The vibration stimulus. Effects of viscous-elastic resistance of skin on the amplitude of vibrations.

Accurate measurements of the vibration amplitude were Fig. 7. Reproducibility of double determinations of the vibratory perception threshold (log V2) in normal persons and uraemic patients. PH=pulp, big toe; MM=medial malleolus. Axes show read values in volts transformed into a log V2 scale. Full and strippled lines indicate mean and 95% confidence limits of expected variation (ref. Table II). Made possible by a piezo-electric transducer (accelerometer). With constant voltage to the vibrator slight compression of the tactor against the skin produced an increase in amplitude, similar to that seen with compression against a rubber diaphragm. Further compression had a variable effect on the vibration amplitude, depending on the nature of the underlying tissue (bone, soft tissue). An exact calibration of the vibration stimulus strength therefore appears impossible, and a comparison of the acuity of vibratory perception is invalidated by the different viscous-elastic protion amplitude and the square of the voltage, as seen for vibrations in air, was also demonstrable between independent measurements of the vibratory perception threshold (VPT) in the two terms. The intra- and interindividual variations in terms of the amplitude and the square of the voltage were of the same order. On a logarithmic scale the reproducibility of VPT was independent of the threshold stimulus strength.