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At least 19 recordsLinked to original sources
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↗
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↗
PubMed1997

Tactile spatial acuity and roughness discrimination: impairments due to aging and Parkinson's disease.

We used gratings of alternating ridges and grooves in a quantitative psychophysical investigation of tactile perception in patients with Parkinson's disease (PD) and age-matched normal controls. The groove width required for threshold discrimination of grating orientation was 25% higher in the control subjects compared to younger individuals studied previously (p = 0.004), indicating a small but significant decline in tactile spatial acuity with age. Relative to age-matched controls, patients with PD showed a twofold increase in the tactile spatial threshold (p = 3.07 x 10(-8), with somewhat greater impairment on the side more affected clinically (p = 0.03). Testing with the forearm prone, as compared to supine, produced a small improvement in the acuity of patients (p = 0.01) but not controls (p = 0.26). PD patients were also impaired in tactually discriminating grating roughness: their difference limens were over three times higher than those of controls (p = 5.74 x 10(-5)) for gratings differing in groove width, and over twice as high (p = 0.0003) for gratings differing in ridge width. We conclude that PD significantly impairs performance on these tactile tasks.

Adult↗
PubMed1996

Tactile spatial acuity at the human fingertip and lip: bilateral symmetry and interdigit variability.

We used the spatial threshold for discrimination of grating orientation to assess tactile spatial acuity at the lower lip and each fingertip, bilaterally, in seven normal human subjects. We confirmed previous findings that: (1) this test is highly reliable, and (2) acuity at the lip is substantially higher than at the fingertips. In addition, we showed that: (1) acuity does not differ significantly between right and left sides, and (2) among fingertips, acuity is lowest at the fifth digit and comparable on the other digits.

Analysis of Variance↗
PubMed1979

Sensations from surgically transferred glabrous skin; central versus peripheral factors.

In reinnervated skin transferred from the foot to the hand, sensory thresholds approach normal values--an observation not predicted by the theoretical relationship between innervation density and tactile acuity. Therefore, we suggest that innervation density is not the major factor determining tactile acuity. Rather, the hand region of the central somesthetic map may be specialized to provide a calibre of function unavailable to other regions.

Humans↗
PubMed1993

A laboratory exercise in somesthesis that is expeditious, inexpensive, and suitable for large classes.

A teaching laboratory is described that demonstrates two principles of the somatosensory system: 1) the "spot-like" nature of skin sensitivity and 2) tactile acuity. This laboratory has been used for a large medical school class (140-160 students). One reason for the success of this laboratory is the ability to provide a sufficient number of stimulating apparatuses. The two-point discrimination device used to measure tactile acuity can be made easily and cheaply. In addition, two other demonstrations are described that are suitable for smaller classes or that students can do on their own. Although this lab was designed for medical students, the content makes it suitable for undergraduate or high school students.

Humans↗
PubMed1990

Coding of stimulus location and intensity in populations of mechanosensitive nerve fibers of the raccoon: I. Single fiber response properties.

The primary aim of this study was to determine and compare the receptive field (RF) characteristics and response properties of single mechanosensitive nerve fibers innervating the glabrous skin of the forepaw and hindpaw of the raccoon. The action potentials of 129 median nerve fibers and 61 posterior tibial nerve fibers were recorded in response to punctate mechanical stimuli varying in location and intensity. The stimuli were delivered to six standard test sites on digit 1 and the contiguous pads of each paw. Attempts were made to classify each fiber according to its rate of adaptation to sustained stimulation; the RF of each fiber was mapped using a standard series of stimulus intensities. The results indicated that the response properties of individual fibers were highly complex and depended on the location and intensity of stimulation. 1) The distributions of absolute threshold were not different for the median or tibial nerve fibers or for different classes of fibers based on adaptation rate. A distal to proximal increase in threshold was found for each paw, suggesting a corresponding gradient of sensitivity across the glabrous skin. 2) Threshold RF areas did not vary across either paw nor did they differ between the two paws. Suprathreshold RFs were quite large relative to expected tactile acuity and displayed complex features. 3) Response properties such as adaptation rate, on- and off-responses, were found to vary with both stimulus location and intensity. It was concluded that the responses of individual nerve fibers could not uniquely encode any stimulus parameter tested, and that the properties of single fibers could not account for apparent differences in tactile acuity across each paw or between the two paws.

Action Potentials↗
PubMedDate not supplied

Light touch thresholds in diabetic patients.

To determine whether touch acuity is altered in individuals with maturity-onset diabetes, tactile thresholds on the pad of the index finger of 32 diabetic and 27 nondiabetic subjects were compared. A set of modified Von Frey hairs was used to present touch stimuli in a forced-choice tracking procedure that controls for subject response bias. The mean tactile threshold of diabetic patients was significantly higher than that of nondiabetic subjects, although the difference between the two groups is small. Within the diabetic group, decreased tactile acuity was associated with a longer duration of disease diagnosis, presence of insulin therapy, and low-digit temperature. However, reported presence or absence of peripheral sensory symptoms (tingling, numbness, etc.) in diabetic patients did not relate to touch thresholds. The small but significant increase in touch threshold that was observed in diabetic individuals may provide an early indication of sensory neuropathy. Further use of threshold determinations will contribute to our understanding of sensory changes that accompany diabetes.

Adult↗
PubMed1978

Somatotopic organization of mechanosensory projections to SII cerebral neocortex in the raccoon (Procyon lotor).

The pattern of projections of peripheral receptors to the neocortex in the second somesthetic receiving area (SII) was mapped in raccoons. The purpose was to determine if the projection area of peripheral receptors to the forepaw area in the SII region is disproportionally enlarged as it is in SI. Tungsten microelectrode recording procedures were used to map thoroughly the inferior wall of the suprasylvian sulcus for regions responsive to mechanical stimulation of peripheral receptors. The results show that: 1. The forepaw area in SII shows an enlargement commensurate with that found in the SI. This suggests that those factors that are selective for tactile acuity of the raccoon forepaw were operating in the evolution of SII as they were in SI. 2. The somatotopic organization of mechanoreceptive projections to SII is reversed mediolaterally compared to previous descriptions of this arrangement in other mammals: projections form axial structures lie medially and those from apical structures lie laterally along the inferior bank of the suprasylvian sulcus in the raccoon.

Animals↗
PubMed1980

A comparison of human tactile stimulus velocity discrimination with the ability of S-I cortical neurons in awake rhesus monkeys to signal the same velocity differences before and after non-anesthetic doses of pentobarbital.

Using psychophysical techniques, the ability of human subjects to discriminate the velocity of brush movement across the glabrous skin of the hand was determined. The same stimulus was then used in a series of neurophysiological experiments designed to determine the ability of neurons in the primary somatosensory cortex (S-I) of awake rhesus monkeys to signal differences in the same velocities. Analysis of the data in signal detection theory terms revealed that humans could discriminate two velocities (132 and 182 mm/sec) much better than most of the cortical cells of the monkeys could signal the differences in those same velocities by changes in their stimulus induced mean firing frequency. However, 4 of the 37 cells studied signaled the differences as well as the human observers. Non-anesthetic doses of pentobarbital (1-20 mg/kg) caused a reduction in the firing frequency of the S-I neurons but at the same time enhanced the difference in firing frequency elicited by the two different stimulus velocities. This enhancement in the difference between the firing frequencies was caused by a relatively greater suppression of neuronal activity elicited by the slower velocity. These results not only point out potential problems with the use of barbiturates in neurophysiological studies and by humans who require fine tactile acuity, but they also raise important questions about coding by S-I cells. The reduction in overall neuronal activity accompanied by the enhancement of the difference in firing frequency at the two velocities would suggest that, if firing frequency is coding for stimulus presence or velocity, at 8 mg/kg the monkeys may have a more difficult time detecting the stimulus but an easier time discriminating between different velocities of the stimulus.

Animals↗
PubMed1990

Coding of stimulus location and intensity in populations of mechanosensitive nerve fibers of the raccoon: II. Across-fiber response patterns.

The major aim of this study was to determine whether information about stimulus location and intensity can be precisely encoded in the population response profiles of mechanosensitive nerve fibers. Across-fiber patterns (AFPs) were reconstructed using data obtained previously (58) from 129 single median nerve fibers and 61 posterior tibial nerve fibers of the raccoon. Punctate mechanical stimuli of varying intensities were presented to six standard test sites on the glabrous skin of the forepaw and hindpaw, and the AFP produced by each unique stimulus was determined. Innervation density (ID) at each of the test sites was estimated from the integrated voltage of compound action potentials evoked by constant current stimulation of the skin at each site. Differences in ID between corresponding regions of the forepaw and hindpaw were estimated by counts of myelinated fibers and measurements of skin areas supplied by the median and tibial nerves, respectively. All AFPs were adjusted to take into account the differences in ID among the various skin sites on the two paws. The data indicated that different stimulus locations and intensities on each paw could be precisely and unambiguously encoded by AFPs; location was represented primarily by the shape of the AFP, whereas intensity was represented by the height of the AFP. The discriminability of location and intensity was shown to be directly related to the magnitude of the difference between the AFPs elicited by any two stimuli. Consistent with expectations, AFPs for stimuli delivered distally on each paw showed greater differences as a function of stimulus location and intensity than AFPs for stimuli applied proximally. Furthermore, AFPs produced by stimuli to the forepaw showed greater changes than AFPs for stimuli to comparable sites on the hindpaw. It was concluded that systematic differences in the population response profiles of median and tibial nerve fibers could account for regional variations in tactile acuity across each paw and differences between the two paws.

Afferent Pathways↗
PubMed1998

Spatiotemporal stability of lip movements in older adult speakers.

Although the intelligibility of healthy older adults normally seems unimpaired, age-related changes occur in sensorimotor components of the speech system and in such global parameters as speech rate. In order to clarify the effect of these changes on the variability of speech movements, we examined oral peripheral abilities, speech rate, and speech kinematics in a group of 10 adults age 76-83, compared to a group of 10 young adults. Participants repeated a short phrase 15 times at habitual, fast, and slow rates. The resulting lip displacement signals were time- and amplitude-normalized, and successive standard deviations along the movement waveforms were summed to produce a spatiotemporal index (STI) representing individual variability in movement pattern. Participants tended to show greatest variability at slow rate, less variability at fast rate, and least variability at habitual rate. For the older adults, STI at habitual rate was significantly higher (more variable) and speech durations were longer than those of young adults. Perioral strength and tactile acuity were poorer in these older adults than in young adults. We conclude that as sensorimotor abilities change in old age, speakers are less consistent in the spatiotemporal organization of speech movements, reflecting decreased stability of speech motor control.

Adult↗
PubMed1990

Accuracy of weight estimation for weights lifted by proximal and distal muscles of the human upper limb.

1. It is well established that tactile acuity is greater over digits than over the proximal parts of the upper limb and that the corticospinal projection is especially dense for distal muscles. To determine whether the acuity for judgements of forces exerted by distal muscles differed from that for proximal muscles, a weight-matching task was used with first dorsal interosseous, flexor pollicus longus and elbow flexors. 2. Reference weights equivalent to approximately 3% (light) and 15% (heavy) of the maximal voluntary contraction were lifted by one muscle group on the left. They were matched with a variable weight, lifted by the same group, on the right. 3. In naive subjects, the coefficient of variation for repeated estimates of perceived heaviness was significantly lower for proximal than distal muscles. Measured in this way, 'accuracy' (i.e. reproducibility of the estimates) was not greater for the intrinsic muscles of the hand. This result could not be explained by the way in which the weights were supported by the index finger. When the data were expressed as the relative difference between the reference and the matched weight, each muscle group behaved similarly. 4. For a particular muscle, accuracy was greater when the heavy rather than the light weights were lifted. 5. Given that estimates of forces and heaviness are biased by signals of central motor command (McCloskey, 1981; Gandevia, 1987; Cafarelli, 1988; Jones, 1988). these signals could be graded no more finely for distal than proximal muscles. Furthermore, relative accuracy was greater for forces at the high rather than the low end of the comfortable 'matching' range of force for a particular muscle.

Adult↗
PubMed1995

Sensitivity of the mystacial vibrissae of harbour seals (Phoca vitulina) for size differences of actively touched objects.

We studied the capability of one male and one female harbour seal Phoca vitulina to discriminate diameter differences of circular discs by means of active touch with their mystacial vibrissae. To prevent the animals from perceiving visual information, they were blindfolded during trials. In a two-alternative forced-choice procedure, the seals were required to choose the larger of two Perspex discs. Weber fractions c (the ratio of the lowest diameter difference detected by the seals on 75% of occasions to the starting disc diameter D, delta D/D = c) were determined for three standard discs (diameters 1.12cm, 5.04cm and 8.74cm) by the psychophysical method of limits. While the seals achieved Weber fractions of 0.29 (male) and 0.26 (female) at the smallest standard disc, their performance improved with increasing disc size, resulting in an approximately constant Weber fraction of 0.13 (male) and 0.08 (female) for the two larger standard discs. The difference in performance between the two seals did not reflect a real difference in sensitivity, but may best be explained by a difference in choice behaviour. As a measure of tactile acuity, the Weber fractions obtained for the larger standard discs indicate that harbour seals can use their mystacial vibrissae as efficiently for active touch as monkeys use their hands.

Animals↗
PubMed1993

Tactile-evoked response of sensory fibers in buccal and submandibular regions of the rat.

Evoked neural responses to tactile stimulation were recorded electrophysiologically from the mechanoreceptive afferent fibers innervating the buccal and submandibular regions of Wistar rats anesthetized with sodium thiopental. Miniature probes 200 microns in diameter were used, and data analysis was performed on the mechanosensitivity of responses to tactile stimulation in the areas innervated by the mental, mylohyoid, auriculotemporal, and cervical nerves. Mechano-sensitivity of each area showed a characteristic distribution of slowly adapting (SA), rapidly adapting (RA), C-fiber (CF), and hair follicle (HF) units in individual receptive fields. The density of the SA units was high in the areas innervated by the mylohyoid and auriculotemporal nerves. The CF units were concentrated in the small dome in the area of the mylohyoid nerve and the auriculotemporal nerve, as shown by a significant response to the dynamic features of stimulation. Estimation of the current needed for tactile acuity suggests an important role of the SA fibers in the areas innervated by the auriculotemporal, mylohyoid, and cervical nerves.

Afferent Pathways↗