Abstract
In an inefficient visual search task, when a set of distractors (old items) is presented before a set of target and distractors (new items), the search becomes efficient and independent of the set size of old items (visual marking: Watson & Humphreys, 1997). This effect is said to occur because the locations of the old items are inhibited before the new items appear. This study used a probe-detection task to examine whether the inhibition occurs only at the locations of the old items or at and around the locations of old items. In Experiment 1, participants performed a preview search task in which they searched for a target among the old and new items in 2/3 of the trials. In these trials, the old items were presented for 1s before the new items were added. In the remaining trials (signaled by a tone), the displays were identical to the preview search trials, except that the participants had to detect a probe dot that appeared in the display after the new items appeared and the reaction time to detect the probe was measured. The result revealed that the reaction times at locations around the old items were longer than for the blank region where no items were presented, and as long as that at the location occupied by old items. In Experiment 2, we tested whether the inhibition around the old items was induced before or after the new items appeared because the inhibition of visual marking occurs beforehand. The result indicated that probe detection around the old location took longer than in the blank region before new items appeared. These results suggest that the inhibition of visual marking occurs not only at the location of old items, but also propagates around the location of the old items.