Underestimation of numerosity in dynamic visual display
16.515, Friday, May 10, 5:30 - 8:00 pm, Vista Ballroom
Ricky K. C. Au1,2, Katsumi Watanabe1; 1Research Center for Advanced Science and Technology, The University of Tokyo, 2Japan Society for the Promotion of Science
Previous research suggested that the estimation of numerosity of a large number of objects is possible even with a short presentation of static visual display. The present study examined the estimation of numerosity of objects presented in a sequence and whether it would be modulated by the availability of attentional resources. In Experiment 1, two streams of events (each 960 ms) showing dots of the same shape and size were presented in each trial. In one stream, two dots of different colors (red and green) were presented at random locations on an imaginary ring in each frame (40 ms) of a stream, resulting in 24 frames. In the other stream, either one, two or three dots of the same color (red or green), varied across a range of "percentage of frames with one (or three) dots", were presented in each frame. Observers were asked to judge which of the streams contained a greater number of dots. The results showed that the observers judged the stream with same-color dots contained a less number of dots than the different-color stream. This difference disappeared when a slow presentation speed (240 ms/frame) and static visual displays were used. In Experiment 2, observers performed a dual-task in each trial: numerosity judgment task and target detection task with different levels of attentional load (number of targets to be reported). The data revealed that the task difficulty of the dual-task has a remarkable influence on how precisely the observers performed the numerosity judgment task, but the underestimation effect associated with the same-color stimuli remained evident even in the dual-task conditions. These results suggest that identical objects presented in succession might induce substitution among themselves, leading to a perception of being less numerous overall; and that exploiting the availability of attentional resources does not eliminate this underestimation effect.