Objects or Locations in Vision for Action? Evidence from the MILO task.

In the multi-item localization task (MILO, Thornton & Horowitz, 2004), observers are asked to find an ordered sequence of targets. We can measure the influence of both past actions and future plans on search for the current target. Our previous work with static search arrays found evidence for both retrospective and prospective memory. Responding to a target eliminated its influence on subsequent responses, while observers consistently planned ahead at least one item into the future. Here we asked whether these effects were based in location- or object-based reference frames. We used dynamic arrays in which observers had to search for multiple moving targets. Our results suggest that observers can still plan ahead effectively in this dynamic environment, indicating that future target objects can be tracked as they change position. However, memory for previous targets is essentially eliminated, suggesting that locations, not objects, were being tagged in our previous work.