Grasping follows Weber’s law: How to use response variability as a proxy for JND

Abstract

Weber’s law is one of the most fundamental psychophysical principles. It relates JND to stimulus magnitude and therefore makes a statement at the level of the physical stimuli. Studies reporting a violation of Weber’s law for grasping used SDMGA as proxy for JND and therefore forsook the stimulus level. We showed that this is problematic when the response function is nonlinear (as in grasping) and that instead JND must be calculated, which brings us back to the stimulus level. If we do this, then grasping followsWeber’s law—in our own data, as well as in previous studies that claimed a violation of Weber’s law for grasping. Our method is general and can also be used in other tasks and sensory domains whenever a direct assessment of JND is not possible