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Wyder-Hodge, Pearson Andrew

University of British Columbia

The mechanical properties of human skin and their relationship to affective touch are investigated. When a surface makes contact with the skin, the soft tissue deforms and, in turn, deforms the mechanoreceptors embedded within. The mechanical factors stimulating hairy skin during pleasant contact are poorly understood. C-Tactile afferents are prevalent in hairy skin and respond to gentle sliding touches. Their firing rate is related to positive affect. In this dissertation, light affective touch is investigated across the arm and torso. A novel velocity-pleasantness model that outperforms the commonly used quadratic model in estimating pleasantness thresholds is proposed. The stroking behaviour that stimulates the C-Tactile afferent system is a dynamic tribological contact. Measures of pleasantness have been correlated to friction in the glabrous skin at the fingertip. The relationship between friction and pleasantness at hairy skin sites is investigated. Measuring friction on the human body is difficult due to the constraints of standard measurement devices (e.g. robotic arms with small staging platforms). Handheld tribometers allow for rapid measurements in hard-to-reach areas. However, the arbitrary orientation of the measurement device relative to the contact normal of the skin can lead to errors in friction measurements. Here, a custom-built handheld tribometer and methods to accurately and reliably measure friction on curved body areas are developed to correct these errors. Sliding skin friction was investigated on the torso. Results show the coefficient of friction, friction load dependence, and soft tissue elasticity vary across anatomical locations. Finally, the tools and techniques developed to measure friction are employed in an experiment to measure affective light touch across the body. Despite the variation in friction due to anatomical area and velocity conditions, no significant effect of friction on pleasantness ratings was observed. Notably, an increase in the spatial frequency of tangent force oscillations led to a marked decrease in pleasantness ratings, suggesting the involvement of afferent systems beyond CT afferents.

Text

2025-02-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90258

Neuroscience

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/