Abstract
In visual search tasks, if a subset of the search items (without the target) is presented at least 400 ms before the full set is in view, visual search efficiency is improved as if only the second set of items had been searched. This phenomenon is known as visual marking, and is thought to involve inhibitory-tagging of old items. This study investigates whether this inhibitory-tagging is location-based or feature-based. Subjects searched for a sideway T among Ls of identical color and regular Ts and upside-down Ts of a second color, and report the orientation of the target T. In addition, to eliminate the contribution of bottom-up attentional capture by the onset of the second set of items, we included a 200ms blank display between the initial preview and the final search display. In Experiment 1, we tested four conditions: feature search (T amongst Ls), conjunction search (T amongst full set of distractors) and two preview conditions. In the same-location preview condition, the previewed items remained at the same location when the full search display was presented, whereas in the different-location preview condition, the previewed items appeared at previously unoccupied locations. Our results showed an identical degree of marking in the same- and different-location preview conditions, indicating that knowing the color of the previewing items was sufficient information for “marking” which items not-to-search in the full display. In Experiment 2, we further tested this feature-based marking by replacing the preview display with a color “blob”, which indicated the color of the subset of items in the final display NOT to search. Search efficiency was identical in the blob condition compared to the same-location preview condition, even though there was a significant main effect, with RTs in the blob condition being significantly slower. Implications regarding theories of visual marking will be discussed.
This work was supported by a University of Illinois graduate fellowship to H. C.