Fig. 2.

(A) Experimental protocol. Participants were asked to compare the slipperiness of two surfaces. The reference and comparison were presented in random order. (B) Probability of a participant perceiving the difference in friction as a function of the amplitude of vibration of the ultrasonic lubrication. The higher the amplitude of ultrasonic vibration is, the lower the friction coefficient. The dashed line represents the fit with a psychometric function. Individual performances are represented as gray dots. The chance level is represented by the dashed line. (C) Displacement and resulting strain of the skin for the cases of high friction (Left) and low friction (Right).