How fast can you change your mind? Effects of target identity cues in visual search

Abstract

How quickly can top-down information about a target influence visual search? To find out, we varied the SOA between the appearance of a 100% valid cue and a conjunction search stimulus. There were 24 different possible pairings of target and distractors. “Picture” cues were exact copies of the target. “Word” cues were descriptions (“red horizontal”). Cue-stimulus SOA varied from 0 to 800 msec. A new target was picked pseudo-randomly on each trial with constraints that permitted runs of the same target for 2 or 3 trials. Two control conditions were run: No Cue (find the odd item) and No Variation (same target for100 blocked trials). The No Cue condition is a ceiling condition, producing RTs that average about 1300 msec. The No Variation condition is a baseline producing RTs that average about 600 msec. The top-down information of the cue moves the RT from the ceiling toward the baseline. A picture cue preceding the stimulus by 200 msec is adequate to bring RT down to the No Variation baseline. Even a 50 msec SOA picture cue had a substantial effect. Word cues were less effective. Unsurprisingly, they took longer to become fully effective. Even after an 800 msec SOA, the RT remained 200 msec above the No Variation baseline. However, if the same cue was repeated twice in a row, picture cue RTs were unchanged but word cue RTs became about 100 msec faster. With word cues, the stimuli on trial N acted as a prime for trial N+1. Seeing the target on trial N was not critical. The same priming benefit occurred on trial N+1 when trial N was a target absent trial as when it was a target present trial. Picture cues seem to provide their own prime. We conclude that one difference between picture and word cues may be the ability of picture cues to produce priming that word cues cannot produce.