Effect of contact location on vibrotactile thresholds at the fingertip

Abstract

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.

Vibrotactile thresholds at the fingertip, volar forearm, large toe, and heel

“…It seems probable that, within each frequency, the same channel mediated thresholds with both the small and the large contactor, since thresholds obtained with both contactors were correlated at all frequencies (Table 4) except at 16 Hz. The pattern of correlations, both between frequencies, and between contactors, as well as the spatial summation only occurring at high frequencies, implies that thresholds at high frequencies (63, 125 and 250 Hz) were determined by the Pacinian channel with both contactors and that thresholds at lower frequencies (8, 16 and 31.5) were determined by non-Pacinian channels with both contactors, consistent with Whitehouse et al (2006).…”

Spatial summation of vibrotactile sensations at the foot

“…At the fingertip, 160-Hz thresholds increased as the probe diameter reduced from 10 to 1 mm, consistent with mediation by the Pacinian channel [7,8,9]. There was a significant difference between thresholds obtained with 1-mm and 3-mm probes, unlike the thenar eminence, because at the fingertip the Pacinian channel is most sensitive even with a 1-mm probe [7].…”

“…With 300-Hz vibration, thresholds reduced with a slope of 3 dB per doubling of contactor area between 0.025 and 0.10 cm 2 (probes with diameters of 1.8 and 3.6 mm), but not between 0.38 and 0.75 cm 2 (probes with diameters of 7 and 10 mm). Whitehouse et al [8] studied vibrotactile thresholds at the fingertip with excitation areas of 0.071 and 0.79 cm 2 , and observed lower thresholds with larger excitation areas at 63, 125 and 250 Hz, but not at 8, 16 and 31.5 Hz. Morioka et al [9] obtained vibrotactile thresholds at the fingertip with excitation areas of 0.071 cm 2 (1-mm diameter probe) and 0.79 cm 2 (6-mm diameter probe) and found that thresholds at 63, 125 and 250 Hz, where thresholds were believed to be determined by the Pacinian channel, were on average 10.2 dB lower with the larger probe.…”

Measurements of Vibrotactile Perception Thresholds at the Fingertips in Poland

“…The VPT curve is also significantly influenced by the size of the probe. For a probe 1 mm in diameter, the VPT values were lower at the stimulus frequencies of 8 and 16 Hz and higher at frequencies of above 125 Hz in comparison with the values obtained using a 6-mm probe 14) . The mean VPT values obtained with a P8 pallesthesiometer in this study are higher at the frequencies of 4 Hz, 25 Hz, 31.5 Hz and 125 Hz in comparison with the VPTs contained in Annex A of the ISO 13091-2 15) .…”