Barrett, D.
School of Psychology, College of Medicine and Biological Sciences, University of Leicester, Leicester, UK.
Recent neuroimaging evidence suggests visual short term memory (VSTM) is subserved by separate spatial and non-spatial components. This study uses a change detection task to investigate whether and how these components combine. Observers were presented with memory and probe arrays separated by an ISI of 1500 ms. Memory arrays contained three or four uniquely oriented Gabor patches. Probe arrays contained two Gabor patches randomly selected from the memory array; one identical and one that had changed (target). Targets could change their orientation, location or a combination of both and change in each dimension was manipulated using five equally spaced step sizes. Observers reported the identity of the target on each trial and the probability of a correct response was compared across conditions. The results revealed a linear relationship between step size and target detection in all three conditions. Detection thresholds (P =.75) for orientation targets were smaller than those for location targets. Detection thresholds for combined and orientation targets were equivalent. These findings support independent spatial and non-spatial components in VSTM. When target-change occurs across both components, performance appears to be based upon a winner-takes-all competition between spatial and non-spatial information.