Search for multiple targets: evidence for memory-based control of attention

There are two opposing models with regard to the function of memory in visual search: a memory-driven model and a memory-free model. Recently, Horowitz and Wolfe (2001) investigated a multiple-target search task. Participants were required to decide whether or not there were at least n targets present. They demonstrated that the reaction time x n function has a positive and accelerated curve. They argued that the memory-free model predicts this curve, whereas the memory-driven model predicts a linear function. In this study, I varied the total set sizes of a multiple-target search task and fitted the models separately for each n condition. The model fit indicated that the memory-driven model is more appropriate than the memory-free model in each n condition. These results suggest that an amnesic process does not cause the positive accelerated curve of the reaction time x n function but that it is the result of the time needed to examine each additional n item.