The tactile perception of transient changes in friction

Abstract

When we touch an object or explore a texture, frictional strains are induced by the tactile interactions with the surface of the object. Little is known about how these interactions are perceived, although it becomes crucial for the nascent industry of interactive displays with haptic feedback (e.g. smartphones and tablets) where tactile feedback based on friction modulation is particularly relevant. To investigate the human perception of frictional strains, we mounted a high-fidelity friction modulating ultrasonic device on a robotic platform performing controlled rubbing of the fingertip and asked participants to detect induced decreases of friction during a forced-choice task. The ability to perceive the changes in friction was found to follow Weber's Law of just noticeable differences, as it consistently depended on the ratio between the reduction in tangential force and the pre-stimulation tangential force. The Weber fraction was 0.11 in all conditions demonstrating a very high sensitivity to transient changes in friction. Humid fingers experienced less friction reduction than drier ones for the same intensity of ultrasonic vibration but the Weber fraction for detecting changes in friction was not influenced by the humidity of the skin.

The Perception of Ultrasonic Square Reductions of Friction With Variable Sharpness and Duration

“…This phenomenon could also have a perceptual influence. A recent study estimated the 75% just noticeable difference for such stimuli to be 11% [10], which implies that in many trials performed with a fast speed, the first pulse may be barely noticeable or undetected while the second one is largely above the perceptual threshold.…”

“…The stabilized ultrasonic amplitude was set at 1.25 µm in the first two experiment and 800 nm in experiment 3. The choice of two consecutive presentations of an identical signal as in [10] was made to enable a more reliable psychometric analysis in experiment 1 as well as to provide more options for the counting task performed in experiment 2. In all experiments, the movement was performed perpendicularly to the nodal lines of the ultrasonic device.…”

Physical Variables Underlying Tactile Stickiness During Fingerpad Detachment

“…We designed an experimental apparatus that can measure contact forces and finger contact area over time to test how these quantities are related to human stickiness perception (see Figure 1). We also measured the moisture of the participant's fingerpad, as moisture tends to change physical interactions between the skin and a surface (Tomlinson et al, 2011;Derler et al, 2015;Dzidek et al, 2017;Gueorguiev et al, 2017). Moreover, we took the comfort of the participants into account by not attaching any fixtures to the finger and by making the finger-glass interaction direction downward.…”

Detection of Static, Dynamic, and No Tactile Friction Based on Non-linear dynamics of EEG Signals: A Preliminary Study

“…Due to the collision of the skin with a surface, tactile friction is formed between the skin and the surface. The frictional interaction between the skin and the surface influences the tactile perception [1,2]. Indeed, the level of friction or the degree of roughness affects the characteristics of this perception [3] and, consequently, the brain state [4].…”

“…The main goals of this study is (1) to explore how the brain dynamics (linear and non-linear features) change in response to a sequence of events: touching a surface without moving the skin (sensation of a static friction), pulling the skin along the surface in the direct passive way (sensation of a dynamic friction), and disconnecting the skin from the surface (sensation of no friction), and (2) designing a system that can automatically detect the mentioned three states according to the…”