Attention shifts are facilitated if the items to be attended remain the same across trials. Some researchers argue that this priming effect is perceptual, whereas others propose that priming is postperceptual, inv olv ing f acilitated response selection. The experimental f indings hav e not been consistent regarding the roles of v ariables such as task dif f iculty , response repetition, expectancies, and decision-making. Position priming, when repetition of a target position facilitates responses on a subsequent trial, is another source of disagreement among researchers. Experimental results have likewise been inconsistent as to whether position priming is dependent on the repetition of target f eatures or has an independent ef f ect on attention shifts. We attempted to isolate the perceptual components of priming by presenting brief (10–180 ms) search array s to eight healthy observ ers. The task was to identify a color-singleton letter among distractors. All stimulus presentation contingencies were randomized, and responses were unspeeded, to av oid ef f ects of observ er expectation and postperceptual
ef f ects. Repeating target color and/or position strongly improv ed
perf ormance. The ef f ects of color and position repetition were independent of one another and were stable across participants. The results argue for a strong perceptual component in priming, which biases selection toward recent target features and positions, showing that perceptual mechanisms are suf f icient to produce priming in v isual search and that such ef f ects can be elicited with limited sensory ev idence. The results are the f irst to demonstrate independent priming of color and position in the identification of brief ly presented, postmasked stimuli.