Biology subjects

Delhaye, B.

Publications and source records attributed to Delhaye, B..

3 recordsLinked to original sources

bioRxiv2023

Open-source instrumented object to study dexterous object manipulation

Humans use tactile feedback to perform skillful manipulation. When tactile sensory feedback is unavailable, for instance, if the fingers are anesthetized, dexterity is severely impaired. Imaging the deformation of the finger pad skin when in contact with a transparent plate provides information about the tactile feedback received by the central nervous system. Indeed, skin deformations are transduced into neural signals by the mechanoreceptors of the finger pad skin. Understanding how this feedback is used for active object manipulation would improve our understanding of human dexterity. In this paper, we present a new device for imaging the skin of the finger pad of one finger during manipulation performed with a precision grip. The devices weight (300 g) makes it easy to use during unconstrained dexterous manipulation. Using this device, we reproduced the experiment performed in Delhaye et al. 2021a. We extracted the strains aligned with the objects movement, i.e., the vertical strains in the ulnar and radial parts of the fingerpad, to see how correlated they were with the grip force (GF) adaptation. Interestingly, parts of our results differed from those in Delhaye et al. 2021a due to weight and inertia differences between the devices, with average GF across participants differing significantly. Our results highlight a large variability in the behavior of the skin across participants, with generally low correlations between strain and GF adjustments, suggesting that skin deformations are not the primary driver of GF adaptation in this manipulation scenario. Significance statementIn this paper, we introduce a new device weighing 300 g and capable of imaging the skin of the finger pad of one finger during manipulation performed with a precision grip. This object is also capable of recording the forces and accelerations applied to the object. We reproduced the experiment performed in Delhaye et al. 2021a using this device. We extracted the strains aligned with the objects movement to analyze how correlated these strains were with GF adaptation. The behavior of the skin across participants presented a large variability, and we observed low correlations between strain and GF adjustments in most participants. Our results suggest that skin deformations are not the primary driver of GF adaptation in this manipulation scenario.

neuroscience↗

bioRxiv2023

Anisotropic Subcutaneous Response During Fingertip Normal and Tangential Loadings

The subcutaneous mechanical response of the fingertip is highly anisotropic due to the presence of a network of collagen fibers linking the outer skin layer to the bone. Yet, the impact of this anisotropy on the fingerpad deformation had not been studied until now. This issue is here tackled using a two-dimensional finite element model of a transverse section of the finger. Different hypotheses about the orientation of the fibers are considered: radial (physiologic), circumferential, and random (isotropic behavior). The three variants of the model are assessed using experimental observations of a finger leaning on a flat surface. Predictions relying on the physiological orientation of fibers align best with reality. Moreover, the orientation of fibers plays a crucial role in determining the distribution of internal strain and stress. These factors, combined with the abrupt shift in contact pressure during the transition from sticking to slipping, represent important sensory cues for partial slip detection. This is valuable information for the development of haptic devices.

bioengineering↗

bioRxiv2023

A haptic illusion created by gravity

Haptic force estimation is a critical aspect of human dexterity. To manipulate objects or interact with a haptic interface successfully, the normal and tangential components of the contact forces produced by our fingertips must be carefully coordinated. The tight coupling between tangential and normal contact forces observed during voluntary movements indicates that the nervous system can estimate these forces with high accuracy. Here, we examined the influence of gravity on manual force production in an isometric task. We trained participants to produce isometric tangential forces with the thumb and index finger on a dynamometer held in precision grip. They were tasked with reproducing these forces in a normal gravitational environment (1 g) and during parabolic maneuvers creating phases of micro- (0 g) and hypergravity (1.6 g). The isometric task results showed that arm weight biases estimation of the forces exerted by the fingertips. Reproduced tangential forces were consistently larger downward than upward in 1 g. This asymmetry was reduced under microgravity and increased under hypergravity. Critically, the normal forces did not reflect this asymmetry, demonstrating that tangential forces were misestimated and pointing to a haptic illusion created by gravity. This gravitational effect on haptic force estimation may have implications for the design of prostheses incorporating force feedback, haptic devices for teleoperations, or haptic supports aimed at improving sensorimotor performance in space.

neuroscience↗