The influence of rate of skin indentation on threshold and suprathreshold tactile sensations.

The effects of skin indentation depth and rate on threshold and suprathreshold tactile sensations were investigated. Indentation rates between 0.3 and 10 mm/sec had little effect on the absolute tactile thresholds measured in terms of indentation depth. Slower rates resulted in increased absolute thresholds. Estimates of the growth in intensity of tactile sensations were made as functions of indentation depth and rate. The fastest rate used (10 mm/sec), for a given depth of indentation, produced the most intense sensation; the slowest (0.1 mm/sec), the least intense sensation. The tactile sensation magnitude estimates, with rate as the parameter, could be described by power functions. At the slowest indentation rate the exponent of the function was 1.36. At faster indentation rates (0.4, 1.0, and 10 mm/sec), two functions of markedly different slopes were required to describe the estimates. The exponents of the power functions were between 0.38 and 0.49 for indentation depths up to about 0.9 mm, and between 1.07 and 1.43 for deeper indentation depths.