Abstract
The purpose of our study was to investigate the effect of grouping on visual working memory using a change-detection task. In Experiment 1, we presented the sample display with either 2, 4 or 6 colored circles for 100 ms, followed by a blank period of 900 ms, and the test display until response. Two circles were connected by a line in the grouped condition while a line was merely presented between two circles without connection in the non-grouped condition. Participants' task was to detect the color change between the sample and the test display. The color was changed only for one circle and for the 50% of trials. To report changes, participants had to press the left mouse button and indicate the location of the change. They reported no change by pressing the right mouse button. When we calculated the correctness in detection of color changes regardless of the correctness in locations, performance in the grouped condition did not significantly differ from the non-grouped condition. However, when we computed the correctness based on both color changes and locations, performance in the non-grouped condition was significantly better than in the grouped condition. If the visual system treated a grouped item as an object, changes in the grouped condition would have been less salient because only part of the object changed its color in this condition. We tested this hypothesis in Experiment 2. The potential location of changes was designated by presenting only one pair (grouped or non-grouped) at test display. When participants knew the potential location of changes, their performance in the grouped condition did not significantly differ from that in the non-grouped condition. Our findings suggested that grouped items were treated as objects in visual working memory and this grouping effect paradoxically caused the reduction of working memory capacity.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(2009-0089090).