Abstract
Smooth apparent motion is often perceived between two stimuli when they are presented at appropriate temporal and spatial separations even when they differ substantially in appearance (for example in size). In contrast, when a moving stimulus undergoes an abrupt change in size, it is perceived as two simultaneously present objects, one of the changed size and one of the original size. This change-related persistence occurs, we have argued, because the change disrupts the original object representation causing the establishment of a second one to accommodate the change (Moore, Mordkoff, & Enns, 2007). Together these observations present a quandary with regard to inferring represented scene organization from phenomenological reports. For apparent motion, a two-stimulus event appears to be represented as a scene that is comprised of one object. In contrast, for change-related persistence, a one-stimulus event appears to be represented as a scene that is comprised of two objects. We created displays in which a single disc was displaced horizontally in 3° steps, for 80 ms at each location, separated by variable interstimulus intervals (ISI). The size of the disc in the second to last frame of the sequence varied from 10% to 100% the size of the original disc. Some observers reported whether they perceived smooth motion in the final two frames of the display or not. Other observers reported how many objects they perceived in the final two frames of the display, one or two. Good motion was reported at appropriate ISIs regardless of size change, suggesting a scene organization of one object. In contrast, two objects were reported more often with larger size changes, suggesting a change in scene organization from one object to two. Implications for the use of perceived motion as proxy for “represented as a single object” are explored.
Supported by NIH grant MH067793 to C. M. Moore.