Biology subjects

Wiertlewski, M.

Publications and source records attributed to Wiertlewski, M..

3 recordsLinked to original sources

bioRxiv2026

Adhesion or Vibration? Frequency-Dependent Fingertip Contact on Electrostatic Displays

Electrostatic actuation enables programmable tactile feedback by modulating finger-surface friction via oscillating electric fields. Despite its potential, widespread adoption is hindered by an incomplete understanding of the underlying physical mechanisms, particularly the dynamics of finger-surface contact. To address this problem, this study presents the first time-resolved measurements of real contact area modulation under electrostatic actuation, obtained concurrently with contact forces. Experiments with ten participants sliding their fingers on an electrostatic display revealed an inverted U-shaped dependence of mean contact area and tangential force on actuation frequency, with a pronounced peak near 116 Hz--consistent with the frequency-dependent response of the fingertip-display system captured by mass-spring-damper and contact models. Two regimes emerged: a vibration regime below 320 Hz, where the voltage increased the contact area more than the tangential force, thereby reducing interfacial shear stress relative to the baseline; and an adhesion regime at higher frequencies, where skin viscoelasticity attenuated oscillations and restored or increased shear stress. For moist fingers, vibration effects were reduced, weakening the modulation of both tangential force and contact area. These findings reveal how adhesion and vibration jointly govern finger-surface interactions, guiding the design of next-generation electrostatic haptic interfaces.

biophysics↗

bioRxiv2023

Role of finger movement kinematics in friction perception at initial contact with smooth surfaces

When manipulating objects, humans adjust grip force to friction remarkably quickly: it may take just 100 ms to see adjustment to friction at the skin-object interface. While the motor commands adapt, subjects become aware of slipperiness of touched surfaces. In this study, we explore the sensory processes underlying such friction perception when no intentional exploratory sliding movements are present. Previously, we have demonstrated that humans cannot perceive frictional differences when surfaces are brought in contact with an immobilized finger (Khamis et al., 2021b) unless there is a submillimeter lateral displacement (Afzal et al., 2022), or subjects made the movement themselves (Willemet et al., 2021). In the current study, subjects actively interacted with a device that can modulate friction using ultrasound, without an exploratory sliding movement, as they would when gripping an object to lift it. Using a two-alternative forced-choice paradigm, subjects had to indicate which of two surfaces felt more slippery. Subjects could correctly identify the more slippery surface in 87 {+/-} 8% of cases (mean{+/-}SD; n=12). Biomechanical analysis of finger pad skin contacting a flat smooth surface indicated that natural movement kinematics (e.g., tangential movement jitter and physiological tremor) may enhance perception of frictional effects. To test whether this is the case, in a second experiment a hand support was introduced to limit fingertip movement deviation from a straight path. Subject performance significantly decreased (66 {+/-} 12% correct, mean{+/-}SD; n=12), indicating that friction perception at the initial contact is enhanced or enabled by natural movement kinematics. Significance statementSensing surface friction is crucial for automatic grip force control to avoid dropping objects. A slipping handhold can lead to loss of balance and falling. In many instances, the required grip force may exceed hands physical ability or an objects breakage point, therefore cognitive selection of a safe and achievable action plan based on friction perception is critical. Little is known about how our awareness of surface slipperiness is obtained under such circumstances without exploratory movement. The current study demonstrates that natural movement kinematics inducing submillimeter lateral movements play a central enabling role, demonstrating interdependence between the motor system and sensory mechanisms. These findings broaden our fundamental understanding of sensorimotor control and could inform the development of advanced sensor technologies.

neuroscience↗

bioRxiv2021

Initial contact shapes the perception of friction

Humans efficiently estimate the grip force necessary to lift a variety of objects, including slippery ones. The regulation of grip force starts with the initial contact, and takes into account the surface properties, such as friction. This estimation of the frictional strength has been shown to depend critically on cutaneous information. However, the physical and perceptual mechanism that provides such early tactile information remains elusive. In this study, we developed a friction-modulation apparatus to elucidate the effects of the frictional properties of objects during initial contact. We found a correlation between participants conscious perception of friction and radial strain patterns of skin deformation. The results provide insights into the tactile cues made available by contact mechanics to the sensorimotor regulation of grip, as well as to the conscious perception of the frictional properties of an object.

biophysics↗