The role of friction on skin wetness perception during dynamic interactions between the human index finger pad and materials of varying moisture content

Abstract

Mechanosensory inputs arising from dynamic interactions between the skin and moisture, such as when sliding a finger over a wet substrate, contribute to the perception of skin wetness. Yet, the exact relationship between the mechanical properties of a wet substrate, such as friction, and the resulting wetness perception, remains to be established under naturalistic haptic interactions. We modelled the relationship between mechanical and thermal properties of substrates varying in moisture levels (0.49x10-4; 1.10x10-4; 2.67x10-4 ml mm-2), coefficient of friction (0.783, 0.848, 1.033, 0.839, 0.876, 0.763), and maximum thermal transfer rate (Qmax, ranging from 511 to 1260 W m-2 K-1), and wetness perception arising from the index finger pad's contact with such substrates. Forty young participants (20M/20F) performed dynamic interactions with 21 different stimuli using their index finger pad at a controlled angle, pressure, and speed. Participants rated their wetness perception using a 100 mm visual analogue scale (very dry to very wet). Partial least squares regression analysis indicated that coefficient of friction explained only ~11% of the variance in wetness perception, while Qmax and moisture content accounted for ~22% and 18% of the variance, respectively. These parameters shared positive relationships with wetness perception, such that the greater the Qmax, moisture content, and coefficient of friction, the wetter the perception experienced. We found no differences in wetness perception between males and females. Our findings indicate that while the friction of a wet substrate modulates wetness perception, it is still secondary to thermal parameters such as Qmax.

Remapping Wetness Perception in Upper Limb Amputees

“…One possibility might be that they relied more strongly than the other participants on the multisensory integration of mechanical cues (when combined with thermal cues) to detect wetness. [ 10,14 ] We have recently observed a similar phenomenon when comparing wetness perception between younger and older adults, whereby the latter group presented reduced wetness sensitivity in the presence of intact thermal sensitivity. [ 15 ] We hypothesized that age‐induced changes in tactile sensitivity might underlie differences in wetness perception in the absence of a thermal effect, a mechanism that could also underlie the outcomes observed in the nonresponders of the current study.…”

“…[ 9 ] In fact, mechanical parameters, such as friction, have been shown to play a secondary role in wetness perception when compared to the principal contribution of thermal factors. [ 10 ] Building on this observation, it has been demonstrated that touching a cold, dry object can generate a wetness illusion. [ 7,9 ] Our goal is to use this illusory perception to mediate wetness sensation from the prosthetic hand to an intact part of the body (e.g., the upper arm).…”

“…[9] In fact, mechanical parameters, such as friction, have been shown to play a secondary role in wetness perception when compared to the principal contribution of thermal factors. [10] Building on this observation, it has been demonstrated that touching a cold, dry object can generate a wetness…”

Thermal modulation of skin friction at the fingertip

“…The participant was required to maintain a stable 5N normal force during the pulling action, using visual feedback from the digital meter described above. Normal and tangential forces were used to calculate the coefficient of kinetic friction (CoF) [14] and were averaged every 0.33s during each sliding movement. The data was analysed for the independent and interactive effects of plate temperature (3 levels: 24, 16, or 38ºC) and time (10 levels: 0 to 0.33s) by means of a 2-way repeated measure ANOVA.…”

Comparison of reality and illusion of wetness on soft materials and the multisensory perceptual space of wetness illusion

“…When considering contact between the skin and soft materials, which exhibit varying thickness and roughness, parameters such as stickiness and softness play a more significant role. 8,9 In particular, an increase in the softness of dry cloth has been shown to intensify wetness perception. 10,11 Nevertheless, these studies have been limited to static contact and have not explored the influence of surface properties of the soft material.…”