Local spatial layout consistency affects strategies but not memory during Visual Search

Serial visual search is efficient in that participants rarely revisit previously examined items. This efficiency is partially due to the ability to remember the spatial locations of previously examined items. The current experiment examined the extent to which the consistency of local spatial layout contributes to search efficiency. Participants completed two blocks of trials. In one block, the search items were arranged in a grid layout such that the distance between any given item and its nearest neighbor was consistent. In the other block, the search items were arranged in a random layout such that the distance between an item and its nearest neighbor varied randomly. Although there was variability of the local spatial layout between the grid and random layout conditions, the global spatial layout (area/number of items) did not differ. Participants were asked to search 8, 12, or 16 icons for the presence or absence of a particular icon (e.g., Document A). For target presence trials in block 1, there was no effect of spatial layout on search RTs. However, on the target absent (TA) trials, search was significantly slower on the random layout trials than the grid layout trials. Eye movement analysis revealed that a higher number of fixations in the random layout TA trials was not due to an increase in revisits to previously examined items. This suggests that search is slower for the random layout on TA trials because participants are using a stricter stopping rule. Therefore, local spatial layout consistency affects search termination strategies but not memory during search. In addition, the relationship between random and grid layouts on TA trials reversed in block 2. This suggests that the stopping rule established in block 1carries over to block 2 even though the local spatial layout has changed.