Academic journal article Psychonomic Bulletin & Review

The Context-Specific Proportion Congruent Stroop Effect: Location as a Contextual Cue

Academic journal article Psychonomic Bulletin & Review

The Context-Specific Proportion Congruent Stroop Effect: Location as a Contextual Cue

Article excerpt

The Stroop effect has been shown to depend on the relative proportion of congruent and incongruent trials. This effect is commonly attributed to experiment-wide word-reading strategies that change as a function of proportion congruent. Recently, Jacoby, Lindsay, and Hessels (2003) reported an itemspecific proportion congruent effect that cannot be due to these strategies and instead may reflect rapid, stimulus driven control over word-reading processes. However, an item-specific proportion congruent effect may also reflect learned associations between color word identities and responses. In two experiments, we demonstrate a context-specific proportion congruent effect that cannot be explained by such word-response associations. Our results suggest that processes other than learning of word-response associations can produce contextual control over Stroop interference.

The Stroop task (Stroop, 1935) requires participants to identify the ink colors of color words (for a review, see MacLeod, 1991). Responses are typically slower on incongruent trials (RED in blue ink) than on congruent trials (BLUE in blue ink). The difference in response latency between congruent and incongruent trials is often taken as a measure of the contribution of automatic word-reading processes to performance (Lindsay & Jacoby, 1994). When the Stroop item is congruent, the word-reading process facilitates compatible ink color responses. In contrast, for incongruent items, the word-reading process conflicts with the ink color response and slows performance.

A strong automaticity hypothesis would predict that Stroop effects are entirely insensitive to context. However, several researchers have demonstrated that the proportion of congruent items in a Stroop task can modulate the size of Stroop interference (e.g., Logan & Zbrodoff, 1979; Lowe & Mitterer, 1982; West & Baylis, 1998), with high proportions of congruent items producing large Stroop effects. The effect of proportion congruent on the size of the Stroop effect is commonly attributed to changes in experiment-wide word-reading strategies that depend on the likelihood of congruency. For example, participants in a high-proportion congruent context may adopt the strategy of allowing word reading to influence the selection of responses. A consequence of this strategy would be relatively large Stroop effects, because word reading makes performance faster on congruent trials, but slower on incongruent trials. In contrast, participants in a low-proportion congruent context may adopt the strategy of preventing word reading. This strategy would slow responses on congruent trials, but reduce conflict on incongruent trials, thereby yielding a smaller Stroop effect.

The idea that proportion congruent effects on Stroop interference necessarily reflect changes in experimentwide word-reading strategies was challenged recently by Jacoby, Lindsay, and Hessels (2003). In their study, the proportion of congruent items was manipulated between different sets of Stroop items. High-proportion congruent items were created from WHITE, RED, and YELLOW word/color combinations, and low-proportion congruent items were created from BLACK, BLUE, and GREEN word/ color combinations. These mostly congruent and mostly incongruent item types were mixed at random across the experimental session, so that participants could not predict whether the upcoming trial was likely to be congruent or incongruent. Consequently, any experiment-wide word-reading strategy employed by participants could be regarded as identical for the two item types. Nevertheless, the high-proportion congruent items produced a larger Stroop effect than did the low-proportion congruent items. Jacoby et al. labeled this difference an item-specific proportion congruent (ISPC) effect.

Because the ISPC effect cannot be explained via experiment-wide strategies implemented by a central task-demand mechanism (Cohen, Dunbar, & McClelland, 1990), Jacoby et al. …

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