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A single novel word among several familiarized words may be localized more effectively than the familiarized words (novel popout). Early demonstrations of novel popout attributed the effect to the capture of attentional resources by novel stimuli. Klein (1995, 1996)argued that differential recollection of novel versus familiar words could alternatively account for the popout effect. In the present experiments, participants judged which of four locations contained a physically brighter word. A bright novel word was localized significantly better than a bright familiar word in one-novel/threefamiliar arrays, inconsistent with a retrievability account of novel popout. However, a bright familiar word was also localized better than a bright novel word in three-novel/one-familiar arrays, inconsistent with the mismatch theory proposed by Johnston and Hawley (1994). The results suggest that familiarity and novelty provide a perceptual segregation of the odd item; superior brightness discrimination at that location may be due either to attentional capture or to locational ambiguity within the larger group.Properties that distinguish one object from an array of others, such as luminance, color, or abrupt onset, may capture attention in a stimulus-driven fashion-that is, independent of a person's strategies or intentions (Theeuwes, 1991(Theeuwes, , 1992Yantis & Jonides, 1984; but see Jonides & Yantis, 1988). Research by Johnston and colleagues (Hawley, Johnston, & Farnham, 1994;Johnston, Hawley, & Farnham, 1993;Johnston, Hawley, Plewe, Elliott, & DeWitt, 1990) suggested that the novelty of an object may similarly capture attention, causing it to perceptually pop out against an array of familiarized items.The novel popout effect has typically been demonstrated in a task in which participants are shown an array of four different words followed by a single probe word; they then attempt to indicate the initial location of the probed word. Some of the words are familiar in the context of the experiment because they appear repeatedly across trials; other words are novel, appearing only once. If an array contains three familiar words and one novel word, localization of the novel word is likely to be enhanced relative to an all-novel array (between-arrays novel popout), and localization of a familiar word may suffer relative to an all-familiar array (familiar sink-in). In some experiments, the novel word in a one-novel array is localized better than the familiar words in that array (withinarray novel popout), despite higher performance on allfamiliar arrays than on all-novel arrays (baseline effect).This work was funded by a Faculty Research Grant awarded to the second author. We thank Molly Brown, Michelle Gruhn, Lauren May, and Tammy Schillinger for their assistance with data collection. We are also indebted to Ray Klein, Bradley Gibson, William Johnston, and Jan Theeuwes for helpful suggestions and comments on earlier versions of this manuscript. K. A. Diliberto is now at Berry College, Mount Berry, GA. Correspondence concerni...

Localization of a novel word in an array with several familiar words is typically enhanced relative to localization in an all-novelarray (between-array novel popout) and sometimes enhanced relative to familiar words in one-novel arrays (within-array novel popout), Christie and Klein (1996) have questioned the reality of the latter effect, suggesting that it may be an artifact of guessing bias, The present Experiment 1 replicated within-array novel popout with the novel word probed at chance (i.e., on only one quarter of trials). Experiments 2 and 3 demonstrated a similar popout effect for a categorically unrelated word among three categorically related words, despite superior performance on all-related arrays relative to all-unrelated arrays. Repetition of constant sets of words within the experimental context is therefore unnecessary for a popout effect, contrary to assertions by Johnston and Hawley (1994). Interitem associations appear to be sufficient to produce a popout effect; as such, "novel popout" appears to be a misnomer for a phenomenon that does not depend on novelty.The human mind often seems to favor processing of familiar or expected stimuli, as demonstrated, for example, by semantic priming (Neely, 1977), the word-superiority effect (Reicher, 1969), and frequency effects in word identification (Morton, 1969). At other times, however, novel or unexpected stimuli seem to receive preferential processing relative to familiar stimuli, as demonstrated by perceptual habituation (Sokolov, 1963), semantic satiation (Smith, 1984) and the word-inferiority effect (Healy, 1976). In visual search tasks, locating an unfamiliar target in a background of familiar distractors is easier than locating a familiar target in a background of unfamiliar distractors (Reicher, Snyder, & Richards, 1976). More generally, the mind seems to maintain two simultaneous but opposing biases: to anticipate regularities in the environment, yet to be prepared for violations of those regularities (Grossberg, 1987;Kauffman, 1995).To resolve this paradox, Johnston and Hawley (1994) proposed the mismatch theory, which has antecedents in Sokolov's (1963) dishabituation theory and Grossberg's (1987) adaptive resonance theory. According to the mismatch theory, opposing biases are instantiated at different levels ofprocessing. Higher level "identity nodes" are presumed to be activated by lower level "iconic nodes." The identity nodes are more highly activated for familiar and expected stimuli and may also activate each other through mutual excitatory connections. However, activation of identity nodes produces a top-down inhibition ofWe would like to thank Lauren May and Molly Brown for their assistance with data collection. We also thank William Johnston, Ray Klein, John Christie, and Cheryl Doland for their comments and suggestions on a previous version of this manuscript. Portions of this article were presented at the 38th annual meeting of the Psychonomic Society, Philadelphia. This work was funded by a faculty research grant awarded to 1.A...