Force Feedback is Noticeably Different for Linear versus Nonlinear Elastic Tissue Models

Realistic modeling of the interaction between surgical instruments and human organs has been recognized as a key requirement in the development of high-fidelity surgical simulators. Primarily due to computational considerations, most of the past simulation research within the haptics community has assumed linear elastic behavior for modeling tissues, even though human soft tissues generally possess nonlinear viscoelastic properties. Hence, this paper quantitatively compares linear and nonlinear elasticity-based models. It is demonstrated that, for a nonlinear model, the well-known Poynting effect developed during shearing of the tissue results in normal forces not seen in a linear elastic model. The difference in force magnitude and force direction for linear and nonlinear models are larger than the just noticeable difference for contact force and force-direction discrimination thresholds published in the psychophysics literature, respectively. This work applies a proposed framework for examining the effect of tool-tissue interaction modeling techniques on human perception of surgical simulators with haptic feedback