Movement, Psychology of

This study tested the hypothesis that the perception of 2-flash apparent motion (points of light are briefly presented in succession at a nearby locations) is the outcome of competition between two opposing motion directions activated by the stimulus. Experiment 1 replicated previous results obtained using 2-flash stimuli; motion was optimal for a non-zero inter-frame interval (Kolers, 1972; Wertheimer, 1912). In Experiment 2, stimuli were pared down to a single luminance change toward the background at one location, and a single luminance change away from the background at one location at another. Results were consistent with apparent motion being specified by the counter-changing luminance; motion was optimal for a non-zero inter-frame interval. A subtractive model based on counter-change stimulating opposing motion directions did not account for the results of the 2-flash experiment. An alternative model based on the combined transient responses of biphasic detectors is discussed.

The dynamics of recruitment and suppression processes are studied in the coupled pendulum paradigm developed by Kugler and Turvey (1987). Experimentally, the main concern is whether pendulum motion in this task is purely planar. Theoretically, the main concern is whether one-dimensional phase equations developed originally by Haken, Kelso and Bunz (1985) and the symmetry breaking extension by Kelso, Delcolle and Schoner (1990), can capture the richness of the dynamics of this experimental model system. In experiment 1, subjects swung single hand-held pendulums in time with an auditory metronome whose frequency increased. Bifurcations from planar to spherical pendulum motion occurred at critical cycling frequencies. Typically, these frequencies were above the pendulum's eigenfrequency. Spectral measures showed that spherical pendulum motion was generated through the recruitment of wrist abduction and adduction. The spectral measures revealed that elbow flexion and extension was recruited as movement rate increased, presumably to stabilize pendulum motion. When recruited, both components frequency- and phase-entrained with the primary pendulum mover, wrist ulnar flexion-extension. In experiment 2, subjects swung coupled pendulums in either an in-phase or anti-phase coordinative mode as movement rate increased. Transitions between coordinative modes were not observed. Pattern stability, as defined by the variability of the phase relation between the pendulums, was not affected to any large degree by increasing movement rate. Bifurcations from planar to spherical motion emerged at critical cycling frequencies. Spectral measures demonstrated that this motion was generated by abduction and adduction of the wrist. Elbow flexion-extension motion was also recruited. The newly active components frequency- and phase-entrained with wrist ulnar flexion-extension. When the same neuromuscular components were recruited simultaneously, e.g., elbow motion in both arms, the components exhibited frequency- and phase-entrainment with the task defined pattern. The results demonstrate that recruitment processes stabilize the coordinative modes, thereby reducing the need to switch patterns. Both experiments revealed a much richer dynamics than ever observed in the coupled pendulum paradigm and question the application of one-dimensional phase equation models to the coupled pendulum paradigm.

It has been argued that the perception of apparent motion is based on the detection of counterchange (oppositely signed changes in luminance contrast at pairs of spatial locations) rather than motion energy (spatiotemporal changes in luminance). A constraint in furthering this distinction is that both counterchange and motion energy are present for most motion stimuli. Three experiments used illusory-contour and luminance-based stimuli to segregate (experiments 1 and 2) and combine (experiment 3) counterchange and motion energy information. Motion specified by counterchange was perceived for translating illusory squares over a wide range of frame durations, and preferentially for short motion paths. Motion specified by motion energy was diminished by relatively long frame durations, but was not affected by the length of the motion path. Results for the combined stimulus were consistent with counterchange as the basis for apparent motion perception, despite the presence of motion energy.