Heavy-tailed distributions in haptic perception of wielded rods

Humans identify properties (e.g., the length or weight) of objects through touch using somatosensory perceptions in the limbs. Humans identify these properties by manipulating an object to access its inertial qualities. However, there is little work evidencing a unifying pattern of movements humans use to access these inertial properties. The current study examined if participants’ wielding movements followed a systematic distribution—specifically, a Lévy-like distribution that is characterized by heavy-tails and is often seen in efficient foraging behavior. Participants wielded rods they could not see and were tasked to identify whether the rod they were wielding was the longer or shorter of two rods. While participants wielded the rod, the rod’s motion was captured. Results demonstrate that the sampling of angular accelerations produced heavy-tailed distributions. Since angular acceleration has a distinct physical–mathematical relationship with inertia, this finding is consistent with the interpretation that the haptic subsystems are sensitive to the inertial properties of an object. Angular acceleration from wielding motions appear to follow a similar distribution as optimal foraging strategies—perhaps it is the case that humans are foraging for information about the inertia of an object through changes in angular acceleration and wielding movements.