Open-source instrumented object to study dexterous object manipulation

Córdova Bulens, David [University College Dublin, Dublin, Ireland] du Bois de Dunilac, Sophie [University College Dublin, Dublin, Ireland] Delhaye, Benoit [UCL] Lefèvre, Philippe [UCL] Redmond, Stephen J. [University College Dublin, Dublin, Ireland]

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 device’s 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 object’s 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 statement In 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 object’s 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.