An individual's skin stiffness predicts their tactile acuity

Abstract

Individual differences in tactile acuity have been correlated with age, gender, and finger size, while the role of the skins stiffness has been underexplored. Using an approach to image the 3- D deformation of the skin surface while in contact with transparent elastic objects, we evaluate a cohort of 40 young participants, who present a diverse range of finger size, skin stiffness, and fingerprint ridge breadth. The results indicate that skin stiffness generally correlates with finger size, although individuals with relatively softer skin can better discriminate compliant objects. Analysis of contact at the skin surface reveals that softer skin generates more prominent patterns of deformation, in particular greater rates of change in contact area, which correlate with higher rates of perceptual discrimination, regardless of finger size. Moreover, upon applying hyaluronic acid to soften individuals skin, we observe immediate, marked and systematic changes in skin deformation and consequent improvements in perceptual acuity. Together, the combination of 3- D imaging of the skin surface, biomechanics measurements, multivariate regression and clustering, and psychophysical experiments show that subtle distinctions in skin stiffness modulate the mechanical signaling of touch and shape individual differences in perceptual acuity. Key points described in the manuscriptO_LIWhile declines in tactile acuity with aging are a function of multiple factors, for younger people the current working hypothesis has been that smaller fingers are better at informing perceptual discrimination due to a higher density of neural afferents. C_LIO_LITo decouple relative impacts on tactile acuity of skin properties of finger size, skin stiffness, and fingerprint ridge breadth, we combined 3D imaging of skin surface deformation, biomechanical measurements, multivariate regression and clustering, and psychophysics. C_LIO_LIThe results indicate skin stiffness generally correlates with finger size, although more robustly correlates with and predicts an individuals perceptual acuity. C_LIO_LIIn particular, more elastic skin generates higher rates of deformation, which correlate with perceptual discrimination, shown most dramatically by softening each participants skin with hyaluronic acid. C_LIO_LIIn refining the current working hypothesis, we show the skins stiffness strongly shapes the signaling of touch and modulates individual differences in perceptual acuity. C_LI