Abstract
Common fate is a fundamental law of Gestalt psychology: elements that move together are perceived as being part of the same object (Wertheimer, 1923). Although common fate suggests that the perception of motion drives object perception, the spatial arrangement of the elements also can have an effect on the perception of motion, even when that arrangement is perceived only via motion. For example, Uttal et al. (2000) showed that dots that moved in a common direction within a cloud of randomly moving dots were detected better when the target dots were arranged collinearily than when they were non-collinear. These results indicate that both motion direction and spatial organization are crucial for target detection in random dot motion displays.
As we age, some aspects of our motion perception remain relatively unchanged, while other aspects are impaired. For example, the ability to integrate form and motion information in the context of higher-level visual stimuli, such as biological motion stimuli, seems to be impaired (Pilz et al., in press). Here, we investigated the effect of aging on the perception of common fate, and the way common fate interacts with form perception.
In the current experiment, older (∼65 years) and younger (∼ 23 years) subjects detected a group (collinear or non-collinear) of four coherently moving dots that appeared in one of two sequentially presented sets of randomly moving dots with limited lifetime. The target dots always moved in a common direction, which varied across trials. Compared to younger subjects, older subjects showed a general decline in target detection based on common fate. This decline was significantly greater for non-collinear targets. These results indicate that with aging, form regularity is especially important for detecting coherently moving targets, which may underlie previous results regarding perception in higher-level visual tasks such as biological motion.
The current research was supported by the Alexander von Humboldt Foundation (KSP), the Alexander Graham Bell Canada Graduate Scholarship(ER), and the and the Canadian Institutes of Health Research (ASB and PJB).