Abstract
Ensemble coding is a mode of our visual system in which summary statistics like average size can be extracted from a group of multiple objects. Although ensemble coding is basically very accurate, it becomes less accurate when irrelevant stimuli are mixed in with the group of interest. A previous study indicated that when an array of variously sized circles of two colors, relevant and irrelevant ones, were presented simultaneously, the perceived average size of the relevant stimuli was affected by the average of the irrelevant stimuli, indicating that it is hard to ignore salient stimuli (Nakada & Murakami, VSS2020). In the present study, we presented variously sized circles of two colors sequentially at the same location and investigated whether observers could pick up only the relevant stimuli to extract their average size. We used the “rapid serial visual presentation (RSVP)” method to present the colored circles. Observers, who were to focus only the blue circles, were presented with two groups of circles in sequence. The first group also contained green circles, whose average was chosen from three values (less than, equal to, and greater than the average of the blue circles). They would differently affect the perceived average size of the blue circles if ensemble coding was affected by irrelevant stimuli. However, when the average of the green circles was greater than that of the blue circles, the perceived average size did not change. On the other hand, when the average of the green circles was less than or equal to that of the blue circles, the perceived average size became smaller. Ensemble coding is known to extract the salient elements of the group, but we found that in successive presentation, irrelevant stimuli of larger sizes are eliminated, although it is still hard to completely ignore other irrelevant stimuli.