Psychonomic Bulletin & Review

The visual system utilizes a variety of attentional mech-anisms to prioritize the selection of relevant information in the environment. Recently, Watson and Humphreys (1997) showed that visual search can be significantly im-proved when the presentation of search objects is sepa-rated in time. If a subset of distractors is previewed for at least 400 msec before the search display, the previewed objects can be excluded from search. This phenomenon, termed the preview effect, appears to be fairly robust across a variety of conditions; it occurs with previewed subsets of up to 15 objects (Theeuwes, Kramer, & Atchley, 1998) and is not affected if search objects change colo