The Measurement of the Sensitivity of the Skin to Mechanical Vibration

Vibration sensing the mammalian way: an artificial Pacinian corpuscle

A vibration sensor is presented mimicking the structure of the Pacinian corpuscle. A multi-step casting process is used to create a 5 mm diameter sensor with a liquid metal core, elastomer dielectric, and graphite counter electrode creating a spherical capacitive sensing element with sensitivities on the order of 10 Δ pF/mm^-1. A model for the capacitance change of the spherical capacitor as it is formed is developed and its findings support the sensitivities observed. Various elastomer dielectric compositions with integrated barium titanate nanoparticles are tested to increase the dielectric constant. The biological acoustic filter within the corpuscle is mimicked using alternating cast layers of oligomers and elastomers around the spherical sensor element. Vibration sensing is characterized over the low frequency range of 10-300 Hz and the minimum detectable sensitivity is found to be 1 µm with a low power requirement of 7 mW. The artificial Pacinian corpuscle has potential applications in tactile sensing and seismic monitoring devices.

Vibrotactile sensitivity threshold: nonlinear stochastic mechanotransduction model of the Pacinian Corpuscle

Based on recent discoveries of stretch and voltage activated ion channels in the receptive area of the Pacinian Corpuscle (PC), this paper describes a two-stage mechanotransduction model of its near threshold Vibrotactile (VT) sensitivity valid over 10 Hz to a few kHz. The model is based on the nonlinear and stochastic behavior of the ion channels represented as dependent charge sources loaded with membrane impedance. It simulates the neural response of the PC considering the morphological and statistical properties of the receptor potential and action potential with the help of an adaptive relaxation pulse frequency modulator. This model also simulates the plateaus and nonmonotonic saturation of spike rate characteristics. The stochastic simulation based on the addition of mechanical and neural noise describes that the VT Sensitivity Threshold (VTST) at higher frequencies is more noise dependent. Above 800 Hz even a SNR = 150 improves the neurophysiological VTST more than 3 dBμ. In that frequency range, an absence of the entrainment threshold and a lower sensitivity index near the absolute threshold make the upper bound of the psychophysical VTST more dependent on the experimental protocol and physical set-up. This model can be extended to simulate the neural response of a group of PCs.

Vibrissal sensitivity in a harbor seal (Phoca vitulina)

Prior efforts to characterize the capabilities of the vibrissal system in seals have yielded conflicting results. Here we measured the sensitivity of the vibrissal system of a harbor seal (Phoca vitulina) to directly coupled sinusoidal stimuli delivered by a vibrating plate. A trained seal was tested in a psychophysical paradigm to determine the smallest velocity that was detectable at nine frequencies ranging from 10 Hz to 1000 Hz. The stimulus plate was driven by a vibration shaker and the velocity of the plate at each frequency-amplitude combination was calibrated with a laser vibrometer. To prevent cueing from other sensory stimuli, the seal was fitted with a blindfold and headphones playing broadband masking noise. The seal was sensitive to vibrations across the range of frequencies tested, with best sensitivity of 0.09 mm/s at 80 Hz. Velocity thresholds as a function of frequency showed a characteristic U-shaped curve with decreasing sensitivity below 20 Hz and above 250 Hz. To ground-truth the experimental setup, four human subjects were tested in the same paradigm using their thumb to contact the vibrating plate. Threshold measurements for the humans were similar to those of the seal, demonstrating comparable tactile sensitivity for their structurally different mechanoreceptive systems. The thresholds measured for the harbor seal in this study were about 100 times more sensitive than previous in-air measures of vibrissal sensitivity for this species. The results were similar to those reported by others for the detection of waterborne vibrations, but show an extended range of frequency sensitivity.

Vibrotactile performance by normal and hearing-impaired subjects using two commercially available vibrators

The aim of this study was to measure vibrotactile sensitivity and stress pattern recognition of untrained normal-hearing and hearing-impaired subjects. Vibrotactile thresholds were measured as a function of frequency with two vibrators at three body placements. Stress pattern recognition was tested with two vibrators at two body placements. Vibrotactile threshold results indicate that wrist placements were less sensitive than fingertip placement and the hearing-impaired subjects were equally or less sensitive than the normal-hearing subjects. Vibrator plunger size had the greatest effect on threshold in the most sensitive frequency range of the skin. Stress pattern recognition results indicate that subject performance is a function of body placement but not a function of plunger size. Moreover, stress pattern recognition curves obtained in this study had lower plateaus for the hearing-impaired subjects than for the normal-hearing subjects. Implications for vibrotactile training are discussed.

Physiologic and physical factors that govern the clinical appreciation of cardiac thrills

Palpable cardiac thrills have been considered valuable diagnostic findings. The present study indicates that they add little information to that obtained by careful evaluation of auscultatory findings, and that the quality of cardiac murmurs is a much safer guide in diagnosis than are the palpable vibrations produced by the same mechanism.