiates individuals at risk of developing carpal tunnel syndrome from those not at risk

The aim of the present study was to examine the tongue’s stereognostic ability of healthy subject in the absence of visual reference objects. The stereognostic ability of the tongue was assessed by placing 10 different test pieces in the mouth, and subjects were asked to draw the shape of each test piece in their mouths, and the drawings were scored. The average score was 15.6 of 30 possible points, and scores varied among individuals. For comparison, the stereognostic ability was also measured in the presence of visual references; subjects were asked to choose the corresponding shape to each test piece in their mouths among presented pictures of the test pieces. The mean number of correct answers was 9.2 of 10 possible numbers; the presence of visual references dramatically increased the correct response rate and decreased individual variability. To examine what were other tongue functions needed for stereognosis, two-point discrimination and motor ability of the tongue were also investigated. Two-point discrimination was assessed by touching one or two points with fixed distances to the tongue, and asking the subjects to identify how many points were contacted. To assess motor activity, the time to turn over a test piece in the mouth by the tongue was measured. The stereognostic ability of the tongue in the absence of visual references was not correlated significantly with two-point discrimination or the time to turn over a test piece. In conclusion, the assessment in the absence of visual references could detect individual differences in stereognostic ability of the tongue in more detail than the assessment in the presence of visual information. The assessment method without visual information would be helpful in the diagnosis and treatment of patients with dysphagia.

Two-point discrimination threshold is commonly used for assessing tactile spatial resolution. Since the effect of temporal features of cutaneous test stimulation on spatial discrimination ability is not yet well known, we determined whether the ability to discriminate between two stimulus locations varies with the interstimulus interval (ISI) of sequentially presented tactile stimuli or the length of the stimulus train. Electrotactile stimuli were applied to one or two locations on the skin of the thenar eminence of the hand in healthy human subjects. Tactile discrimination ability was determined using methods based on the signal detection theory allowing the assessment of sensory performance, independent of the subject's response criterion. With stimulus pairs, the ability to discriminate spatial features of stimulation (one location vs. two stimulus locations 4 cm apart) was improved when the ISI was equal to or longer than that required for tactile temporal discrimination. With stimulus trains, the ability to discriminate spatial features of stimulation was significantly improved with an increase in the stimulus train (from 3 to 11 pulses corresponding to train lengths from 40 to 200 ms). These results indicate that temporal features of tactile stimulation significantly influence sensory performance in a tactile spatial discrimination task. Precise control of temporal stimulus parameters should help to reduce variations in results on the two-point discrimination threshold.

BackgroundIt has been a great challenge to treat clinical stage 4 Diabetic foot ulcers (DFUs) due to high rates of major amputations and prolonged healing time. This study aimed to assess the effectiveness of a three-stage sequential surgical approach, which based on the Integrated Surgery Wound Treatment (ISWT) mode, to manage clinical stage 4 DFUs and compare the benefit of incorporating tibial cortex transverse transport (TTT) surgery at stage 3 treatment.MethodsTwenty-three patients with clinical stage 4 DFUs aged 45–75 years treated between January 2022 and February 2023 were retrospectively analyzed. Eleven patients (Group A) received wound debridement, antibiotic-loaded bone cement (ALBC) at stage 1 treatment, percutaneous transluminal angioplasty (PTA), wound debridement, and ALBC at stage 2 treatment, and skin grafting with TTT at stage 3 treatment, while twelve patients (Group B) received the same treatment without TTT. Assessed clinical outcomes included length of hospital stay, ulcer healing duration, ulcer recurrence rate, reintervention (re)-PTA rate, amputation rate, mortality rate, visual analog scale (VAS) scores, ankle-brachial index (ABI), and two-point discrimination (2-PD) ability. The computed tomographic angiography (CTA) was used to evaluate vascular hyperplasia.ResultsGroup A showed no occurrences of re-PTA (P = 0.037) and similar ulcer healing times (P = 0.975) compared to Group B. Ulcer outcome, amputation, and mortality rate were also alike in the two groups (P > 0.05). One year after surgery, Group A demonstrated improvement in VAS scores, ABI, and 2-PD, while Group B showed no significant changes. Additionally, Group A exhibited enhanced lower limb artery characteristics compared to Group B.ConclusionThe sequential three-stage approach based on the ISWT mode effectively manages clinical stage 4 DFUs. Incorporating TTT surgery at stage 3 extends the benefits of PTA surgery.

Stimulating Swallowing: Essential Central and Peripheral Nervous System Targets

The goal of this study was to analyze the human ability of external force discrimination while actively moving the arm. With the approach presented here, we give an overview for the whole arm of the just-noticeable differences (JNDs) for controlled movements separately executed for the wrist, elbow, and shoulder joints. The work was originally motivated in the design phase of the actuation system of a wearable exoskeleton, which is used in a teleoperation scenario where force feedback should be provided to the subject. The amount of this force feedback has to be calibrated according to the human force discrimination abilities. In the experiments presented here, 10 subjects performed a series of movements facing an opposing force from a commercial haptic interface. Force changes had to be detected in a two-alternative forced choice task. For each of the three joints tested, perceptual thresholds were measured as absolute thresholds (no reference force) and three JNDs corresponding to three reference forces chosen. For this, we used the outcome of the QUEST procedure after 70 trials. Using these four measurements we computed the Weber fraction. Our results demonstrate that different Weber fractions can be measured with respect to the joint. These were 0.11, 0.13, and 0.08 for wrist, elbow, and shoulder, respectively. It is discussed that force perception may be affected by the number of muscles involved and the reproducibility of the movement itself. The minimum perceivable force, on average, was 0.04 N for all three joints.

This study was performed to assess two-point discrimination ability for skin areas of the face and trunk. Using a compass-type instrument, I determined two-point discrimination values for three areas on the face and eight, nonoverlapping regions of the neck and trunk in a sample of 43 healthy young adult men and women. Mean values for the face ranged from 14.9 mm over the eyebrow to 10.4 mm along the lateral aspect of the mandible. Values for the neck and trunk ranged from 35.2 mm for skin of the lateral neck to 55.4 mm for the region immediately lateral to the C7 spinous process. I also found interindividual variation in two-point discrimination ability for a given skin area. Except for skin overlying the body of the mandible, where values for women were lower than those measured in men, no significant differences in discrimination ability were found between men and women. Although assessment of two-point discrimination is useful in the clinical evaluation of certain types of patients, the existence of intraindividual and interindividual differences suggests that therapists must interpret the results of these tests with caution.

We show that human ability to discriminate the wavelength of monochromatic lightcan be understood as maximum likelihood decoding of the cone absorptions, with asignal processing efficiency that is independent of the wavelength. This work isbuilt on the framework of ideal observer analysis of visual discrimination usedin many previous works. A distinctive aspect of our work is that we highlight aperceptual confound that observers should confuse a change in input lightwavelength with a change in input intensity. Hence a simple ideal observer modelwhich assumes that an observer has a full knowledge of input intensity shouldover-estimate human ability in discriminating wavelengths of two inputs ofunequal intensity. This confound also makes it difficult to consistently measurehuman ability in wavelength discrimination by asking observers to distinguishtwo input colors while matching their brightness. We argue that the bestexperimental method for reliable measurement of discrimination thresholds is theone of Pokorny and Smith, in which observers only need to distinguish twoinputs, regardless of whether they differ in hue or brightness. Wemathematically formulate wavelength discrimination under thiswavelength-intensity confound and show a good agreement between our theoreticalprediction and the behavioral data. Our analysis explains why the discriminationthreshold varies with the input wavelength, and shows how sensitively thethreshold depends on the relative densities of the three types of cones in theretina (and in particular predict discriminations in dichromats). Ourmathematical formulation and solution can be applied to general problems ofsensory discrimination when there is a perceptual confound from other sensoryfeature dimensions.

A device was constructed to assess two-point discrimination in the plantar skin of younger, middle-aged, and older adults. The device consisted of paired filaments, each delivering a tip force of 4.56 log units (equivalent to 3.63 g), at a fixed distance apart. Statistical analysis showed significant differences in two-point discrimination accuracy between these groups of subjects. Younger subjects showed greater accuracy of plantar two-point discrimination than either middle-aged or older subjects, with an apparent inverse linear relationship between subject age and plantar two-point discrimination ability. A model to assess age-related changes in two-point discrimination is presented.