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Backrests influence the comfort of seated people. With 21 subjects sitting with three backrest heights (no backrest, short backrest, high backrest) discomfort caused by lateral, roll, and fully roll-compensated lateral oscillation was investigated at frequencies between 0.25 and 1.0 Hz. With lateral oscillation, the short backrest reduced discomfort at frequencies less than 0.63 Hz and the high backrest reduced discomfort at frequencies less than 1.0 Hz. With roll oscillation, the high backrest reduced discomfort at frequencies less than 0.63 Hz, but increased discomfort at 1.0 Hz. With fully roll-compensated lateral oscillation, the short backrest reduced discomfort at 0.4 Hz and the high backrest reduced discomfort at 0.5 and 0.63 Hz. As predicted by current standards, a backrest can increase discomfort caused by high frequencies of vibration. However, a backrest can reduce discomfort caused by low frequencies, with the benefit depending on the frequency and direction of oscillation and backrest height. [ABSTRACT FROM AUTHOR]

The discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation has been investigated at frequencies between 0.25 and 1.0 Hz when sitting on a rigid seat and when sitting on a compliant cushion, both without a backrest. Judgements of vibration discomfort and the transmission of lateral and roll oscillation through the seat cushion were obtained with 20 subjects. Relative to the rigid seat, the cushion increased lateral acceleration and roll oscillation at the lower frequencies and also increased discomfort during lateral oscillation (at frequencies less than 0.63 Hz), roll oscillation (at frequencies less than 0.4 Hz), and fully roll-compensated lateral oscillation (at frequencies between 0.315 and 0.5 Hz). The root-sums-of-squares of the frequency-weighted lateral and roll acceleration at the seat surface predicted the greater vibration discomfort when sitting on the cushion. The frequency-dependence of the predicted discomfort may be improved by adjusting the frequency weighting for roll acceleration at frequencies between 0.25 and 1.0 Hz. [ABSTRACT FROM AUTHOR]

Abstract: The method of magnitude estimation is used in psychophysical studies to obtain numerical values for the intensity of perception of environmental stresses (e.g., noise and vibration). The exponent in a power function relating the subjective magnitude of a stimulus (e.g., the degree of discomfort) to the physical magnitude of the stimulus shows the rate of growth of sensations with increasing stimulus magnitude. When judging noise and vibration, there is no basis for deciding whether magnitude estimation should be performed with a reference stimulus (i.e., relative magnitude estimation, RME) or without a reference stimulus (i.e., absolute magnitude estimation, AME). Twenty subjects rated the discomfort caused by thirteen magnitudes of whole-body vertical vibration and 13 levels of noise, by both RME and AME on three occasions. There were high correlations between magnitude estimates of discomfort and the magnitudes of vibration and noise. Both RME and AME provided rates of growth of discomfort with high consistency over the three repetitions. When judging noise, RME was more consistent than AME, with less inter-subject variability in the exponent, n s. When judging vibration, RME was also more consistent than AME, but with greater inter-subject variability in the exponent, n v. When judging vibration, AME may be beneficial because sensations caused by the RME reference stimulus may differ (e.g., occur in a different part of the body) from the sensations caused by the stimuli being judged. [Copyright &y& Elsevier]

Abstract: Lateral acceleration causes discomfort but how the discomfort depends on the frequency of acceleration or characteristics of seating is poorly understood. Using magnitude estimation, twelve male subjects rated the discomfort caused by lateral oscillation at eight frequencies (0.2–1.0 Hz) across four seating conditions (a rigid seat and a train seat, both with and without backrests). Discomfort increased with increasing frequency of lateral acceleration in a similar manner for all four seating conditions. However, at all frequencies and with both seats there was less discomfort when sitting with backrest support than without. Least discomfort occurred on the train seat with backrest and greatest discomfort on the rigid seat without backrest. Current standards predict an additive effect of backrest on vibration discomfort, but the findings show that low frequency lateral acceleration can cause less discomfort when sitting with a backrest than when sitting on the same seat without a backrest. [Copyright &y& Elsevier]

Abstract: Few studies have compared the discomfort caused by vibration in different directions, and few have investigated the vibration discomfort of standing people. This study was designed to compare the discomfort experienced by standing people exposed to sinusoidal vibration in the fore-and-aft, lateral, and vertical directions. Using the method of magnitude estimation, 12 subjects estimated the discomfort caused by 4-Hz sinusoidal vibration at 10 different magnitudes. At 4 Hz, subjects were less sensitive to lateral vibration than to fore-and-aft vibration (Ky /Kx  = 0.71), and more sensitive to vertical vibration than to horizontal vibration (Kz /Kx  = 1.95; Kz /Ky  = 2.77). Previous findings showing how the discomfort of standing people depends on the frequency of fore-and-aft, lateral, and vertical vibration were used to define frequency weightings that reflect relative sensitivity to vibration in each direction. The frequency weightings differ from those appropriate for seated people, and differ from the weightings for standing people in current standards that were mostly derived from understanding of the discomfort of seated people. [Copyright &y& Elsevier]

Abstract: When using vibrotactile thresholds to investigate neuropathy in the fingers, the indentation of a vibrating probe, and the force applied to a static surround around a vibrating probe, affect thresholds. This study was designed to investigate the effects on vibrotactile perception thresholds at the sole of the foot of probe indentation (i.e. height of a vibrating probe relative to a static surround) and the force applied to the static surround. Thresholds at 20Hz (expected to be mediated by the NP I channel) and at 160Hz (expected to be mediated by the Pacinian channel) were obtained at the hallux (i.e. greater toe) and the ball of the foot on 14 healthy subjects. In one condition, the height of the vibrating probe was varied to 0, 1, 2, 3, and 4mm above a static surround with 4-N force applied to the surround. In a second condition, the force applied to the surround was varied to 1, 2, 3, 4, 5, and 6N while using a probe height of 1mm. Thresholds at 20Hz decreased with increasing probe height from 0 to 1mm but showed no significant variation between 2, 3, and 4mm at either the hallux or the ball of the foot. Thresholds at 160Hz decreased with increasing probe height from 0 to 4mm at both the hallux and the ball of the foot. Thresholds at 20Hz obtained with 1-N surround force were higher than thresholds obtained with 2N, but there was no significant difference with surround forces from 2 to 6N at either the hallux or the ball of the foot. Thresholds at 160Hz were unaffected by variations in surround force at the ball of the foot but tended to decrease with increasing force at the hallux. It is concluded that a vibrating probe flush with a static surround, and a surround force in the range 2–4N, are appropriate when measuring vibrotactile thresholds at the hallux and the ball of the foot with a 6-mm diameter contactor and a 2-mm gap to the static surround. [Copyright &y& Elsevier]

Studies of vibration perception in the glabrous skin of the human hand have identified four mechanoreceptor channels, with each channel showing characteristic variations in thresholds with variations in the frequency of vibration and the area of vibration excitation. To advance understanding of the channels mediating vibration perception on the sole of the foot, this study determined how thresholds depend on the frequency of vibration, the location on the foot (the big toe, the ball of the foot, and the heel), and the gap between a vibrating probe and a fixed surround. Thresholds at the three locations were obtained at the 12 preferred one-third octave centre frequencies from 20 to 250 Hz using a 6-mm diameter probe with both a 10-mm and a 20-mm diameter surround. With the 10-mm surround, the displacement thresholds at all three locations showed flat responses from 20 to 40 Hz. With both the 10-mm and the 20-mm surround, the displacement thresholds at the three locations showed 'U-shaped' responses from 40 to 250 Hz. Relative to thresholds obtained with the 20-mm surround, thresholds obtained with the 10-mm surround were lower at the toe and the heel with 20- and 25-Hz vibration, but higher at the ball of the foot with 31.5- to 250-Hz vibration. It is concluded that absolute thresholds for the perception of vibration at the sole of the foot show important variations with location and with contact conditions and tend to be mediated by the NP I channel in the range from about 20 to 40 Hz and the P channel from about 40 to 250 Hz. [ABSTRACT FROM AUTHOR]

Objectives: This study investigated whether the method for eliciting vibration-induced oVEMPs could be improved by applying vibration directly to the teeth, and how vibration-induced oVEMP responses depend on the duration of the applied vibration. Methods: In 10 participants, a hand-held shaker was used to present 100-Hz vibration tone pips to the teeth via a customised bite-bar or to other parts of the head. oVEMP potentials were recorded in response to vibration in three orthogonal directions and five stimulus durations (10-180 ms). The oVEMP responses were analysed in terms of the peak latency onset, peak-to-peak amplitude, and the quality of the trace. Results: Vibration applied to the teeth via the bite-bar produced oVEMPs that were more consistent, of higher quality and of greater amplitude than those evoked by vibration applied to the head. Results: Longer duration stimuli produced longer duration oVEMP responses. Results: One cycle duration stimuli produced responses that were smaller in amplitude and lower quality than the longer stimulus durations. Conclusions: Application of vibration via the teeth using a bite-bar is an effective means of producing oVEMPs. Conclusions: A 1-cycle stimulus is not optimal to evoke an oVEMP because it produces less robust responses than those of longer stimulus duration. Conclusions: A positive relationship between the duration of the stimulus and the response is consistent with the notion that the vibration-induced oVEMP is an oscillatory response to the motion of the head, rather than being a simple reflex response that occurs when the stimulus exceeds a threshold level of stimulation. [ABSTRACT FROM AUTHOR]

Thresholds for the perception of vibration vary with location on the body due to the organization of tactile channels in hairy and non-hairy skin, and variations in receptor density. This study determined vibration thresholds at four locations on the body with two different contactors so as to assist the identification of the tactile channel determining the threshold at each location. Vibrotactile thresholds at six frequencies from 8 to 250 Hz were measured on the distal phalanx of the index finger, the volar forearm, the large toe, and the heel with two contactors: (i) a 1-mm diameter circular probe with a 1-mm gap to a fixed circular surround (i.e., 7.1-mm2 excitation area), and (ii) a 6-mm diameter circular probe with a 2-mm gap to a fixed circular surround (i.e., 79-mm2 excitation area). At all frequencies and with both contactors, thresholds on the fingertip were lower than thresholds on the volar forearm, the large toe, and the heel, consistent with a greater density of mechanoreceptors at the fingertip. Thresholds with the larger contactor were lower than thresholds with the smaller contactor on the fingertip at high frequencies (63, 125, and 250 Hz), on the large toe (except at 250 Hz), on the heel (at all frequencies), and on the volar forearm at 250 Hz. It is concluded that at least two tactile channels (Pacinian from 63 to 250 Hz, and non-Pacinian from 8 to 31.5 Hz) determined vibrotactile thresholds at the fingertip, whereas non-Pacinian channels had a dominant influence on vibrotactile thresholds at the volar forearm. The role of Pacinian and non-Pacinian channels could not be confirmed at the large toe or the heel despite some evidence of spatial summation. [ABSTRACT FROM AUTHOR]

To investigate whether prior exposure to hand-transmitted vibration on the day of a cold provocation test affects the cold response of digital arteries. Each of ten healthy men attended two experimental sessions in which their right hands were exposed for 60 min to either contact force alone (5 N) or a combination of contact force (5 N) and 125-Hz vertical vibration with an acceleration magnitude of 64 m s−2 r.m.s. (unweighted). Finger systolic blood pressure (FSBP) during local cooling to 10°C was measured in the second right finger (exposed hand) and the second left finger (unexposed hand) before exposure and at 30 and 70 min after the end of both exposure conditions. Analysis of repeated measures of FSBP during local cooling by means of an autoregressive model revealed no significant difference in cold-induced vasoconstriction of the digital arteries between exposure to contact force alone and combined exposure to contact force and vibration. There were no significant changes in the cold response of digital arteries over time in either the right or the left hand after exposure of the right hand to either the contact force alone or the combined contact force and vibration. The results of this experimental study of the influence of prior vibration exposure on the cold test results suggest that in healthy men recent exposure to contact force and moderate levels of hand-transmitted vibration does not affect the response of finger circulation to cold provocation. These findings may be of practical importance for the definition of test conditions in the field, especially the length of time required between the last occupational exposure to tool vibration and the commencement of objective vascular testing. [ABSTRACT FROM AUTHOR]

Vibrotactile thresholds depend on the characteristics of the vibration, the location of contact with the skin, and the geometry of the contact with the skin. This experimental study investigated vibrotactile thresholds (from 8 to 250  Hz) at five locations on the distal phalanx of the finger with two contactors: (i) a 1-mm diameter circular probe (0.78-mm 2 area) with a 1-mm gap to a fixed circular surround (i.e., 7.1-mm 2 excitation area), and (ii) a 6-mm diameter circular probe (28-mm 2 area) with a 2-mm gap to a fixed circular surround (i.e., 79-mm 2 excitation area). With both contactors, especially the smaller contactor at low frequencies (i.e., 8, 16, and 31.5  Hz), thresholds decreased towards the tip of the finger, although there was little variation around the whorl. With low frequencies of vibration, and at all five locations on the finger, similar thresholds were obtained with both contactors, consistent with the NPI channel not changing in sensitivity with a change in the area of stimulation. At high frequencies (i.e., 63, 125, and 250  Hz), thresholds were lower with the larger area of stimulation at all locations, except at the extreme tip of the finger, consistent with spatial summation in the Pacinian channel. It is concluded that with a 6-mm diameter contactor, moderate variations in location around the whorl have little influence on the measured thresholds. With the 1-mm diameter contactor there were greater variations in thresholds and extreme locations, near the nail and the distal interphalangeal joint, may be unsuitable for investigating sensorineural disorders. [ABSTRACT FROM AUTHOR]

Objectives. To compare the acute response of finger circulation to continuous and intermittent vibration having the same total duration of vibration exposure and the same energy-equivalent acceleration magnitude. Methods. Finger blood flow (FBF) was measured in the middle and little fingers of both hands of ten healthy men. Finger skin temperature (FST) was measured in the middle right finger. With a static load of 10 N, the middle finger of the right hand was exposed to 125 Hz at 44 m s-2 root mean square (r.m.s.) in five conditions: (1) 30 min continuous exposure, (2) two periods of 15 min, separated by a 15 min period with no vibration, (3) four periods of 7.5 min, separated by 7.5 min periods with no vibration, (4) eight periods of 3.75 min, separated by 3.75 min periods with no vibration, (5) 16 periods of 1.88 min, separated by 1.88 min periods with no vibration. All five exposures correspond to an 8 h energy-equivalent frequency-weighted acceleration magnitude of 1.4 m s-2 r.m.s. according to International Standard ISO 5349–1 (2001). Finger circulation was measured in all four digits before the application of vibration and at fixed intervals during vibration exposure and during a 45 min recovery period. Results. The FST did not change during vibration exposure, whereas all vibration conditions produced significant reductions in FBF of the vibrated finger when compared with the pre-exposure FBF. During vibration exposure, the vibration caused a similar degree of vasoconstriction in the vibrated finger without evidence of cumulative effects during intermittent exposure. After the end of exposure to 30 min of continuous vibration there was a progressive decrease in the FBF, whereas there was no statistically significant reduction following exposure to intermittent vibration. Conclusions. For the vibration stimuli investigated (exposure durations varying from 1.88 min to 30 min, with rest periods varying from 1.88 min to 15 min), the reduction of FBF during exposure was the same for continuous and intermittent vibration. The after effect of vibration was greater following the continuous vibration exposure. Although some evidence from this study is consistent with the notion that intermittent vibration has a less severe effect than continuous vibration, this evidence is not yet conclusive. [ABSTRACT FROM AUTHOR]