Hierarchical motion organization in random dot configurations.

Abstract

Motion organization has 2 aspects: the extraction of a (moving) frame of reference and the hierarchical organization of moving elements within the reference frame. Using a discrimination of relative motions task, the authors found large differences between different types of motion (translation, divergence, and rotation) in the degree to which each can serve as a moving frame of reference. Translation and divergence are superior to rotation. There are, however, situations in which rotation can serve as a reference frame. This is due to the presence of a second factor, structural invariants (Sis). Sis are spatial relationships persisting among the elements within a configuration such as a collinearity among points or one point coinciding with the center of rotation for another (invariant radius). The combined effect of these 2 factors-motion type and Sis-influences perceptual motion organization.An event is the natural unit of analysis for perception. An event is an actor or object that displays a behavior against a background, such as a falling object, the changing color of a traffic light, or the locomotion of an organism in the environment. In the case of motion, the background is the event's frame of reference, a coordinate system that may, itself, be moving. Because the motion of an element is defined relative to its reference frame, the element also shares the motion of the frame, and thus motion organizations are hierarchical.Hierarchical motion organizations are inherently ambiguous. Every motion affords an infinite number of different descriptions as a consequence of the choice of different moving coordinate systems, or frames of reference. Consider the motion of our planet. Common sense and medieval astronomy take the earth as the frame of reference for all motions: the flowing of a river; the locomotion of an animal; or the motion of the sun, moon, planets, and stars. Contemporary astronomy, on the other hand, takes the sun as a moving frame of reference. Within this reference frame, the earth is described as revolving around the sun, and the moon is described as having two kinds of motion, one around the earth and a second one, common to the earth, around the sun. This newer description of the solar system is no more true in a geometrical sense than the earth-centered one. From the point of view of providing an accurate description, any frame of reference is as good as any other. However, the use of the sun as a frame of reference for the earth and of the earth as a frame of reference for the moon promotes a better mechanistic description of this dynamical system.The perceptual system is adept at finding useful organizations for the motions that it encounters. When observing events, people correctly identify the motions of an object (where it is going) and motions within the object (what it is doing). The first are called common motions because they are common to the constellation of elements or features of the object. The second are called relative motions, implying that they are hierarchically orga...

Updating space during imagined self- and array translations

“…Research in a number of domains has suggested that perceiving, remembering, and updating may be different for translation versus rotation (Bertamini & Proffitt, 2000;Chance, Gaunet, Beall, & Loomis, 1998;Presson & Montello, 1994;Price & Gilden, 2000;Rieser, 1989). Decrements in performance have been shown to result when tasks involve rotational in comparison with translational movements.…”

“…Distinctions between rotations and translations have also been seen in other cognitive domains. For example, in a perceptual organization task, translation served as a moving frame of reference more easily than rotation (Bertamini & Proffitt, 2000). In a task of memory for motion, humans remembered the direction of translational movement better than that of rotational movement (Price & Gilden, 2000).…”

Perceptual Guidelines for Creating Rectangular Treemaps

“…We also hypothesized that judgments of rectangles with different primary orientations (horizontal or vertical) would result in increased error. This hypothesis is based in part on prior perceptual research [7] which suggests that mental rotation is more cognitively demanding than either translation or scaling.…”

Form features provide a cue to the angular velocity of rotating objects.

“…Such size invariance requires the integration of local velocity estimates with their distance from the center of rotation (Bertamini & Proffit, 2000; Porter et al, 2011). Relative to the rest of the object, the center of rotation is the one point on the object that is not moving, a fact that may provide some clue to the visual system as to its location (Bertamini & Proffit, 2000). The importance of correctly identifying the center of rotation is highlighted by the fact that when the center of rotation is misperceived, predictable errors in perceived speed are made (Barraza & Grzywacz, 2003).…”