Two-point Threshold Research Articles

Artificial Tactile Sensory Finger for Contact Pattern Identification Based on High Spatiotemporal Piezoresistive Sensor Array.

Human fingertip tactile perception relies on the activation of densely distributed tactile receptors to identify contact patterns in the brain. Despite significant efforts to integrate tactile sensors with machine learning algorithms for recognizing physical patterns on object surfaces, developing a tactile sensing system that emulates human fingertip capabilities for identifying contact patterns with a high spatiotemporal resolution remains a formidable challenge. In this study, we present the development of an artificial tactile finger for accurate contact pattern identification, achieved through the integration of a high spatiotemporal piezoresistive sensor array (PRSA) and a convolutional neural network (CNN) model. Spatiotemporal characterization tests reveal that the artificial finger exhibits a fast temporal resolution of approximately 7 ms and achieves a two-point threshold of 1.5 mm, surpassing that of the human fingertip. To compare the performance of the artificial finger with the human finger in recognizing different patterns, we acquired pressure images by pressing the artificial finger, coated with a flexible PRSA film, onto both simple embossed and complex curved patterns while also recording human recognition results of perceiving these patterns. Experimental findings demonstrate that the artificial finger achieves higher classification accuracy in recognizing both simple and complex patterns (99.0 and 96.1%, respectively) compared to the human fingertip (69.1 and 22.7%). This artificial finger serves as a promising platform with great potential for various robotic tactile sensing applications including prosthetics, skin electronics, and robotic surgery.

Performance of plasma p-tau217 for the detection of amyloid-β positivity in a memory clinic cohort using an electrochemiluminescence immunoassay

BackgroundPlasma p-tau217 has emerged as the most promising blood-based marker (BBM) for the detection of Alzheimer Disease (AD) pathology, yet few studies have evaluated plasma p-tau217 performance in memory clinic settings. We examined the performance of plasma p-tau217 for the detection of AD using a high-sensitivity immunoassay in individuals undergoing diagnostic lumbar puncture (LP).MethodsPaired plasma and cerebrospinal fluid (CSF) samples were analysed from the TIMC-BRAiN cohort. Amyloid (Aβ) and Tau (T) pathology were classified based on established cut-offs for CSF Aβ42 and CSF p-tau181 respectively. High-sensitivity electrochemiluminescence (ECL) immunoassays were performed on paired plasma/CSF samples for p-tau217, p-tau181, Glial Fibrillary Acidic Protein (GFAP), Neurofilament Light (NfL) and total tau (t-tau). Biomarker performance was evaluated using Receiver-Operating Curve (ROC) and Area-Under-the-Curve (AUC) analysis.ResultsOf 108 participants (age: 69 ± 6.5 years; 54.6% female) with paired samples obtained at time of LP, 64.8% (n = 70/108) had Aβ pathology detected (35 with Mild Cognitive Impairment and 35 with mild dementia). Plasma p-tau217 was over three-fold higher in Aβ + (12.4 pg/mL; 7.3—19.2 pg/mL) vs. Aβ- participants (3.7 pg/mL; 2.8—4.1 pg/mL; Mann–Whitney U = 230, p < 0.001). Plasma p-tau217 exhibited excellent performance for the detection of Aβ pathology (AUC: 0.91; 95% Confidence Interval [95% CI]: 0.86–0.97)—greater than for T pathology (AUC: 0.83; 95% CI: 0.75–0.90; z = 1.75, p = 0.04). Plasma p-tau217 outperformed plasma p-tau181 for the detection of Aβ pathology (z = 3.24, p < 0.001). Of the other BBMs, only plasma GFAP significantly differed by Aβ status which significantly correlated with plasma p-tau217 in Aβ + (but not in Aβ-) individuals. Application of a two-point threshold at 95% and 97.5% sensitivities & specificities may have enabled avoidance of LP in 58–68% of cases.ConclusionsPlasma p-tau217 measured using a high-sensitivity ECL immunoassay demonstrated excellent performance for detection of Aβ pathology in a real-world memory clinic cohort. Moving forward, clinical use of plasma p-tau217 to detect AD pathology may substantially reduce need for confirmatory diagnostic testing for AD pathology with diagnostic LP in specialist memory services.

Tongue Reconstruction with Buccinator Myomucosal Island Flaps: Technical Considerations, Oncologic Safety, Functional Outcomes and QoL Assessment-A Retrospective Observational Study.

The objective of this study was to investigate the effectiveness of buccinator myomucosal island flaps for tongue reconstruction following malignant tumor resections. A retrospective study was performed on 52 patients who underwent tongue reconstructions with buccinator myomucosal island flaps between 2012 and 2020. We reviewed the flap type and size, harvesting time, recipient- and donor-site complications, postoperative oncologic outcomes, functional recovery and QoL assessment. All of the flaps were transposed successfully without any total flap loss. Neither in the primary site nor in the neck were cancer relapses observed. An evaluation of the sensitivity revealed that 96.1% of patients experienced a recovery of touch, two-point and pain sensations. There were significant differences between the flap and the native mucosa in terms of the tactile (p < 0.001), pain (p < 0.001) and two-point (p < 0.001) thresholds. The average swallowing score recorded was 6.1 out of 7, with only minor complaints. The quality of life assessments demonstrated high scores across physical (24.5 out of 28), social (25.8 out of 28), emotional (20.3 out of 24) and functional (25 out of 28) aspects. The present study showed how buccinator myomucosal island flaps represent an effective and functional tongue reconstructive option, requiring a short operative time with a low rate of donor site morbidity, and with evidence of long-term oncologic safety and high quality of life.

TWO-POINT DISCRIMINATION ON THE PALMAR SURFACE OF HANDS IN MBBS STUDENTS: INFLUENCE OF BMI, GENDER AND AVERAGE VALUES

Aim: In our study, we attempted to measure the average two-point discrimination values on the pulp of all distal phalanges and the mid-palmar surface of the hands of Healthy MBBS Students and its inuence on BMI and Gender. Study Population &amp; Methodology: We conducted this experiment using a two-point esthesiometer on 100 healthy 1st MBBS students (Females 52, Males 48) aged between 18-20 years from Guntur Medical College, Andhra Pradesh. Based on the BMI we classied subjects under ve categories as per WHO ASIAN-BMI SCALE. Results: Average two-point threshold value in females for right and left rst distal phalanx 3mm, 2.76mm, for second distal phalanx 1.92mm, 2.38mm, for third distal phalanx 2.69mm, 2.26mm fourth distal phalanx 2.84mm, 2.38mm, fth distal phalanx 3.30mm, 2.84mm, mid palmar surface 6mm, 6.76mm respectively. From our study, the two-point threshold is more for the mid-palmar surface. Two-point discrimination has a positive correlation between the right and left palmar surface of the hand but the relationship between variables is weak in the distal phalanges and moderate in the mid-palmar surface. As per BMI, the Two-point discrimination threshold has a positive correlation in the left rst distal phalanx, right and left fourth distal phalanges, right fth distal phalanx and right mid palmar surface. We see an association between gender and the two-point discrimination threshold in the right and left rst distal phalanx and the remaining areas don't have any association.

Psychophysical Studies of Interleaving Narrowband Tactile Stimuli to Achieve Broadband Perceptual Effects

Despite the ubiquitous presence of tactile actuators (tactors) in mobile devices, there is a continuing need for more advanced tactors that can cover the entire frequency range of human tactile perception. Broadband tactors can increase information transmission and enrich sensory experience. The engineering challenges are multifold in that the ideal tactors should exhibit an effective bandwidth of at least 300 Hz, small form factor, robustness, power efficiency and low cost. For wearable applications, there are the additional challenges of ease of mounting and maintaining adequate skin contact during body movements. We propose an approach to interleave narrowband tactile stimuli to achieve broadband effects, taking advantage of the limited spatial resolution of the skin on the torso and limbs. Three psychophysical experiments were conducted to assess the validity of this approach. Participants performed pairwise discriminations of two broadband stimuli delivered using one or two tactors. The broadband stimuli consisted of one mid-frequency and one high-frequency component delivered through one tactor by mixing the two components, or through two tactors (one component per tactor). The first two experiments revealed extraneous cues such as localization and mutual masking of mid- and high-frequency components that were subsequently eliminated in the third experiment. Results from 12 participants confirmed that performance on pairwise comparisons was below the discrimination threshold, confirming that broadband haptic effects can be achieved through narrowband tactors placed within the skin’s two-point limen.

Blue-Light Filtering Intraocular Implants and Darker Irises Reduce the Behavioral Effects of Higher-Order Ocular Aberrations

PurposeHigher order ocular aberrations (e.g. entopic scatter) arising from cornea and lens, decreases retinal image contrast by dispersing part of the image-forming optics over a broad retinal surface. Selective filtering of the light that is most susceptible to aberration (high-energy “blue” light) may reduce some of the behavioral effects. This was tested by comparing the performance of a blue-light filtering (BLF) vs a clear intraocular lens implant (IOL).Methods52 participants with IOL (BLF: AlconSN60AT; clear: AlconSA60AT; N = 98 test eyes; M = 67.33 ± 7.48 years; 58.8% Female; 25.5% non-White) were recruited. Our outcome measure was based on the minimum resolvable distance between two points of light (two-point thresholds), formed using broadband xenon or isolated short-wave energy (425 nm). Iris color was measured by visual inspection and comparison against standard images.ResultsIn the broadband condition, patients with BLF IOL had smaller two-point thresholds (M = 17.17 ± 5.71 mm; F[1,48] = 2.60; p = 0.045) than clear controls (M = 20.93 ± 10.22 mm). Similar improvements were found in the short-wave condition (MBLF=17.02 ± 5.30; Mclear=21.42 ± 10.99; p = 0.04). In the contralateral broadband comparison, eyes with the BLF had significantly smaller two-point thresholds (M = 18.10 ± 10.47 mm; t = −2.90, p < 0.001) than the clear IOL (M = 20.89 ± 10.61 mm). Similar effects were seen in the short-wave condition (MBLF=18.23 ± 9.88; Mclear = 21.06 ± 10.47; p = 0.001). Darker iris color was related to reduced scatter across IOL types, in both shortwave (F[2,48] = 4.62, p = 0.02) and broadband (F[2,48] = 5.27, p = 0.009) conditions.ConclusionsAnterior screening, be it by a darker iris or a BLF IOL, is directly related to decreases in two-point light thresholds.

P103 Minimal Clinically Important Difference (MCID) for the Ulcerative Colitis Patient-Reported Outcomes Signs and Symptoms (UC-PRO/SS) Tool

Abstract Background The UC-PRO/SS tool developed by the IBD PRO Consortium is undergoing FDA Drug Development Tool qualification (COA DDT# 000040). Derivation of minimal clinically important difference (MCID) thresholds for improvement in bowel and functional signs and symptoms domain scores are presented here. Methods MCID estimates for bowel and functional domains were derived using anchor- and distribution-based approaches applied to data from three studies of Etrolizumab. Initial MCIDs were developed using Mayo Clinic Score (MCS) and Inflammatory Bowel Disease Questionnaire (IBDQ) response thresholds as anchors; Cronbach’s alpha SEM and Cohen’s moderate effect size statistics were calculated. MCIDs were then cross-validated internally and externally, i.e. within and across target populations, using clinical (modified and partial MCS) and patient-centered (IBDQ “general wellness” item 10 and EQ5D VAS) measures, to support generalizability. CDF plots with pooled data provide further empirical support. Results Study populations had mean ages of 39.2–40.5 years; were 54.5–58% male; 77.5–93.9% white; and had mean disease duration of 8.75–8.98 years. Six points was selected as the bowel domain threshold as change of this magnitude aligns with the anchor settings (5.89, 6.93, and 7.15 for IBDQ and 5.63, 6.12, and 7.63 for MCS) and exceeds measurement error as shown by distributional methods (Cronbach’s alpha SEM 2.071, 2.160, and 2.167, Cohen’s moderate effect size range 2.086, 2.135, and 2.191). A two-point threshold was similarly selected for the functional domain based on anchor settings (1.77, 1.98, and 2.53 for IBDQ and 1.56, 1.68, and 2.01 for MCS) and distributional methods (Cronbach’s alpha SEM 1.336,1.140, and 1.417, Cohen’s moderate effect size range 1.204, 1.270, and 1.309). External, cross-validation showed numerically robust differences (no overlapping CI’s) between the group achieving the MCID versus not across clinical and PRO variables for both domains. Magnitudes of change on IBDQ item 10 and EQ5D VAS variables scores exceeded the ½ SD for interpreting moderate levels of PRO score change. For the bowel domain, separation of CDF curves between responder groups showed cumulative percentages of approximately 60% and 70% based on IBDQ and MCS anchors, respectively, at the thresholds indicating change of a six-point magnitude. For the functional domain, separation between CDF curves at the 2-point threshold occurred at points indicating cumulative proportions of response greater than 50% using both anchors. Conclusion MCIDs of 6 and 2 points for the bowel and functional domains of the UC-PRO/SS are robustly defined and cross-validated, allowing interpretation of clinical improvement in symptoms among moderate to severe adult UC patients.

다중센싱 진동 인터페이스: 웨어러블 기기의 UX에 미치는 영향을 중심으로

Objective: Based on the two points threshold of vibration stimulation, this paper determines the vibration stimulation type and design variables of the Multi-sensing Vibration Interface. and performs the verification of whether it is compatible with the actual cognitive direction when directional information is provided to the wrist using Multi-sensing wearable device designed on the basis of these results.BRBRBackground: Most of the dangerous situations around us are accompanied by noise. However, pedestrians who are unable to use their hearing, such as hearing-impaired and distracted pedestrians, are unable to recognize latent danger with being exposed to major accidents. Therefore, there is a need for an intuitive and effective way to provide the direction of hazardous situations accompanied by noise to those who cannot use hearing.BRBRMethod: This paper consists of two experiments. In the first experiment, through the two-point threshold experiment of the vibration stimulation, the efficient arrangement of vibration stimulation of the multi-sensing wearable device and the type of providing the vibration stimulation were derived. In the second experiment, when direction information was provided to the user

Tactile Semiautomatic Passive-Finger Angle Stimulator (TSPAS).

Passive tactile perception is the ability to passively and statically perceive stimulus information coming from the skin; for example, the ability to sense spatial information is the strongest in the skin on the hands. This ability is termed tactile spatial acuity, and is measured by the tactile threshold or discrimination threshold. At present, the two-point threshold is extensively used as a measure of tactile spatial acuity, although many studies have indicated that critical deficits exist in two-point discrimination. Therefore, a computer-controlled tactile stimulus system was developed, the tactile semiautomated passive-finger angle stimulator (TSPAS), using the tactile angle discrimination threshold as a new measure for tactile spatial acuity. The TSPAS is a simple, easily operated system that applies raised angle stimuli to a subject's passive fingerpad, while controlling movement speed, distance, and contact duration. The components of the TSPAS are described in detail as well as the procedure to calculate the tactile angle discrimination threshold.

The Effects of a Senofilcon A Contact Lens With and Without a Photochromic Additive on Positive Dysphotopsia Across Age.

Objective:The visual effects of wearing a photochromic contact lens (test) were directly compared with a nonphotochromic contact lens (control). Positive dysphotopsia (halos, starbursts) and intraocular scatter (behaviorally determined) were assessed. Both younger and middle-aged subjects were evaluated to examine the influence of age.Methods:Fifty-four subjects (18–62 years) were tested using a contralateral design. Subjects were fit with a photochromic contact lens on one eye and a nonphotochromic contact lens on the other eye, randomly assigned. Testing occurred with and without photochromic activation (darkened) by use of a violet activator (365 nm, half-bandwidth 20 nm). The extent of dysphotopsia (halos and spokes) was measured using an aperture (∼4 mm) that created a bright point source of light 45 inches from the plane of the eye. Between the point source and subject, a centering precision caliper was used to measure lateral spread. Two-point thresholds were determined by measuring the minimum distance between two points of broadband xenon light.Results:The photochromic contact lens produced smaller halo diameters than the control contact lens, both activated (41% on average) and inactivated (21% on average), and age strata was a significant factor (P<0.001) with the older group showing a greater reduction. The photochromic contact lens produced smaller starburst diameters than the control contact lens, both activated (37% on average) and inactivated (23% on average), and age strata was a significant factor (P=0.001) with the older group showing a greater reduction. The two-point thresholds were reduced (25% activated, 9% inactivated) on average but the age effect was not significant (P<0.10).Conclusions:The senofilcon A lens with photochromic additive reduced the extent of positive dysphotopsia compared with the same lens without the additive, regardless whether the lens was activated or not. The visual benefit was greatest with the older subjects.

Two-point discrimination test. A valuable part of hand surgical rehabilitation, e.g. in tetraplegia

In assessing the prospects for surgical and other kinds of rehabilitation in tetraplegia and stroke patients the two-point discrimination test, correctly performed by experienced examiners, is of great value. Valid and repeatable results depend on exact technique and proper tools. There is a firm correlation between the thresholds of two-point discrimination on the pulps of the fingers and the accuracy of position sense at the metacarpophalangeal and interphalangeal joints. Microneurography has shown that cutaneous receptors have proprioceptive as well as exteroceptive functions. Thus the two-point discrimination test can be used as a measure of proprioceptive function. The results can be expressed numerically. A two-point threshold less than 10 mm on the pulp is a valid measure of useful finger proprioception. It also shows tactile gnosis, necessary for precision sensory grips.

The effects of light scatter when using a photochromic vs. non-photochromic contact lens

PurposeTo assess the visual effects of wearing both an activated and an inactivated photochromic contact lens, with a direct comparison to a non-photochromic contact lens worn in the fellow eye. This study focused on the visual effects of scatter quantified as the minimum distance between two points of light, and the diameter of the halo and starbursts that surround a bright white point source. Methods60 subjects (aged 18–65 years) were measured in a contralateral design where lens type was randomly assigned, one type to each eye. During activated testing, all visual measures of both study lenses were made while each eye was illuminated by a violet (λmax=365, half bandwidth 20nm) activator, which caused steady-state activation of the photochromic lens during the period of testing. Two-point thresholds were determined by measuring the minimum distance between two points of broadband xenon light. Glare geometry was measured using an aperture (∼4mm) that created a bright point source of light 45 inches from the plane of the eye. Between the point source and subject, a centering precision caliper was used to measure lateral spread of halos (diffusion around the source) and visual spokes. The head was stabilized using an adjustable head-rest assembly and the eye was aligned and monitored with a bore camera. ResultsCompared to the non-photochromic lens, and based on the stimulus conditions used in these measurements, the activated and inactivated photochromic lens reduced the light spread using the two-point threshold technique by 32% and 19% respectively; the diameter of the halos were reduced by 44% and 16% respectively; and the spokes were narrowed by 39% and 20% respectively. Based on 95% confidence interval testing, these effects were all statistically significant (p<0.05). ConclusionsThese results are consistent with previous data showing that soft contact lenses with a photochromic additive can improve many aspects of visual function, consistent with their level or activation. Our past data focused on visual function under bright light conditions (e.g., glare disability, discomfort, photostress recovery and chromatic contrast) with an activated photochromic. In this study, we found differences even in the inactivated state, using less intense stimuli (10cd/m2 at the source). This suggests that the photochromic lens improves the effects of light scatter even at lower luminance.

Sensory function in headache: a comparative study among patients with cluster headache, migraine, tension-type headache, and asymptomatic subjects.

Studies evaluating sensory function of the entire trigeminocervical region in patients with cluster headache (CH), migraine (MH), and tension-type headache (TH) are required. The purpose of the present study was to evaluate and compare sensory function in the trigeminocervical region in patients with CH, MH, and TH and healthy controls (HC). Quantitative sensory testing (QST), including pressure pain threshold (PPT), tactile detection threshold (TDT), prick detection threshold (PDT), and two-point detection threshold (2PDT), was evaluated in 139 patients with headache (CH = 16, MH = 52, TH = 71) and 30 HC. Test sites included bilaterally the first, second, and third divisions of trigeminal nerve (V1, V2, and V3), cervical spine, and thenar eminence. TH presented significantly lower PPT values compared with CH (p < 0.015), MH (p < 0.048), and HC (p < 0.009), while MH demonstrated significantly lower values than HC (p = 0.001-0.023). When analyzing TDT, CH in the symptomatic side presented significantly higher values in V1 compared with MH (p = 0.001), TH (p < 0.001), and HC (p < 0.001) and in V2 compared with TH (p = 0.035). No statistically significant differences were found for PDT (p > 0.005). With regard to 2PDT, CH-s presented significantly higher values in V1 with respect to HC (p = 0.016) but lower values in V2 compared with MH (p < 0.001) and TH (p = 0.003). The results of the present study indicate specific and different altered mechanical sensory thresholds in CH, MH, and TH patients compared with HC subjects.

Association between Plasmodium falciparum malaria and the mental disorders in children between five and 19 years in sub-Saharan Africa: a systematic review

Background Mental disorders, also called psychiatric disorders, refer to unconventional or anomalous behavioral patterns, feelings, thoughts, perceptions and beliefs that cause distress or disability, and which are not developmentally or socially acceptable. Plasmodium falciparum (P. falciparum) malaria is the most common parasitic infection of the central nervous system and sub-Saharan Africa has the highest burden of this disease. Children living in this region of the world bear the brunt of P. falciparum malaria and neurological complications commonly associated with it. Objectives The objective of this review was to synthesize the best available evidence on the association of P. falciparum malaria and the short-term and long-term mental disorders of children. Inclusion criteria Types of participants Study participants aged five to 19 years who were residing in sub-Saharan Africa. Types of intervention(s)/phenomena of interest This review considered studies that examined the association between P. falciparum malaria (cerebral malaria, repetitive uncomplicated malaria or asymptomatic malaria) as exposure and a range of mental disorders as an outcome. Types of studies This review considered epidemiological study designs including randomized controlled trials, non-randomized controlled trials, quasi-experimental trials, prospective and retrospective cohort studies, case control studies and analytical cross-sectional studies. Types of outcomes This review considered studies that included (but were not limited to) the following mental disorder outcome measures: cognitive deficits and impairments, acquired language disorder, school performance and psychomotor skills. There are many tests to measure these outcomes. Cognitive deficits and impairments are commonly measured with the Mini-Cog Test, language disorders with the Language Delays Assessment Test and psychomotor skills are measured with the Two-point Threshold Test (distance perception) and the Color Timing Test that measures mental speed. School performance is not commonly measured with norm-referenced standardized tests due to the large disparities in achievement between schools. This outcome measure is often picked from class assessment and examination records of the students, relative to their classmates. Search strategy A three-step search strategy was utilized in this review. Relevant studies published in the English language from 1980 to 2012, when the association between malaria and mental disorders was highlighted, were considered for inclusion in this review. Unpublished data was also searched for within the same period. The databases searched included PubMed, CINAHL, PsycARTICLES, PsycBITES, PsycINFO, Social Science Citation Index, ProQuest Dissertations and Theses (PQDT)/Digital dissertations, ProQuest Social Services abstracts, ProQuest Sociological abstracts, World Bank, British Library for Development Studies, SCOPUS and Mednar. Methodological quality Quantitative papers selected for retrieval were assessed by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute (i.e. JBI-MAStARI). Any disagreements that arose between the reviewers were resolved through discussion. Data collection Data were extracted from quantitative papers included in the review using the standardized data extraction tool from JBI-MAStARI. The data extracted included specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. Data synthesis Meta-analysis was not done because the nature of the results from included studies did not make it statistically prudent to pool the results. Results A total of eight studies which met the inclusion criteria for this review were identified. Four (50%) studies were conducted in Kenya, three (37.5%) from Uganda and one (12.5%) from Senegal. The results of the review suggested that P. falciparum malaria was associated with mental disorders. Conclusions The review suggested that P. falciparum malaria is associated with mental disorders. However, there should be collaboration between investigators in this area so that multi-center trials can be conducted to ascertain the effects of P. falciparum malaria on more focused mental disorder outcomes.

Tactile Acuity Charts: A Reliable Measure of Spatial Acuity

For assessing tactile spatial resolution it has recently been recommended to use tactile acuity charts which follow the design principles of the Snellen letter charts for visual acuity and involve active touch. However, it is currently unknown whether acuity thresholds obtained with this newly developed psychophysical procedure are in accordance with established measures of tactile acuity that involve passive contact with fixed duration and control of contact force. Here we directly compared tactile acuity thresholds obtained with the acuity charts to traditional two-point and grating orientation thresholds in a group of young healthy adults. For this purpose, two types of charts, using either Braille-like dot patterns or embossed Landolt rings with different orientations, were adapted from previous studies. Measurements with the two types of charts were equivalent, but generally more reliable with the dot pattern chart. A comparison with the two-point and grating orientation task data showed that the test-retest reliability of the acuity chart measurements after one week was superior to that of the passive methods. Individual thresholds obtained with the acuity charts agreed reasonably with the grating orientation threshold, but less so with the two-point threshold that yielded relatively distinct acuity estimates compared to the other methods. This potentially considerable amount of mismatch between different measures of tactile acuity suggests that tactile spatial resolution is a complex entity that should ideally be measured with different methods in parallel. The simple test procedure and high reliability of the acuity charts makes them a promising complement and alternative to the traditional two-point and grating orientation thresholds.

Two-Point Orientation Discrimination Versus the Traditional Two-Point Test for Tactile Spatial Acuity Assessment

Two-point discrimination is widely used to measure tactile spatial acuity. The validity of the two-point threshold as a spatial acuity measure rests on the assumption that two points can be distinguished from one only when the two points are sufficiently separated to evoke spatially distinguishable foci of neural activity. However, some previous research has challenged this view, suggesting instead that two-point task performance benefits from an unintended non-spatial cue, allowing spuriously good performance at small tip separations. We compared the traditional two-point task to an equally convenient alternative task in which participants attempt to discern the orientation (vertical or horizontal) of two points of contact. We used precision digital readout calipers to administer two-interval forced-choice versions of both tasks to 24 neurologically healthy adults, on the fingertip, finger base, palm, and forearm. We used Bayesian adaptive testing to estimate the participants’ psychometric functions on the two tasks. Traditional two-point performance remained significantly above chance levels even at zero point separation. In contrast, two-point orientation discrimination approached chance as point separation approached zero, as expected for a valid measure of tactile spatial acuity. Traditional two-point performance was so inflated at small point separations that 75%-correct thresholds could be determined on all tested sites for fewer than half of participants. The 95%-correct thresholds on the two tasks were similar, and correlated with receptive field spacing. In keeping with previous critiques, we conclude that the traditional two-point task provides an unintended non-spatial cue, resulting in spuriously good performance at small spatial separations. Unlike two-point discrimination, two-point orientation discrimination rigorously measures tactile spatial acuity. We recommend the use of two-point orientation discrimination for neurological assessment.

Laterality and sex differences in tactile detection and two-point thresholds modified by body surface area and body fat ratio

Tactile detection and two-point discrimination tests are commonly used in neurological examinations. However, questions remain about the influence of both body and patient characteristics on test thresholds. The left side of the body has sometimes been reported more tactilely sensitive than the right, and females are said to be more sensitive than males. We measured tactile detection and two-point discrimination thresholds on the finger, palm, and forehead of a large sample of young adults (N = 171), examining laterality and sex differences, and the effects of body surface area (BSA) and body fat ratio (BFR). In tactile detection, there were no effects of laterality, BSA, or BFR, although females had lower thresholds than males. In two-point discrimination, there was an effect of laterality, with lower thresholds on the left side. This probably reflects hemispheric spatial processing differences. A significant BFR effect implies that subcutaneous fat affects skin deformation, but there were no effects of sex or BSA. The two-point discrimination findings differ in several respects from recent findings using grating orientation discriminations. A small positive correlation between the tasks, falling far short of test–retest reliabilities, indicates that they use largely disjoint but partially overlapping processes.

Perception of electrical and mechanical stimulation of the skin: implications for electrotactile feedback

Spinal cord injury is often accompanied by impaired tactile and proprioceptive sensations. Normally, somatosensensory information derived from such sensations is important in the formation of voluntary motor commands. Therefore, as a preliminary step toward the development of an electrotactile feedback system to restore somatosensation, psychophysical methods were used to characterize perceptual attributes associated with electrical stimulation of the skin on the back of the neck in human subjects. These data were compared to mechanical stimulation of the skin on the back of neck and on the distal pad of the index finger. Spatial acuity of the neck, evaluated using two-point thresholds, was not significantly different for electrical (37 ± 14 mm) or mechanical stimulation (39 ± 10 mm). The exponent (β) of the best fitting power function relating perceived intensity to applied stimulus strength was used to characterize perceptual sensitivity to mechanical and electrical stimuli. For electrical stimuli, both current amplitude-modulated and frequency-modulated trains of pulses were tested. Perceptual sensitivity was significantly greater for current amplitude modulation (β = 1.14 ± 0.37) compared to frequency modulation (β = 0.57 ± 0.24) and mechanical stimulation (0.51 ± 0.12). Finally, based on the data gathered here, we derive a transfer function that could be used in the future to convert mechanical stimuli detected with artificial sensors placed on the fingers into electrotactile signals that evoke perceptions similar to those arising from normal mechanical stimulation of the skin.

Application of a modified two-point backward difference to sequential event detection in surface electromyography

Reliable detection of onset and termination of muscle contraction is an essential task in the analysis of surface electromyographic signals. An event detection method that can be used for sequential detection of both onset and termination of muscle contraction is described. The method builds on the techniques of envelope detection, two-point backward difference and threshold based decision making. Therefore, fast conventional digital signal processing techniques can be used in its implementation. Because the method is computationally efficient, it can be employed in both real-time and non-real-time applications. This text discusses the architecture of the method, considers the practical aspects of its implementation, analyses its computational complexity and evaluates its performance on the grounds of experimental results.

A quantitative method for determining spatial discriminative capacity

BackgroundThe traditional two-point discrimination (TPD) test, a widely used tactile spatial acuity measure, has been criticized as being imprecise because it is based on subjective criteria and involves a number of non-spatial cues. The results of a recent study showed that as two stimuli were delivered simultaneously, vibrotactile amplitude discrimination became worse when the two stimuli were positioned relatively close together and was significantly degraded when the probes were within a subject's two-point limen. The impairment of amplitude discrimination with decreasing inter-probe distance suggested that the metric of amplitude discrimination could possibly provide a means of objective and quantitative measurement of spatial discrimination capacity.MethodsA two alternative forced-choice (2AFC) tracking procedure was used to assess a subject's ability to discriminate the amplitude difference between two stimuli positioned at near-adjacent skin sites. Two 25 Hz flutter stimuli, identical except for a constant difference in amplitude, were delivered simultaneously to the hand dorsum. The stimuli were initially spaced 30 mm apart, and the inter-stimulus distance was modified on a trial-by-trial basis based on the subject's performance of discriminating the stimulus with higher intensity. The experiment was repeated via sequential, rather than simultaneous, delivery of the same vibrotactile stimuli.ResultsResults obtained from this study showed that the performance of the amplitude discrimination task was significantly degraded when the stimuli were delivered simultaneously and were near a subject's two-point limen. In contrast, subjects were able to correctly discriminate between the amplitudes of the two stimuli when they were sequentially delivered at all inter-probe distances (including those within the two-point limen), and improved when an adapting stimulus was delivered prior to simultaneously delivered stimuli.ConclusionSubjects' capacity to discriminate the amplitude difference between two vibrotactile stimulations was degraded as the inter-stimulus distance approached the limit of their two-point spatial discriminative capacity. This degradation of spatial discriminative capacity lessened when an adapting stimulus was used. Performance of the task, as well as improvement on the task with adaptation, would most likely be impaired if the cortical information processing capacity of a subject or subject population were systemically altered, and thus, the methods described could be effective measures for use in clinical or clinical research applications.