Blowing in the wind: Perceiving structure in trees and bushes

When lights are mounted at the ends of the limbs of a tree and the surround darkened such that branches and trunk are not visible, viewers can nonetheless make systematic and precise judgments about the unseen structure of the tree through its motion. They seem to perform this task by picking up information about the relative arborization of the tree through the vector paths of the lights on the limbs. Theoretically speaking, the focus of this study is on the perception of second-order centers of moment; previous studies have focused on the perception of first-order centers. A second-order center in a tree-like structure is the location where limb meets trunk, and it is these that perceivers can infer from the dynamic display. The importance of this study is to demonstrate further that the study of centers of moment makes possible a detailed and differential study of event perception.     

The minimum principle and the perception of absolute,common, and relative motions

Wheel-generated motions have served as a touchstone for discussion of the perception of wholes and parts since the beginning of Gestalt psychology. The reason is that perceived common motions of the whole and the perceived relative motions of the parts are not obviously found in the absolute motion paths of points on a rolling wheel. In general, two types of theories have been proposed as to how common and relative motions are derived from absolute motions: one is that the common motions are extracted from the display first, leaving relative motions as the residual; the other is that relative motions are extracted first leaving common motions as the residual. A minimum principle can be used to defend both positions, but application of the principle seems contingent on the particular class of stimuli chosen. We propose a third view. It seems that there are at least two simultaneous processes—one for common motions and one for relative motions—involved in the perception of these and other stimuli and that a minimum principle is involved in both. However, for stimuli in many domains the minimization of relative motion dominates the perception. In general, we propose that any given stimulus can be organized to minimize the complexity of either its common motions or its relative motions; that which component is minimized depends on which of two processes reaches completion first (that for common or that for relative motions); and that the similarity of any two displays depends on whether common or relative motions are minimized.