Published as: Vibrotactile thresholds at the fingertip, volar forearm, large toe and heel Morioka, M., Whitehouse, D. J. & Griffin, M. J. 2008 In : Somatosensory & Motor Research. 25, 2, p. 101-112. 2 AbstractThresholds for the perception of vibration vary with location on the body due to the organisation 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-mm 2 excitation area), and (ii) a 6-mm diameter circular probe with a 2-mm gap to a fixed circular surround (i.e. 79-mm 2 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.Published as: Vibrotactile thresholds at the fingertip, volar forearm, large toe and heel Morioka, M., Whitehouse, D.

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.

Objectives: Vibrotactile thresholds on the ®ngers were compared using two alternative methods of controlling contact with a vibrating probe: control of the force of contact with the probe (force control) and control of skin indentation produced by the probe (indentation control). Both systems had the same control of push force on a static surround around the vibrating probe. Method: A group of 14 male subjects (aged 20±27 years) were tested at four frequencies (31.5, 63, 125, 250 Hz) in three separate sessions so as to quantify the repeatability of thresholds. Skin stiness was also measured. Results: Control of skin indentation gave more repeatable thresholds than control of probe force. There was a practice eect whereby thresholds became more consistent over sessions. There were no systematic correlations between thresholds and skin stiness. Conclusions: Repeatable and similar vibrotactile thresholds can be obtained with two alternative methods having different contact conditions. Either method may assist the diagnosis of disorders associated with hand-transmitted vibration, but control of skin indentation has the advantage of greater simplicity and, in this study, greater repeatability.