The influence of temporal offset noise on the perception of possible versus impossible movement

Abstract

Humans appear extremely sensitive to various aspects of biological motion. In this research we investigated how introducing temporal offset noise into different joint segments influenced the perception of human movement. We presented two types of movements — a point-light arm movement and a stick figure ballet dancer. For the arm movements we began with 3D recordings sampled at 60 Hz of the head, shoulder, elbow, wrist and hand of human actors while they drew circles on a board. Next, we introduced various levels of temporal offset between the motion of the elbow and the other points to create displays with increasing noise levels. The duration of the arm movement stimuli varied between 4 and 6.5 sec. For the ballet movements we began with 3D whole-body recordings sampled at 60 Hz of different ballet movements that were transformed into a hierarchical joint angle representation of the movement. Then, we introduced random temporal offsets into all the joint angles to create displays where the coordination among the joints was disrupted. By varying the average value of temporal offset we were able to create displays with increasing noise levels. Movement duration of the ballet stimuli was fixed at 3 sec. During the experimental phase, we displayed the movements as quicktime movies to naïve observers and asked them to judge whether a movement was possible or not by rating it on 9 point scale that varied from definitely possible to definitely impossible. Results showed that the observers were sensitive to the temporal offset noise in judging possible versus impossible movements presented by the human arm. However, they were less sensitive when they were presented the whole-body ballet movements. The results suggested that the perception of human movement is influenced by the different temporal offset noise as well as by the level of complexity of the observed human action.

EC grant RTN2-2001-00107, Royal Society UK-Korea Joint Project Grant