The length perception via dynamic touch with undefined inertia

Abstract

Perception of object length arising from manual wielding is powerfully influenced by the inertia tensor of wielded objects (e.g., Solomon & Turvey, 1988). In solid objects the inertia tensor is a fixed quantity which can be computed, and whose responses to torques are stable. By contrast, when I lift a glass to drink, I am wielding (in addition to the glass) a liquid, whose dynamics (including the inertia tensor) vary as a function of movement. In this study I asked whether judgments of object length during manual wielding would be influenced by the presence of liquid mass in the wielded object. In Experiment 1, the type of weight was manipulated (liquid and solid weights). In Experiment 2, I manipulated the type of weight and movement of liquid by orienting the cylindrical weight horizontally or vertically. In both experiments, judgments of length were strongly correlated with the weight position, and changing dynamics of liquid weights did not reduce the accuracy of length perception. On the basis of these results I argue that the inertia tensor is not likely single unique mechanical information to be detected for the haptic length perception.