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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]

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]

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]