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At least 19 recordsLinked to original sources
PubMed2003

Tactile acuity is enhanced in blindness.

Functional imaging studies in blind subjects have shown tactile activation of cortical areas that normally subserve vision, but whether blind people have enhanced tactile acuity has long been controversial. We compared the passive tactile acuity of blind and sighted subjects on a fully automated grating orientation task and used multivariate Bayesian data analysis to determine predictors of acuity. Acuity was significantly superior in blind subjects, independently of the degree of childhood vision, light perception level, or Braille reading. Acuity was strongly dependent on the force of contact between the stimulus surface and the skin, declined with subject age, and was better in women than in men. Despite large intragroup variability, the difference between blind and sighted subjects was highly significant: the average blind subject had the acuity of an average sighted subject of the same gender but 23 years younger. The results suggest that crossmodal plasticity may underlie tactile acuity enhancement in blindness.

Adult↗
PubMed1997

Association between a quantitative measure of tactile acuity and hand symptoms reported by operators of power tools.

An association between a quantitative measure of tactile acuity at the fingertips and symptoms of reduced manipulative function, as established by responses to a questionnaire, was demonstrated in a population of 81 manual workers from the mining industry (62 power-tool operators and 19 nonusers). Mechanoreceptor-specific vibrotactile thresholds were determined for the slowly adapting type I (SAI) and fast-adapting types I and II (FAI and FAII) receptors at the fingertip of the third digit of each hand. Statistically significant threshold shifts in SAI and/or FAII acuity were found in persons responding affirmatively to questions concerning finger/hand numbness, blanching, and difficulty buttoning clothing. The best predictors of a quantitative change in tactile acuity were questions relating to difficulty manipulating small objects and buttoning clothing, yielding positive predictive values of from 90% to 100% and false positive rates of from 0% to 2.8%. The demonstration of an association between a quantitative measure of tactile acuity at the fingertips and some symptom reports, obtained by means of a questionnaire, provides the basis for the development of a screening procedure for persons at risk of such disturbances in hand function.

Adult↗
PubMed2003

Decline of tactile acuity in aging: a study of body site, blood flow, and lifetime habits of smoking and physical activity.

Tactile acuity of 60 older subjects (> or = 65 years) and 19 younger subjects (18-28 years) was assessed by two-point gap thresholds at the upper and lower surfaces of the forefinger, at the upper and lower surfaces of the feet, and at the volar surface of the forearm. The older subjects were assigned to one of four groups of 15 subjects each, depending on reported lifetime habits of physical activity and smoking: (1) active smokers, (2) active nonsmokers, (3) inactive smokers, and (4) inactive nonsmokers. Peripheral blood flow was assessed at the forefinger, foot, and forearm by means of laser-Doppler imaging and skin temperature recordings, under resting conditions and during and after a 5-min exposure to mild cooling (28 degrees C). Consistent with previous studies, tactile acuity thresholds in the foot and finger averaged about 80% higher in the older subjects than in the younger subjects, but only about 22% higher in the forearm. Although the upper surface of the fingertip was more sensitive than the lower surface in both younger and older subjects, the age-related decline in tactile acuity was nearly identical on both sides of the finger and foot. The latter finding refutes the hypothesis that the larger effect of aging in the extremities results from greater physical wear and tear on the contact surfaces of the hands and feet. Self-reported lifetime histories of physical activity and smoking were not significantly associated with measures of cutaneous blood flow or tactile thresholds. Possible reasons for this lack of association are discussed, including the inherent limitations of testing only healthy older subjects, and the concept of "successful aging".

Adolescent↗
PubMed2006

Slanted joint axes of the stick insect antenna: an adaptation to tactile acuity.

Like many flightless, obligatory walking insects, the stick insect Carausius morosus makes intensive use of active antennal movements for tactile near range exploration and orientation. The antennal joints of C. morosus have a peculiar oblique and non-orthogonal joint axis arrangement. Moreover, this arrangement is known to differ from that in crickets (Ensifera), locusts (Caelifera) and cockroaches (Blattodea), all of which have an orthogonal joint axis arrangement. Our hypothesis was that the situation found in C. morosus represents an important evolutionary trait of the order of stick and leaf insects (Phasmatodea). If this was true, it should be common to other species of the Phasmatodea. The objective of this comparative study was to resolve this question. We have measured the joint axis orientation of the head-scape and scape-pedicel joints along with other parameters that affect the tactile efficiency of the antenna. The obtained result was a complete kinematic description of the antenna. This was used to determine the size and location of kinematic out-of-reach zones, which are indicators of tactile acuity. We show that the oblique and non-orthogonal arrangement is common to eight species from six sub-families indicating that it is a synapomorphic character of the Euphasmatodea. This character can improve tactile acuity compared to the situation in crickets, locusts and cockroaches. Finally, because molecular data of a recent study indicate that the Phasmatodea may have evolved as flightless, obligatory walkers, we argue that the antennal joint axis arrangement of the Euphasmatodea reflects an evolutionary adaptation to tactile near range exploration during terrestrial locomotion.

Animals↗
PubMed1992

The relationship of visual acuity, tactile sensitivity, and mobility of the upper extremities to proficient breast self-examination in women 65 and older.

The purpose of this study was to describe the relationship of visual acuity, tactile sensitivity, and mobility of the upper extremities to the performance of proficient breast self-examination (BSE) in women 65 and older. A convenience sample of 32 women, ages 66-89, met with the investigator to have their visual acuity, tactile sensitivity, and upper extremity mobility tested. Their ability to perform the visual, tactile, and upper extremity components of proficient BSE also was tested by using simulated breast models (SBMs). Thirty of the women had adequate visual acuity (< or = 20/40 Snellen equivalent) but were unable to visually detect the abnormalities on the SBM. Thirty of the women had tactile sensitivity of 10 mm (1 cm) or better on the static two-point discrimination test of the second, third, and fourth digits of each hand. Yet, only 13 of these women were able to locate the 1 cm lump; only 12 were able to locate the 5 mm lumps; and none were able to locate the 3 mm lump. The subjects' ability to pass the upper extremity mobility component of proficient BSE was significantly related to their ability to pass the upper extremity range of motion criteria. Limitations and deficits, mostly of the hands and shoulders, were revealed. When teaching BSE to older women, nurses are responsible for assessing limitations and deficits in their ability to perform proficient BSE and, if necessary, for intervening with alternatives. The need for further research in this area is indicated to improve assessment and education of older women regarding the use of proficient BSE for early detection of breast cancer.

Age Factors↗
PubMed1998

Factors affecting tactile spatial acuity.

Tactile spatial acuity on the fingerpad was measured using a grating orientation task. In this task, subjects are required to identify the orientation of square-wave gratings placed on the skin. Previous studies have shown that performance varies as a function of the width of the grooves in the gratings. In the present study, both groove width and the overall size and configuration of the contactors were varied. Sensitivity improved with wider grooves and with larger contactors. Additional measurements showed that the improved sensitivity is not the result of the increase in total area contacted, but rather is due to two other factors associated with larger contactors. One is the greater linear extent of the larger contactors. The other appears to be due to the reduction in the interference produced by the outer edge of the contactor. Specifically, as the contactor increases in size, the distance between the outer edge and the center portion of the grooves also increases. It was also shown that subjects are more sensitive to a single, continuous groove as compared with two grooves of the same total length but spatially discontinuous. Similarly, subjects are more sensitive to a contactor with a continuous groove than to a contactor in which just the end points of the groove are presented. The results are generally consistent with the results of peripheral, neurophysiological recordings. The results are discussed in terms of the way in which both spatial and intensive factors may affect sensitivity to grating orientation.

Analysis of Variance↗
PubMed2004

From innervation density to tactile acuity: 1. Spatial representation.

We tested the hypothesis that the population receptive field representation (a superposition of the excitatory receptive field areas of cells responding to a tactile stimulus) provides spatial information sufficient to mediate one measure of static tactile acuity. In psychophysical tests, two-point discrimination thresholds on the hindlimbs of adult cats varied as a function of stimulus location and orientation, as they do in humans. A statistical model of the excitatory low threshold mechanoreceptive fields of spinocervical, postsynaptic dorsal column and spinothalamic tract neurons was used to simulate the population receptive field representations in this neural population of the one- and two-point stimuli used in the psychophysical experiments. The simulated and observed thresholds were highly correlated. Simulated and observed thresholds' relations to physiological and anatomical variables such as stimulus location and orientation, receptive field size and shape, map scale, and innervation density were strikingly similar. Simulated and observed threshold variations with receptive field size and map scale obeyed simple relationships predicted by the signal detection model, and were statistically indistinguishable from each other. The population receptive field representation therefore contains information sufficient for this discrimination.

Animals↗
PubMed2003

Lingual tactile acuity, taste perception, and the density and diameter of fungiform papillae in female subjects.

A growing body of evidence suggests that individuals who differ in taste perception differ in lingual tactile perception. To address this issue, spatial resolution acuity was estimated for 83 young adult females (52 Asians and 31 Caucasians) by their ability to examine with the tongue and identify embossed letters of the alphabet. Ratings of the magnitude of the bitterness of 0.0032M 6-n-propylthiouracil (PROP) were obtained to characterize subjects' taste perception. The density and diameter of fungiform papillae on the anterior tongues of the Asian subjects were measured also. Subjects who rated the bitterness of PROP as very or intensely strong (supertasters) were found to be about 25% more tactually acute than subjects who rated the bitterness as moderate to strong (medium tasters) and twice as acute as subjects who rated it as nondetectable or weak (non-tasters; P<.0001): The threshold heights for letter recognition averaged 2.8, 3.5 and 5.4 mm, respectively, for the Asian subjects and 2.6, 3.2, and 5.1 mm for the Caucasian subjects. The thresholds correlated highly with subjects' ratings of bitterness (rho=-0.84, P<.0001), and for the Asian subjects with the density (rho=-0.84, P<.0001) and diameter (rho=0.66, P<.0001) of fungiform papillae. Mean densities varied from 54.4 cm(-2) (non-tasters) to 106.5 cm(-2) (medium tasters) to 143.7 cm(-2) (supertasters; P<.0001). These findings confirm that individuals who differ in taste (PROP) sensitivity also differ in lingual tactile acuity. Tactile and taste sensitivities covary and reflect individual differences in the density and diameter of fungiform papillae on the anterior tongue.

Adolescent↗
PubMed2001

Human locognosic acuity on the arm varies with explicit and implicit manipulations of attention: implications for interpreting elevated tactile acuity on an amputation stump.

In Experiment 1, normal subjects' ability to localize tactile stimuli (locognosia) delivered to the upper arm was significantly higher when they were instructed explicitly to direct their attention selectively to that segment than when they were instructed explicitly to distribute their attention across the whole arm. This elevation of acuity was eliminated when subjects' attentional resources were divided by superimposition of an effortful, secondary task during stimulation. In Experiment 2, in the absence of explicit attentional instruction, subjects' locognosic acuity on one of three arm segments was significantly higher when stimulation of that segment was 2.5 times more probable than that of stimulation of the other two segments. We surmise that the attentional mechanisms responsible for such modulations of locognosic acuity in normal subjects may contribute to the elevated sensory acuity observed on the stumps of amputees.

Adolescent↗
PubMed2005

From innervation density to tactile acuity 2: embryonic and adult pre- and postsynaptic somatotopy in the dorsal horn.

We tested the hypothesis that dorsal horn laminae III-IV cell receptive fields (RFs) are initially established in three steps: cutaneous axons penetrate the dorsal horn near their rostrocaudal (RC) levels of entry into the spinal cord. Their terminal branches distribute mediolaterally (ML) according to their relative distoproximal RF locations on the leg, and form nonselective synapses with nearby dorsal horn cell dendrites, establishing the initial dorsal horn cell RFs. Rootlet axon RFs in adult cats were used to approximate the RC entry levels of hindlimb skin input. Cord dorsum recordings of monosynaptic field potentials evoked by electrical skin stimulation provided the RC distributions of synaptic input. These were in close agreement. Simulated projections of all 22,000 hindlimb axons were similar to projections predicted from EPSP distributions, and with the observed projections of dorsal roots, cutaneous nerves, and individual axons. The simulated terminals were connected nonselectively to nearby dendrites of 135,000 simulated lamina III-IV cells whose dendritic surface area distributions were based on intracellularly stained cells. There was an overall similarity among pre- and postsynaptic embryonic and adult somatotopies, with a progressive transformation of RF angular location as a function of RC, ML dorsal horn location from an initial embryonic presynaptic concentric pattern to an adult postsynaptic radial one. The initial embryonic dorsal horn cell RF assembly hypothesis was supported by the simulations, as was the additional hypothesis that further refinement of connections would be necessary to establish sufficient selectivity to account for observed adult RFs and somatotopy.

Afferent Pathways↗
PubMed1999

A letter-recognition task to assess lingual tactile acuity.

PURPOSE: This study evaluated a novel neurosensory test based on letter recognition developed for the assessment of spatial acuity of the tongue. PATIENTS AND METHODS: An up-down tracking procedure was used to estimate the threshold height for the recognition of embossed letters of the alphabet examined by the tongue tip. The 48 stimuli consisted of acrylic strips, one side of which bore a letter (A, I, J, L, O, T, U, or W) of 3, 4, 5, 6, 7, or 8 mm in height. Twenty neurologically normal young adults were tested. RESULTS: Stable estimates of the threshold height were obtained after delivery of only 15 trials. Threshold height averaged 5.1 mm (range, 3.7 to 6.6 mm) and was unaffected by gender (P>.88). Although the letters were identified correctly 54% of the time, on average, the tangibility of individual letters varied from 5% correct (for W) to 82% correct (for T). The letter W was never identified by 16 of 20 subjects; T, O, and U were identified by all subjects. Analysis of errors confirmed that subjects relied on spatial cues to make the discriminations; 58% of the incorrect responses were made to 1 or 2 letters with spatial features similar to those of the stimulus letter. CONCLUSIONS: The threshold height for letter recognition can be obtained easily and rapidly, exhibits low among-subject variability, and reflects the capacity to extract and process spatial information. Letters of similar legibility on the tongue should be used to minimize underestimation of subjects' true acuities.

Adolescent↗
PubMed2005

Stimulus-dependent effects on tactile spatial acuity.

BACKGROUND: Previous studies have shown that spatio-tactile acuity is influenced by the clarity of the cortical response in primary somatosensory cortex (SI). Stimulus characteristics such as frequency, amplitude, and location of tactile stimuli presented to the skin have been shown to have a significant effect on the response in SI. The present study observes the effect of changing stimulus parameters of 25 Hz sinusoidal vertical skin displacement stimulation ("flutter") on a human subject's ability to discriminate between two adjacent or near-adjacent skin sites. Based on results obtained from recent neurophysiological studies of the SI response to different conditions of vibrotactile stimulation, we predicted that the addition of 200 Hz vibration to the same site that a two-point flutter stimulus was delivered on the skin would improve a subject's spatio-tactile acuity over that measured with flutter alone. Additionally, similar neurophysiological studies predict that the presence of either a 25 Hz flutter or 200 Hz vibration stimulus on the unattended hand (on the opposite side of the body from the site of two-point limen testing - the condition of bilateral stimulation - which has been shown to evoke less SI cortical activity than the contralateral-only stimulus condition) would decrease a subject's ability to discriminate between two points on the skin. RESULTS: A Bekesy tracking method was employed to track a subject's ability to discriminate between two-point stimuli delivered to the skin. The distance between the two points of stimulation was varied on a trial-by-trial basis, and several different stimulus conditions were examined: (1) The "control" condition, in which 25 Hz flutter stimuli were delivered simultaneously to the two points on the skin of the attended hand, (2) the "complex" condition, in which a combination of 25 Hz flutter and 200 Hz vibration stimuli were delivered to the two points on the attended hand, and (3) a "bilateral" condition, in which 25 Hz flutter was delivered to the two points on the attended hand and a second stimulus (either flutter or vibration) was delivered to the unattended hand. The two-point limen was reduced (i.e., spatial acuity was improved) under the complex stimulus condition when compared to the control stimulus condition. Specifically, whereas adding vibration to the unilateral two-point flutter stimulus improved spatial acuity by 20 to 25%, the two-point limen was not significantly affected by substantial changes in stimulus amplitude (between 100 - 200 microm). In contrast, simultaneous stimulation of the unattended hand (contralateral to the attended site), impaired spatial acuity by 20% with flutter stimulation and by 30% with vibration stimulation. CONCLUSION: It was found that the addition of 200 Hz vibration to a two-point 25 Hz flutter stimulus significantly improved a subject's ability to discriminate between two points on the skin. Since previous studies showed that 200 Hz vibration preferentially evokes activity in cortical area SII and reduces or inhibits the spatial extent of activity in SI in the same hemisphere, the findings in this paper raise the possibility that although SI activity plays a major role in two-point discrimination on the skin, influences relayed to SI from SII in the same hemisphere may contribute importantly to SI's ability to differentially respond to stimuli applied to closely spaced skin points on the same side of the body midline.

Journal Article↗
PubMed2005

Dissociation of phantom limb phenomena from stump tactile spatial acuity and sensory thresholds.

Most amputees experience phantom limb sensations and/or phantom limb pain as well as residual limb (stump) pain that are resistant to treatment. Phantom phenomena are not homogeneous; each patient presents with a unique combination of spontaneous or evoked sensations, pain, and/or awareness. In an effort to understand the underlying mechanisms, postamputation pain has been subclassified based on the perceived sensory qualities reported by the individual. However, little is known about the relationship between subjective phantom phenomena and sensory function of the residual stump. The aim of the present study was to determine if sensory processing, as measured psychophysically, reflected subjective reports of specific qualities of phantom and/or stump sensory phenomena. Twelve individuals who had recently (within 6 months) undergone traumatic unilateral upper extremity amputation participated in the study. Limb temperature, thermal thresholds, tactile sensory thresholds and tactile spatial acuity were compared between the residual limb and the intact limb, and related to patient reports of specific stump and phantom sensory phenomena. All but one subject reported phantom sensations and/or phantom pain. The remaining subject reported only stump pain. Mean skin temperature of the residual limb was significantly lower than that of the intact contralateral limb by approximately 0.9 degrees C in the proximal portion of the stump and 1.7 degrees C at the stump tip. However, the temperature of the stump (compared with the intact limb) did not reflect subjective reports of stump or phantom limb thermal characteristics. Thermal threshold abnormalities differed among patients, and did not suggest any pattern of small fibre loss of function or generalized hyperexcitability. Other than within grafted tissue or near the scar area, skin areas that the patient described as abnormally sensitive or tender to touch were not accompanied by corresponding abnormalities in static tactile thresholds or tactile spatial acuity. Tactile spatial acuity was heightened near the scar area only. The proportion of subjects who had decreased two-point discrimination thresholds at the stump did not differ significantly according to the reporting or non-reporting of dual percepts. Thus, despite a common injury, the sensory abnormalities varied within this cohort of subjects. In addition, psychophysical threshold measures of sensory function did not reflect, in any simple way, subjective phantom phenomena. Therefore, classification of phantom phenomena based on peripheral sensory function may be a misleading step in the search for specific mechanisms underlying postamputation sensory phenomena.

Adult↗
PubMed2003

Short term light deprivation increases tactile spatial acuity in humans.

The effect of short-term light deprivation on tactile spatial acuity was evaluated by asking 28 adult humans to perform a grating orientation task. The 14 subjects who were kept for 90 minutes in complete dark showed, immediately after deprivation, a reversible improvement of tactile spatial acuity. No acuity change was observed in the 14 nondeprived subjects. Results indicate that even a short-term visual deprivation may disclose highly dynamic plastic interactions between visual and tactile systems.

Adaptation, Physiological↗
PubMed2003

Tactile spatial acuity in elderly persons: assessment with grating domes and relationship with manual dexterity.

In this study, we sought to better define the limit of spatial resolution at the fingertips of elderly participants (n = 30, age 60-95 years) using an extended set of JVP grating domes, incorporating four new grating dimensions (2.5-, 3.5-, 4.0- and 4.5-mm width). A secondary aim was to examine whether deficits in tactile acuity could be related to hand dysfunction in older adults. Spatial resolution thresholds were determined by the finest grating whose orientation (dominant index finger) could be reported reliably. Manual dexterity was assessed with the Grooved Pegboard Test (GPT). The extended set of domes improved threshold measurements in a majority of participants (21/30). Still, accurate threshold estimates could not be obtained in one third of the participants, mostly in the older age group (8/9, 74-95 years). Grating resolution thresholds at the index finger were strongly correlated (r = 0.66, p<0.01) with dexterity scores derived from the GPT. From these results, we conclude that the 2.5- and 3.5-mm grating domes are suitable additions when assessing spatial acuity at the fingertips of older subjects between 60 and 70 years of age (mean threshold, 2.7+/-0.6 mm). For the older ones, the 4.0- and 4.5-mm domes can improve threshold measurements but interpretation of values can be complicated by the presence of undiagnosed pathologies (e.g., diffuse polyneuropathy) as people advance in age. The strong relationship between grating resolution thresholds and dexterity scores indicates that an impaired spatial acuity at the fingertips may translate into great difficulties in tasks requiring fine manipulations. These findings have important implications for the assessment of hand function in older adults.

Aged↗
PubMed1999

Grating orientation as a measure of tactile spatial acuity.

Recent studies have used grating orientation as a measure of tactile spatial acuity on the fingerpad. In this task subjects identify the orientation of a grooved surface presented in either the proximal-distal or lateral-medial orientation. Other recent results have suggested that there might be a substantial anisotropy on the fingerpad related to spatial sensitivity. This anisotropy was revealed using a task in which subjects discriminated between a smooth and a grooved surface presented at different orientations on the fingerpad. The anisotropy was substantial enough that it might permit subjects to discriminate grating orientation on the basis of intensive rather than spatial cues. The present study examined the possibility that anisotropy on the fingerpad might provide cues in a spatial acuity task. The ability of subjects to discriminate between a smooth and a grooved surface was measured under conditions that are typically used in grating orientation tasks. No evidence of anisotropy was found. Also, using a grating orientation task, separate estimates were made of sensitivity in the proximal-distal and lateral-medial orientations. Again no evidence of anisotropy was found. Consistent with changes in the density of innervation, grating orientation sensitivity was found to vary as a function of location on the fingerpad. The results support the view that grating orientation is a valid measure of spatial acuity reflecting underlying neural, spatial mechanisms.

Discrimination Learning↗