A viscoelastic model of the human fingerpad and a holistic model of human touch

author:Diane Tanya Victoria Pawluk
adviser:Robert D. Howe
degree: Ph.D.
institution: Harvard University

The main intent of this thesis is to develop an engineering model describing the response of the human peripheral tactile system when an object dynamically contacts the fingerpad. In developing such a model, it is only possible to measure the system at two points: mechanically at the surface of the skin and neurophysiologically as the resulting nerve signal heads toward the brain. We first consider the dynamic mechanical interaction between the fingerpad and a prototypical object (i.e., a flat indentor) applied normal to the fingerpad. Experimentally we applied controlled position trajectories to the fingerpad and measured the resulting force and spatially distributed pressure response. We will show that these experimental results can be explained by an analytical model consisting of a quasi-linear viscoelastic model of tissue combined with a Hertzian contact model. The contact mechanics also create stresses and strains within the tissue, which are then transduced through the mechano-electrical components of the peripheral mechanoreceptive units, resulting in a nerve fiber response. We have, in addition, considered the transmission of the signal through these components by developing a '1-D' model which relates the input applied to the surface of the skin to the resulting nerve fiber response. Using existing neurophysiological data, we have shown that the response of the mechanoreceptive units to '1-D' stimuli can be modeled by simple linear mechanical components combined with the Hodgkin-Huxley equations.

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