Modeling optimizes the effect of the vertical stripe illusion for foot clearance on upstairs

A fall can result in fractures, sequelae, or even death in the worst-case scenario. Falls often occur because people misjudge step height and do not lift their feet sufficiently. One strategy to combat this issue is the use of vertical stripes to make stairs appear taller than they really are, which can thus prevent underestimation of the real height. However, the appropriate size of the space between the stripes is different for everyone. This study demonstrates how the intensity of an illusion can influence the height of foot clearance when ascending stairs. We validate the feasibility of using a model for determining the striping that can be used to adapt the pattern to individual differences. We constructed the model based on a contrast-sensitivity function using a Gaussian model. In an experiment, we measured the location of the toe via motion capture as participants climbed stairs. As a result, the relationship between foot-clearance and the spatial frequency approximated the function described by the CSF, Contrast Sensitive Function. The coefficients of determination exceeded 0.9 for one participant, 0.8 for two participant and 0.6 for other two participants. We concluded that the model presented CSF would fit the foot clearance with striped stairs for any individual.