Larger contactor area increases low-frequency vibratory sensitivity in hairy skin

Background In research, assessing vibratory cutaneous sensitivity is an important research branch to quantify various diseases or to develop devices for pattern recognition. The measured vibration perception thresholds (VPTs), however, are subjective and usually result in a large data variability. This might induce difficulties to detect differences, for example, when comparing different anatomical locations. Hence, a higher ability to detect changes is desirable. Another feature of VPTs is spatial summation, but in the literature it is controversially discussed whether or not this phenomenon is also present in the lower frequency range. For these reasons, the present study aimed to investigate whether an enlarged matrix contactor area (measured at the hairy skin) induces improvements in subjective sensitivity using high and low frequencies, and whether a large contactor area is better able to identify changes of VPTs than a small contactor area of a single contactor. For each frequency, we hypothesized an increased sensitivity for the matrix compared to the single contactor. We also hypothesized that changes can be better-detected between the anatomical locations when using the matrix than the single contactor. Methods Twenty healthy and young participants voluntarily took part in this study. Three anatomical locations at the torso were measured at the middle aspect of the lower back, middle lateral aspect of the upper arm, and the region just below the armpit. At each location, two frequencies (30, 200 Hz) and two contactor conditions (single contactor: 0.48 cm2 , contactor matrix: 9 × 0.48 cm2 = 4.32 cm2) were tested in a randomized order. Results Supporting our hypothesis, we found that improved cutaneous sensitivity after increasing the contactor size occurs not only at high, but also at low frequencies at all anatomical locations. Large contactor sizes resulted in higher sensitivity and in a superior ability to detect changes. The superior behavior of the matrix to exhibit a lower variability could not always be proven. This work may be relevant for future studies aiming to identify changes of VPTs in various patient groups, for example.

Effects of Psychophysical Scaling Method, Body Test-Site, and Skin-Contactor Surface Area on Vibrotactile Magnitude Functions

This study was designed to focus on possible interactive effects that scaling method, body test-site, and skin-contactor surface area might have on vibrotactile magnitude functions. The psychophysical scaling methods of magnitude estimation and magnitude production were used to apply vibrotactile stimulation to the anterior midline of the tongue and the thenar eminence of the hand through the use of three skin-contactor areas (.128, .320, and 1.30 cm3). Ten subjects, ranging in age from 19 to 21 yr. ( M age = 19.8 yr.) were employed. Data obtained from the 10 subjects suggested that the suprathreshold-scaling method chosen can be a significant determinant of the findings obtained. They further suggested that the tongue and hand may respond differently to suprathreshold vibrotactile stimulation and that the effects of varying skin-contactor area may be different for the two body-sites tested.