Scc68

Electrotactile non-uniform white noise was applied at the posterior thigh (see Figure 1A) within a frequency band of 0–50 Hz (the band must contain the target frequency of 30 Hz to allow for the resonance effect). Electrical noise was generated with a custom LabVIEW^® program and output via a DAQ interface (SCC68, National Instruments, Austin, TX, United States) to a constant current isolated stimulator (A395, World Precision Instruments, Sarasota, FL, United States) through two 34 mm round sensor adhesive electrodes (Ambu^® BlueSensor M, Ambu Sdn. Bhd., Penanq, Malaysia) affixed to the skin with Transpore^® medical tape on either side of the SR location.

Vibration at the test site was produced using a probe of 6 mm diameter attached to an electromagnetic vibrator (mini-shaker type 4810, Bruel and Kjaer, Naerum, Denmark), and applied perpendicularly to the skin (see Figure 1A). Vibration frequency was set to 30 Hz to preferentially activate the FAI receptors (Toma and Nakajima, 1995 (link)). The frequency was delivered using a custom program in LabVIEW^® and a custom-built BNC breakout box and amplified (Power Amplifier Type 2719, Bruel and Kjaer, Naerum, Denmark). Acceleration and force data were collected (acceleration - model 2221D, Endevco, CA, United States; force – Model 31 load cell, Honeywell, MN, United States) at a sampling frequency of 1000 Hz (BNC-2111, National Instruments, Austin, TX, United States). Displacement of the probe was measured by a custom sensor (model RGH24Z, Renishaw, Gloucestershire, United Kingdom) and input via a DAQ interface (SCC68, National Instruments, Austin, TX, United States) into the custom LabVIEW^® program.