Difference thresholds for vibration of the foot: Dependence on frequency and magnitude of vibration

Abstract: The smallest change in vibration intensity for the change to be perceptible (i.e. intensity difference threshold) has not previously been reported for vibration of the foot. This study investigated the influence of vibration magnitude and vibration frequency on intensity difference thresholds for the perception of vertical sinusoidal vibration of the foot. It was hypothesised that relative intensity difference thresholds (i.e. Weber fractions) for 16-Hz vibration mediated by the non-Pacinian I (NPI) channel would differ from relative intensity difference thresholds for 125-Hz vibration mediated by the Pacinian (P) channel. Absolute thresholds, difference thresholds, and the locations of vibration sensation caused by vertical vibration of the right foot were determined for 12 subjects using the up-down-transformed-response method together with the three-down-one-up rule. The difference thresholds and locations of sensation were obtained at six reference magnitudes (at 6, 9, 12, 18, 24, 30dB above absolute threshold—i.e. sensation levels, SL). For 16-Hz vibration, the median relative difference thresholds were not significantly dependent on vibration magnitude and were in the range 0.19 (at 30dB SL) to 0.27 (at 9dB SL). For 125-Hz vibration, the median relative difference thresholds varied between 0.17 (at 9dB SL) and 0.34 (at 30dB SL), with difference thresholds from 6 to 12dB SL significantly less than those from 18 to 30dB SL. At vibration magnitudes slightly in excess of absolute thresholds (i.e. 6–12dB SL) there were no significant differences between Weber fractions obtained from the P channel (at 125Hz) and the NPI channel (at 16Hz). At 24 and 30dB SL, the 125-Hz Weber fractions were significantly greater than the 16-Hz Weber fractions. Differences in the 125-Hz Weber fractions may have been caused by a reduction in the discriminability of the P channel at high levels of excitation, resulting in one or more NP channel mediating the difference thresholds at magnitudes greater than 18dB SL. At high magnitudes, a change of channel mediating the Weber fractions may have been responsible for different Weber fractions with 16- and 125-Hz vibration. [Copyright &y& Elsevier]