Physiological noise and its influence on vibrotactile perception thresholds.

Vibration of physiological origin (physiological noise) was studied when a small diameter probe, attached to a vibrator and accelerometer for the determination of vibrotactile perception thresholds, was held in contact with a fingertip. The acceleration spectrum consisted of a broad plateau between 0.1 and 10 Hz, where the power spectral density was about -20 dB re 1 (m/s2)2/Hz, and it fell rapidly with increasing frequency above 10 Hz. Substantial contributions from respiration (0.2-1 Hz), blood circulation (1-5 Hz), and hand tremor (6-8 Hz) could be identified. The physiological noise was largely independent of subject, contact force, and probe diameter, and it was approximately equal in amplitude to the threshold of the vibrotactile perception. Current knowledge of the masking and adaptation of vibrotactile signals indicates that vibrotactile thresholds in the frequency range 2-250 Hz may be influenced by the magnitude of this physiological noise under some conditions of flesh stimulation.