Tactile Acuity Research Articles

Association between psychological traits and occlusal tactile acuity of healthy individuals.

Tactile acuity is a somatosensory measure of the extent to which humans can discern tactile stimuli. It is influenced by how peripheral signals are processed centrally. In the oral cavity, Occlusal Tactile Acuity (OTA) is the ability to perceive minimal thicknesses between antagonist teeth. The aim of the current study was to assess the association between psychological traits and OTA of otherwise healthy individuals. Sixty-three volunteers (32 males; mean age ± SD: 24.6 ± 2.7 years) participated in this study. Somatosensory amplification, anxiety, depression, physical symptoms and pain catastrophizing were scored using questionnaires, and subgroups of severity were created per variable based on cut-offs. OTA was measured using 9 aluminium foils with thickness (ranging from 8 to 72 μm) and one sham test (without foil). Each thickness was tested 10 times in random order, the participants were instructed to report whether they felt the foil between their molars and the mean percentage of correct answers was computed. A linear mixed model was used with OTA as a dependent variable and psychological domain as an independent variable. Significantly different OTA was observed among the anxiety subgroups (p = .003), supporting a decreased perception of thicknesses 24 and 32 μm (p = .018 and p < .001, respectively) in participants with moderate/severe anxiety compared to those with no/mild anxiety. Significantly different OTA was also observed among the pain catastrophizing subgroups (p = .008), showing decreased perception of thicknesses 32 and 40 μm (p < .001 and p = .007, respectively) in severe catastrophizing levels, compared to no/mild catastrophizing levels. No significant differences were observed for the other variables. Healthy adults with increased anxiety or pain catastrophizing levels show decreased interdental acuity as compared to participants with minor or no psychological impairment.

Blind individuals' enhanced ability to sense their own heartbeat is related to the thickness of their occipital cortex.

Blindness is associated with heightened sensory abilities, such as improved hearing and tactile acuity. Moreover, recent evidence suggests that blind individuals are better than sighted individuals at perceiving their own heartbeat, suggesting enhanced interoceptive accuracy. Structural changes in the occipital cortex have been hypothesized as the basis of these behavioral enhancements. Indeed, several studies have shown that congenitally blind individuals have increased cortical thickness within occipital areas compared to sighted individuals, but how these structural differences relate to behavioral enhancements is unclear. This study investigated the relationship between cardiac interoceptive accuracy and cortical thickness in 23 congenitally blind individuals and 23 matched sighted controls. Our results show a significant positive correlation between performance in a heartbeat counting task and cortical thickness only in the blind group, indicating a connection between structural changes in occipital areas and blind individuals' enhanced ability to perceive heartbeats.

The relationship between sustained hamstring pain and reorganisation of somatosensory representations: a randomised, controlled study.

Recurrent hamstring injuries are highly prevalent amongst sporting populations. It has been hypothesised that pain from an initial hamstring injury may induce reorganisation of somatosensory representations that could contribute to reinjury. However, because of the cross-sectional nature of existing research, it remains unknown whether somatosensory changes are a cause or effect of pain or if they are driven by other potentially confounding factors. Here, we explored the effect of experimentally induced sustained hamstring pain on tasks that interrogate somatosensory and spatial representations. Fifty healthy participants were randomly allocated to an experimental group that performed an eccentric exercise protocol on the right hamstring to induce delayed onset muscle soreness or a control group performing a repetition-matched concentric exercise protocol. The tactile cortical representation was assessed using two-point discrimination and tactile localisation, whereas the proprioceptive representation was assessed using a left-right judgement task. Peripersonal spatial representations were assessed using an auditory localisation task. Assessments were performed at baseline and day 2. No between-group differences in tactile acuity were observed. However, improvements in left-right judgments and worsening of auditory localisation occurred in the experimental group compared with the control group. This study provides preliminary evidence showing that somatosensory changes occur in response to sustained hamstring pain. Experimentally induced, sustained hamstring pain elicited enhancements in proprioceptive processing and deficits in peripersonal spatial processing, suggesting a shift in the allocation of attentional resources from the external (peripersonal) to internal (body) environment. These findings may hold important implications for reinjury risk and rehabilitation following hamstring pain.

Theta-burst stimulation over primary somatosensory cortex modulates tactile acuity of tongue.

Emerging studies in humans have established the modulatory effects of repetitive transcranial magnetic stimulation (rTMS) over primary somatosensory cortex (S1) on somatosensory cortex activity and perception. However, to date, research in this area has primarily focused on the hand and fingers, leaving a gap in our understanding of the modulatory effects of rTMS on somatosensory perception of the orofacial system and speech articulators. The present study aimed to examine the effects of different types of theta-burst stimulation-continuous TBS (cTBS), intermittent TBS (iTBS), or sham-over the tongue representation of left S1 on tactile acuity of the tongue. In a repeated-measures design, fifteen volunteers participated in four separate sessions, where cTBS, iTBS, sham, or no stimulation was applied over the tongue representation of left S1. Effects of TBS were measured on both temporal and spatial perceptual acuity of tongue using a custom vibrotactile stimulator. CTBS significantly impaired spatial amplitude threshold at the time window of 16-30 minutes after stimulation, while iTBS improved it at the same time window. The effect of iTBS, however, was smaller than cTBS. In contrast, neither cTBS nor iTBS had any effect on the temporal discrimination threshold. The current study establishes the validity of using TBS to modulate somatosensory perception of the orofacial system. Directly modifying somatosensation in the orofacial system has the potential to benefit clinical populations with abnormal tactile acuity, improve our understanding of the role of sensory systems in speech production, and enhance speech motor learning and rehabilitation.

Sense of ownership influence on tactile perception: Is the predictive coding account valid for the somatic rubber hand Illusion?

According to the predictive coding account, the attenuation of tactile perception on the hand exposed to the visuo-tactile Rubber Hand Illusion (vtRHI) relies on a weight increase of visual information deriving from the fake hand and a weight decrease of tactile information deriving from the individual’s hand. To explore if this diametrical modulation persists in the absence of vision when adopting the somatic RHI (sRHI), we recorded tactile acuity measures before and after both RHI paradigms in 31 healthy individuals, hypothesizing a weight decrease for somatosensory information deriving from the hand undergoing the illusion and a weight increase for those deriving from the contralateral hand in the sRHI. Our results showed a significant overall decrease in tactile acuity on the hand undergoing the illusion whilst no changes emerged on the contralateral hand during sRHI. Since the sRHI was not accompanied by the hand spatial remapping, despite the generation of the feeling of ownership toward the fake hand, we hypothesized spatial remapping might play a pivotal role in determining sensory information weight attribution.

Two-Point Discrimination for Upper Extremity and Face in Healthy Young Adults: A Cross-Sectional Study

Background and Aim: The threshold values of two-point discrimination (TPD) provide a numerical measure of tactile acuity. Normal reference values are needed to decide whether sensory variability is within normal sensorial limits. The study aimed to determine the upper extremity and face threshold values in healthy young adults. Materials and Methods: Static TPD thresholds of 67 healthy young adults aged 18–35 years were assessed. Eight skin areas in the face and upper extremity on the dominant side were assessed using a “method of limits” approach with an aesthesiometer. Differences between genders were examined with the Mann–Whitney U test. The Spearman correlation analysis investigated the relationship between age and TPD measurements. Results: TPD values ranged between 4.66 and 19.16 mm and 1.33-68.66 mm in the face and upper extremity, respectively, in the participants with a mean age of 23.83 ± 4.66 years. Fingertips and the area over the lateral mandibula showed the greatest sensitivity. The threshold values of TPD showed both interindividual and intraindividual variability. There was no statistical difference in the TPD values according to gender in any of the measured areas, and there was no relationship between age and TPD test values. Conclusions: The threshold values of TPD have clinical applicability in various diseases affecting the sensation of the upper extremity and/or face. These data may help the detection of early sensory loss.

Pain symptoms are associated with two-point discrimination threshold in patients with temporomandibular disorders.

This study aimed to explore the associations of orofacial two-point discrimination (2-PD) test result with pain symptoms and psychological factors in patients with Temporomandibular Disorders (TMDs). 193 patients with TMDs were included in this study. Patients' demographics, pain intensity, and psychological status were recorded. The 2-PDs in the bilateral temporal, zygomatic, mandibular, and temporomandibular joint (TMJ) regions of the patients were measured. Statistical analyses were conducted to observe the associations between variables. For Pain-related TMDs (PT) patients, Monthly Visual Analogue Scale (VAS-M) and Current Analogue Scale (VAS-C) were correlated with TMJ, zygomatic and temporal 2-PDs. Patients with PT tended to have higher TMJ 2-PDs[Right: β = 1.827mm, 95%CI(0.107, 3.548), P = 0.038], zygomatic 2-PDs[Right: β = 1.696mm, 95%CI(0.344, 3.048), P = 0.014], temporal 2-PDs[Left: β = 2.138mm, 95%CI(0.127, 4.149), P = 0.037; Right: β = 1.893mm, 95%CI(0.011, 3.775), P = 0.049]. Associations were also observed between VAS-C and TMJ 2-PDs[Left: β = 0.780, 95%CI(0.190, 1.370), P = 0.01; Right: β = 0.885, 95%CI(0.406, 1.364), P = 0.001], Zygomatic 2-PDs[Right: β = 0.555, 95%CI(0.172, 0.938), P = 0.005]; VAS-M and TMJ 2-PDs[Left: β = 0.812, 95%CI(0.313, 1.311), P = 0.002; Right: β = 0.567, 95%CI(0.152, 0.983), P = 0.008], zygomatic 2-PDs[Left: β = 0.405, 95%CI(0.075, 0.735), P = 0.016; Right: β = 0.545, 95%CI(0.221, 0.870), P = 0.001], and temporal 2-PDs [Left: β = 0.741, 95%CI(0.258, 1.224), P = 0.003; Right: β = 0.519, 95%CI(0.063, 0.975), P = 0.026]. TMJ, zygomatic, and temporal 2-PDs were significantly associated with PT and pain intensity. Age, gender and psychological factors were not associated with orofacial 2-PDs. PT patients exhibited weaker tactile acuity compared to Non-PT patients. Further discussion on the underlying mechanism is needed. Orofacial tactile acuity of TMDs patients was associated with their pain symptoms, which researchers should take account into when performing 2-PD tests for TMDs patients. The 2-PD test can be considered as a potential tool along with the current procedures for the differentiations of PT and Non-PT.

Prospective comparative study on enhancing geometrical mental representation and anatomical learning in medical students through modeling clay as an assessment tool.

While traditional anatomy education often emphasizes passive learning and rote memorization, it seldom employs constructivist theories that focus on active, hands-on experiences for effective learning. This study tests the hypothesis that tactile experiences with modeling clay enhance geometric mental representation more effectively than verbal descriptions. We examine the potential of clay modeling to reflect and evaluate students' mental representation of anatomical structures. Utilizing a prospective randomized, open, blind endpoint (PROBE) design, we engaged 36 participants divided into three groups: blind, visually impaired, and a control group. The primary outcome measure was the difference between post-touch score and pre-touch score, which gauged the efficacy of tactile intervention in enhancing the participants' capacity to mentally reconstruct a well-designed anatomical fiction structure. Scoring was executed using a double-blind double-evaluation methodology, positioning clay model reconstruction as both an objective reliable assessment and a pedagogical tool. The analysis demonstrated a pronounced improvement in mental representation of anatomical structures, particularly in spatial comprehension and detailed textural discernment, with the mean score soaring from 47.81 pre-touch to 85.09 post-touch. Distinct cognitive processing adaptations were evident across groups, with the blind group excelling in tactile acuity and the visually impaired group showing the most significant gains in spatial understanding post-intervention (Cohen's d = 2.74). The application of modeling clay as a tactile intervention tool can significantly improve the learning of anatomy among medical students. The study underscores the value of active, multisensory engagement and customized teaching strategies for effective anatomy education among this demographic.

Toe stimulation improves tactile perception of the genitals.

The human body is represented in a topographic pattern in the primary somatosensory cortex (S1), and genital representation is displaced below the toe representation. However, the relationship between the representation of the genitals and toe in S1 remains unclear. In this study, tactile stimulation was applied to the big toe in healthy subjects to observe changes in tactile acuity in the unstimulated genital area, abdomen, and metacarpal dorsal. Then tactile stimulation was applied to the right abdomen and metacarpal dorsal to observe changes in tactile acuity in bilateral genitals. The results revealed that tactile stimulation of the big toe led to a reduction in the 2-point discrimination threshold (2PDT) not only in the stimulated big toe but also in the bilateral unstimulated genitals, whereas the bilateral abdomen and metacarpal dorsal threshold remained unchanged. On the other hand, tactile stimulation of the abdomen and metacarpal dorsal did not elicit 2-point discrimination threshold changes in the bilateral genitals. Cortical and subcortical mechanisms have been proposed to account for the findings. One explanation involves the intracortical interaction between 2 adjacent representations. Another possible explanation is that the information content of a specific body part is broadly distributed across the S1. Moreover, exploring the links between human behaviors and changes in the cerebral cortex is of significant importance.

Hearing Aid Amplification Improves Postural Control for Older Adults With Hearing Loss When Other Sensory Cues Are Impoverished.

Recent studies suggest that sound amplification via hearing aids can improve postural control in adults with hearing impairments. Unfortunately, only a few studies used well-defined posturography measures to assess balance in adults with hearing loss with and without their hearing aids. Of these, only two examined postural control specifically in the elderly with hearing loss. The present study examined the impact of hearing aid use on postural control during various sensory perturbations in older adults with age-related hearing loss. Thirty individuals with age-related hearing impairments and using hearing aids bilaterally were tested. Participants were asked to perform a modified clinical sensory integration in balance test on a force platform with and without hearing aids. The experiment was conducted in the presence of a broadband noise ranging from 0.1 to 4 kHz presented through a loudspeaker. As expected, hearing aid use had a beneficial impact on postural control, but only when visual and somatosensory inputs were both reduced. Data also suggest that hearing aid use decreases the dependence on somatosensory input for maintaining postural control. This finding can be of particular importance in older adults considering the reduction of tactile and proprioceptive sensitivity and acuity often associated with aging. These results provide an additional argument for encouraging early hearing aid fitting for people with hearing loss.

Are blind individuals immune to bodily illusions? Somatic rubber hand illusion in the blind revisited

Multisensory awareness of one’s own body relies on the integration of signals from various sensory modalities such as vision, touch, and proprioception. But how do blind individuals perceive their bodies without visual cues, and does the brain of a blind person integrate bodily senses differently from a sighted person? To address this question, we aimed to replicate the only two previous studies on this topic, which claimed that blind individuals do not experience the somatic rubber hand illusion, a bodily illusion triggered by the integration of correlated tactile and proprioceptive signals from the two hands. We used a larger sample size than the previous studies and added Bayesian analyses to examine statistical evidence in favor of the lack of an illusion effect. Moreover, we employed tests to investigate whether enhanced tactile acuity and cardiac interoceptive accuracy in blind individuals could also explain the weaker illusion. We tested 36 blind individuals and 36 age- and sex-matched sighted volunteers. The results show that blind individuals do not experience the somatic rubber hand illusion based on questionnaire ratings and behavioral measures that assessed changes in hand position sense toward the location of the rubber hand. This conclusion is supported by Bayesian evidence in favor of the null hypothesis. The findings confirm that blind individuals do not experience the somatic rubber hand illusion, indicating that lack of visual experience leads to permanent changes in multisensory bodily perception. In summary, our study suggests that changes in multisensory integration of tactile and proprioceptive signals may explain why blind individuals are “immune” to the nonvisual version of the rubber hand illusion.

A single session of action observation therapy versus observing a natural landscape in adults with chronic neck pain – a randomized controlled trial

BackgroundAction observation (AO) has emerged as a potential neurorehabilitation therapy for patients with neck pain (NP), but evidence of its effectiveness is scarce. This study aims to assess the effect of a single session of AO when compared to observing a natural landscape on NP intensity, fear of movement, fear-avoidance beliefs, neck muscles’ strength, pressure pain threshold, and tactile acuity.MethodsSixty participants with NP were randomly allocated to the AO group (n = 30) or control group (n = 30). Both groups watched an 11-minute video: the AO group watched a video of a person matched for age and sex performing neck exercises, while the control group watched a video of natural landscapes. Neck pain intensity, fear of movement, fear-avoidance beliefs, tactile acuity, pressure pain thresholds, and neck muscle strength were assessed both at baseline and post-intervention. General linear models of repeated measures (ANCOVA of two factors) were used to explore between-group differences at post-intervention.ResultsThere was a significant main effect of time for pain intensity (p = 0.02; η2p = 0.09; within-group mean change and 95% CI: AO=-1.44 (-2.28, -0.59); control=-1.90 (-2.74, -1.06), but no time versus group interaction (p = 0.46). A time versus group significant interaction was found for one out of the six measurement sites of two-point discrimination and the neck flexors strength (p < 0.05) favoring the control group. No other statistically significant differences were found for the remaining variables).ConclusionsResults suggest a similar acute benefit for both a single session of AO and observing natural landscapes for promoting hypoalgesia, but no impact on kinesiophobia, fear-avoidance beliefs, or pressure pain thresholds. Also, AO had no positive effect on two-point discrimination and muscle strength. Further research is needed, with longer interventions.Trial registrationClinialtrials.gov (NCT05078489).

Occlusal tactile acuity in patients with burning mouth syndrome: A case-control study

ObjectivesOcclusal Tactile Acuity (OTA) is the ability to detect small thicknesses between occluding teeth. Individuals diagnosed with Burning Mouth Syndrome (BMS) often refer an uncomfortable sensation associated with their occlusion. The aim of the current study was to measure the OTA in BMS patients, and to compare it with that of age and gender matched pain free controls. Materials and methods25 BMS patients and 25 controls were enrolled. The OTA was tested with 10 different thicknesses: 9 aluminium foils (8 –72 µm with a constant increment of 8 µm) and 1 sham test (without foil), each thickness being tested 10 times in random order (100 tests in total). ResultsSignificantly increased OTA was observed in the BMS group, compared to the controls group, for the foil thicknesses between 8 µm and 48 µm. Furthermore, BMS patients showed substantial impairment in the detection of the sham test, even if this finding did not reach statistically significance (P = 0.743). ConclusionsBMS patients presented increased ability to detect small thicknesses between antagonist teeth during intercuspation. These findings might explain the high somatosensory distortion referred by those patients, in absence of objective clinical findings.

Development and validation of child’s food texture preference questionnaire and associations with oral tactile sensitivity and food fussiness in children

This study aimed to 1) develop a parent-reported child’s food texture preference questionnaire, 2) assess content validity and inter-rater reliability among parent-, child-report and the child report after tasting and 3) validate the questionnaire with oral tactile acuity and food fussiness in 5 to 12-year-old Australian children. Parents rated their child’s preference for 29 pairs of foods selected as they were different in texture but similar in other sensory attributes. A subset of these food pairs (10 pairs) was used for child reported preference and preference after tasting (4 pairs). Content validity was rated by 7 experts and expressed as the content validation index for items. Grating orientation task was used to measure oral tactile sensitivity. Parents reported fussiness on the Children’s Eating Behavior Questionnaire fussiness subscale. A total of 154 caregivers and 251 children (129 boys, 122 girls) participated. Content validation resulted in the elimination of 9 items. Child-rated texture preference was positively correlated with preference after tasting (r = 0.55) and parent-reported scores (r = 0.31). A moderate positive correlation was found between preference after tasting and parent reported scores (r = 0.20). Child's food texture preference was positively associated with child’s age (p < 0.05) but not correlated with measured oral tactile sensitivity or food fussiness. This is the first study to evaluate content validity and inter-rater reliability of parent-report child’s food texture preference measure. There still remains opportunities for improvements of both food texture preference measure and oral tactile sensitivity.

Quantifying spatial acuity of frequency resolved midair ultrasound vibrotactile stimuli

Spatial acuity is a fundamental property of any sensory system. In the case of the somatosensory system, the two-point discrimination (2PD) test has long been used to investigate tactile spatial resolution. However, the somatosensory system comprises three main mechanoreceptive channels: the slowly adapting channel (SA) responds to steady pressure, the rapidly adapting channel (RA) responds to low-frequency vibration, and the Pacinian channel (PC) responds to high-frequency vibration. The use of mechanical stimuli in the classical 2PD test means that previous studies on tactile acuity have primarily focussed on the pressure-sensitive channel alone, while neglecting other submodalities. Here, we used a novel ultrasound stimulation to systematically investigate the spatial resolution of the two main vibrotactile channels. Contrary to the textbook view of poor spatial resolution for PC-like stimuli, across four experiments we found that high-frequency vibration produced surprisingly good spatial acuity. This effect remained after controlling for interchannel differences in stimulus detectability and perceived intensity. Laser doppler vibrometry experiments confirmed that the acuity of the PC channel was not simply an artifact of the skin’s resonance to high-frequency mechanical stimulation. Thus, PC receptors may transmit substantial spatial information, despite their sparse distribution, deep location, and large receptive fields.

Sensory Reweighting for Postural Control in Older Adults with Age-Related Hearing Loss.

There is growing evidence linking hearing impairments and the deterioration of postural stability in older adults. To our knowledge, however, no study to date has investigated the effect of age-related hearing loss on the sensory reweighting process during postural control. In the absence of data, much is unknown about the possible mechanisms, both deleterious and compensatory, that could underly the deterioration of postural control following hearing loss in the elderly. The aim of this study was to empirically examine sensory reweighting for postural control in older adults with age-related hearing loss as compared to older adults with normal hearing. The center of pressure of all participants was recorded using a force platform and the modified clinical test of sensory interaction and balance protocol. The results suggest that individuals with age-related hearing loss displayed increased somatosensory reliance relative to normal hearing younger adults. This increased reliance on somatosensory input does not appear to be effective in mitigating the loss of postural control, probably due to the concomitant deterioration of tactile and proprioceptive sensitivity and acuity associated with aging. Beyond helping to further define the role of auditory perception in postural control, these results further the understanding of sensory-related mechanisms associated with postural instability in older adults.

Inter- and Intra-Examiner Reliability Study of Two-Point Discrimination Test (TPD) and Two-Point Estimation Task (TPE) in the Sacral Area of Pain-Free Individuals.

Tactile acuity is typically measured by a two-point discrimination test (TPD) and a two-point estimation task (TPE). In the back area, they are only conducted in the lumbar and cervical regions of the spine. Considering that such measurements have not been conducted in the sacral regions, the purpose of this study was to assess the inter- and intra-examiner reliability of the TPD and TPE at the level of the S3 segment. The study included 30 pain-free subjects aged 20-30 years. Tests were performed with a pair of stainless hardened digital calipers. The TPD was measured in two locations: 5 and 15 cm from the midline; for TPE both, points were located inside the measured area. Session 1 involved assessments by two examiners in 10-min intervals. Session 2 was measured by one examiner, at analogous intervals between tests. The TPD inter-rater reliability was excellent for mean measurements (ICC3.2: 0.76-0.8; ICC3.3: 0.8-0.92); the intra-rater reliability was excellent for mean measurements (ICC2.2: 0.79-0.85; ICC2.3: 0.82-0.86). The TPE inter-rater reliability was good to excellent for mean measurements (ICC3.2: 0.65-0.92; ICC3.3: 0.73-0.94); the intra-rater reliability for all studies (ICC2.1, ICC2.2, ICC2.3) was excellent (0.85-0.89). Two measurements are sufficient to achieve good reliability (ICC ≥ 0.75), regardless of the assessed body side.

An individual's skin stiffness predicts their tactile discrimination of compliance.

Individual differences in tactile acuity have been correlated with age, gender and finger size, whereas the role of the skin's stiffness has been underexplored. Using an approach to image the 3-D deformation of the skin surface during contact with transparent elastic objects, we evaluate a cohort of 40 young participants, who present a diverse range of finger size, skin stiffness and fingerprint ridge breadth. The results indicate that skin stiffness generally correlates with finger size, although individuals with relatively softer skin can better discriminate compliant objects. Analysis of contact at the skin surface reveals that softer skin generates more prominent patterns of deformation, in particular greater rates of change in contact area, which correlate with higher rates of perceptual discrimination of compliance, regardless of finger size. Moreover, upon applying hyaluronic acid to soften individuals' skin, we observe immediate, marked and systematic changes in skin deformation and consequent improvements in perceptual acuity in differentiating compliance. Together, the combination of 3-D imaging of the skin surface, biomechanics measurements, multivariate regression and clustering, and psychophysical experiments show that subtle distinctions in skin stiffness modulate the mechanical signalling of touch and shape individual differences in perceptual acuity. KEY POINTS: Although declines in tactile acuity with ageing are a function of multiple factors, for younger people, the current working hypothesis has been that smaller fingers are better at informing perceptual discrimination because of a higher density of neural afferents. To decouple relative impacts on tactile acuity of skin properties of finger size, skin stiffness, and fingerprint ridge breadth, we combined 3-D imaging of skin surface deformation, biomechanical measurements, multivariate regression and clustering, and psychophysics. The results indicate that skin stiffness generally correlates with finger size, although it more robustly correlates with and predicts an individual's perceptual acuity. In particular, more elastic skin generates higher rates of deformation, which correlate with perceptual discrimination, shown most dramatically by softening each participant's skin with hyaluronic acid. In refining the current working hypothesis, we show the skin's stiffness strongly shapes the signalling of touch and modulates individual differences in perceptual acuity.

Oral acuity, particle size sensitivity, and food texture preferences in an older adult population

Changes in sensory sensitivity occur as we age but changes in food texture sensitivity in the older adult population remain poorly understood. The objective of this study was to describe the relationship between oral tactile acuity, mouth behaviour, and particle size sensitivity and their potential influence on preferred food textures in older adults. Older adults (n = 79; mean age = 69.7 yrs) participated in an evaluation of oral health and texture perception through survey measurements of mouth behaviour, and preferred food textures. Oral tactile acuity was assessed using the Grating Orientation Task (GOT) with three grating sizes (0.5, 0.75, and 1.5 mm). Food particle sensitivity was evaluated through a difference-from-control (DFC) sensory assessment of ground quinoa mixed into yogurt, utilizing three particle size ranges (<75, 150–250, and 500–600 μm). The results revealed that the sample containing 500–600 mm particle sizes yielded a higher difference (DFC) score compared to the samples with < 75 μm and 150–250 μm particles (p < 0.05). However, no significant relationship (p > 0.05) was found between the R-indices obtained from the GOT assessments and DFC scores, indicating no association between oral tactile acuity and particle size sensitivity. Liking ofcreamy, leafy, slippery, sticky, with skins,andcombinationfood textures was significantly positively associated with the 0.5 mm GOT tool R-index values, suggesting higher oral acuity influences liking of specific food textures. Significant differences (p < 0.05) were present in liking of food textures among different mouth behaviour groups. These results suggest that texture perception and sensitivity influence texture acceptance in older adults.

Tactile acuity improves during acute experimental pain of the limb.

Chronic pain is associated with poor tactile acuity, commonly measured with the 2-point discrimination (TPD) test. Although poor tactile acuity across chronic pain conditions is well established, less is known in acute pain. Recent conflicting findings in experimentally induced neck and back pain led us to conduct a TPD investigation in experimentally induced limb pain. We hypothesised altered TPD during experimental upper limb pain, but we did not speculate on the direction of the change. Thirty healthy subjects immersed their dominant hand in a circulating cold-water bath at 7°C (cold pressor test [CPT]). Two-point discrimination was measured at baseline (pre-CPT), during pain (during-CPT), and after withdrawal from the water (post-CPT) in 3 different sites: (1) the dominant forearm, (2) dominant arm and (3) contralateral forearm. Repeated-measures analysis of variance revealed a significant main effect of time (F(2,56) = 4.45, P = 0.02, = 0.14) on TPD; in all 3 sites, TPD values decreased (ie, tactile acuity improved) during pain. Interestingly, the contralateral forearm followed a similar pattern to the dominant (ie, painful) forearm, and furthermore was the only site that exhibited any correlation with pain, albeit in an intriguing direction (r = 0.57, P = 0.001), ie, the greater the pain the worse the tactile acuity. The improvements in tactile acuity during experimentally induced limb pain may reflect a protective response. The changes in the corresponding site in the contralateral limb may reflect a protective spinal cross talk. Such a response, together with the interesting relationship between tactile acuity and pain, warrant further inquiry.