Perceptually averaging in a continuous visual world: extracting statistical summary representations over time.

Beyond processing individual features and objects, the visual system can also efficiently summarize scenes--for example, allowing observers to perceive the average size of a group of objects. Extraction of such statistical summary representations (SSRs) is fast and accurate, but researchers do not yet have a clear picture of the circumstances in which they operate. Previous studies have always used discrete input--either spatial arrays of shapes or temporal sequences of shapes presented one at a time. Real-world environments, in contrast, are intrinsically continuous and dynamic. We investigated the ability to compute average size in displays of objects (or sometimes a single object) that changed continuously, expanding and contracting over time. The results indicated that perceptual averaging can operate continuously in dynamic displays--sampling multiple times during a single continuous transformation with no discrete boundaries. Moreover, some dynamic changes (expansion) influence the resulting perceptual averages more than others (contraction), perhaps because of attentional capture. These results collectively illustrate how SSRs may be well adapted to dynamically changing real-world environments.