Abstract
Although there has been some controversy about whether memory guides attention during visual search, numerous experiments suggest that memory does play some role. For example, Peterson and colleagues (2001) found that when the search task required eye movements, items were rarely reexamined, suggesting that memory can successfully guide search when there are up to 12 items. What is unclear is whether the memory guiding attention is prospective or retrospective in nature. Recently, McCarley and colleagues (2003), using an impoverished task that prevented the planning of scan paths (prospective memory) found that the last 4 items were rarely revisited, indicating that retrospective memory plays some role. However, their task presented only two possible saccade targets at a time, and previously inspected items were often absent from the screen for several saccades before reappearing as possible saccade targets. Because inspected items were not constantly visible, their results might have underestimated retrospective memory. To get around this possible confound, we used a series of tasks in which all search items were visible throughout a trial. By moving inspected items (move-old) or uninspected items (move-new) to new locations during saccades, we were able to selectively remove the potential contributions of retrospective and prospective memory to the search process, respectively. Performance in these conditions was compared to a static condition in which items did not move. For both movement conditions, performance was poorer compared to the static condition. A comparison between the static and move-new condition suggests that subjects were able to plan at least 10 moves in advance, indicating a strong prospective component. Likewise, subjects were less likely to revisit inspected items in the static condition compared to the move-old condition, suggesting that they can keep track of at least the last 7 items.
National Institute of Health grant R01 MH64505