Academic journal article Attention, Perception and Psychophysics

Field-Like Interactions between Motion-Based Reference Frames

Academic journal article Attention, Perception and Psychophysics

Field-Like Interactions between Motion-Based Reference Frames

Article excerpt

Published online: 17 April 2015

© The Psychonomic Society, Inc. 2015

Abstract A reference frame is required to specify how motion is perceived. For example, the motion of part of an object is usually perceived relative to the motion of the object itself. Johansson (Psychological Research, 38, 379-393, 1976) proposed that the perceptual system carries out a vector decomposition, which rewsults in common and relative motion percepts. Because vector decomposition is an ill-posed problem, several studies have introduced constraints by means of which the number of solutions can be substantially reduced. Here, we have adopted an alternative approach and studied how, rather than why, a subset of solutions is selected by the visual system. We propose that each retinotopic motion vector creates a reference-frame field in the retinotopic space, and that the fields created by different motion vectors interact in order to determine a motion vector that will serve as the reference frame at a given point and time in space. To test this theory, we performed a set of psychophysical experiments. The field-like influence of motion-based reference frames was manifested by increased nonspatiotopic percepts of the backward motion of a target square with decreasing distance from a drifting grating. We then sought to determine whether these field-like effects of motion-based reference frames can also be extended to stationary landmarks. The results suggest that reference-field interactions occur only between motion-generated fields. Finally, we investigated whether and how different reference fields interact with each other, and found that different reference-field interactions are nonlinear and depend on how the motion vectors are grouped. These findings are discussed from the perspective of the reference-frame metric field (RFMF) theory, according to which perceptual grouping operations play a central and essential role in determining the prevailing reference frames.

Keywords 2-D motion · Motion integration · Temporal processing

The relativity of perceived motion

By definition, motion is a change of position over time. Hence, the definition implies that to determine motion, one needs to have references (or coordinate systems) for position and time, and motion becomes relative to these coordinate systems. The choice of the coordinate systems and their scales depend on the phenomena of interest. For example, astronomical scales are used to characterize planetary motions, and the orbital speed of earth's motion according to a solar reference frame is about 30 km/s. However, in our ecological environment, for all practical purposes the earth appears stationary, and an earth-based (geocentric) reference frame prevails. As a result, explicitly or implicitly, geocentric (also called spatiotopic) motion is generally regarded as the "real,""physical," or Babsolute^ motion, whereas motion relative to other reference frames is considered Brelative^ or Billusory^ motion (Swanston, Wade, & Day, 1987; Wade & Swanston, 1987). However, in analyzing its inputs, our visual system is faced by the complexity that arises at the individual stimuli level, and perceptual organizational principles, such as Gestalt grouping and figure-ground segregation are proposed to be fundamental requirements in processing visual inputs (Koffka, 1935; Wagemans, Elder, et al., 2012; Wagemans, Feldman, et al., 2012). The perception of a stimulus does not only depend on its own individual properties but also on the properties of other spatiotemporally neighboring stimuli (Koffka, 1935). It is not surprising, then, that relative motion was a central topic in Gestalt psychology (Duncker, 1929; Ellis, 1938). In one of his experiments, Karl Duncker used displays generated by point-lights attached to an otherwise invisible rotating and translating circular piece of cardboard (Duncker, 1929,p. 240). He found that when a single point-light was attached to the rim of the cardboard, observers reported seeing the point-light moving along a cycloidal trajectory. …

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