Psychonomic Bulletin & Review 1999. 6 (3). 449-455 Unconsciously controlled processing: The Stroop effect reconsidered DEREKBESNERand JENNIFER A. STOLZ University ojWaterloo, Waterloo, Ontario, Canada The Stroop effect is widely consideredto be compelling evidence that an acquired skill such as read­ ing is "automatic" in the sense that lexical/semantic analyses of single words cannot be prevented, even when they are irrelevant and harmful to the task at hand. This view is challenged by a series of three experiments in which the presence/absence of a Stroop effect depends on (1) whether all ofthe target elements are colored or not, in conjunction with (2) whether the target and the spatially distinct color word distractor belong to the same domain or not. A framework is offered in which domain-specific encoding algorithms play a major role. Skilled word recognition is typically unconscious, but is char­ acterized better as contextually controlled, rather than "automatic." It is well established that, for skilled readers who are Stolz, 1999, for related findings). Iflexical/semantic pro­ explicitly told to refrain from reading a word, it takes cessing associated with word recognition is not control­ more time to identify the word's color ifthe word and its lable, as much ofa Stroop effect should have been found color are incongruent (e.g., red letters spelling the word in the single-colored-letter condition as in the all-letters­ green) than it does to identify the color ofthe word ifthe colored condition. Given that there is little or no Stroop word and its color are congruent (e.g., green letters effect in the former condition, characterizing word recog­ spelling the word green). Many variants ofthis phenom­ nition as automatic in the sense defined above does not enon have been explored empirically, theoretically, and provide an adequate account. computationally by cognitive scientists in more than 500 The purpose of the present paper is twofold. First, it papers since the publication of Stroop's (1935) seminal demonstrates that a Stroop effect is present when the color work (see MacLeod's, 1991, review). A core assumption carrier stimulus and the color word are spatially separated. ofmost ofthe theoretical accounts is that skilled readers Variations on this theme have ofcourse been reported be­ process the irrelevant word without consciousness or in­ fore (e.g., by Brown, Roos-Gilbert, & Carr, 1995). What tent. Reading the word is said to be automatic in the sense is new is that this variant ofthe Stroop effect can be largely that readers cannot refrain from computing the meaning of eliminated through a manipulation of the target's color the word despite explicit instructions that they should not, extent (whole/part) despite the fact that all the letters in and despite the fact that such computation impairs color the irrelevant and spatially distinct color word always ap­ identification performance.' The Stroop effect is thus pear in white (a color that is not in the response set). The seen as the "gold standard" ofautomatized performance second purpose ofthe paper is theoretical; we argue that (MacLeod, 1992). This view has been expressed in a va­ the results of the experiments distinguish between sev­ riety of sources, including journal articles, specialized eral competing accounts ofhow the reduction/elimination books on reading, and introductory and cognitive psy­ ofthe Stroop effect in this preparation comes about. chology textbooks. There is, however, a problem with the widespread Levels ofProcessing view that the word recognition processes that produce Stolz and Besner (1996, 1998; see also Bauer & Besner, "the" Stroop effect are not open to control.? Although a 1997; Besner & Stolz, 1999; Besner et al., 1997; Chiappe, Stroop effect is observed when the entire word is colored Smith, & Besner, 1996) have suggested that instead of (the standard condition), it can be eliminated when only word recognition being characterized as "automatic," the a single letter in the word is colored (Besner, Stolz, & mental set adopted by subjects exerts a powerful influence Boutilier, 1997; see also Bauer & Besner, 1997; Besner & on performance. The default set is to process words to the semantic level, a useful set outside the laboratory where important information is often conveyed by print This work was supported by Grants A0998, OGP018390, and (e.g., STOP, BAR, RESTAURANT, BANK, and BATHROOM). EQPOI87220 from the Natural Sciences and Engineering Research Nonetheless, this default mental set can be overridden by Council of Canada. Some of these data were presented at CSAIL (1996) the context in such a way that semantic activation is cur­ and at the annual meeting ofthe Psychonomic Society (1997). Corre­ spondence should be addressed to D. Besner, Psychology Department, tailed. For example, the well-documented "semantic University of Waterloo, ON N2L 3Gl, Canada (e-mail: dbesner@ priming" effect in lexical decision can be eliminated watarts.uwaterloo.ca). when subjects search the prime display for a letter target 449 Copyright 1999 Psychonomic Society, Inc. 450 BESNER AND STOLZ (see, e.g., Chiappe et al., 1996; Friedrich, Strayer, & Neely, 1991, for reviews). This view therefore predicts Christensen, 1997; Smith, Theodor, & Franklin, 1983; that the two conditions should produce the same-sized Stolz & Besner, 1996, 1998). Coloring only a single let­ Stroop effect. In contrast, the levels hypothesis advanced ter instead ofall letters in a Stroop task may also serve to by Besner et al. (1997) to account for the data from the override the default mental set, the consequence being a paradigm where word and color are integral predicts that reduction or elimination ofsemantic activation and thus the single-colored-letter condition in the present para­ the reduction or elimination ofthe Stroop effect. digm should produce little or no Stroop effect in compar­ This description is not incompatible with the account of­ ison with the all-colored-letters condition, provided that fered by Kahneman and Henik (1981). In their view, col­ one additional assumption is made-namely, that sub­ oring only a single letter in a word renders a letter (rather jects find it difficult to maintain two different mental sets than the word) the perceptual object, thus making it less simultaneously. One ofthese sets is the normally opera­ susceptible to a Stroop effect, which arises through higher tive default set that processes words in such a way that level processing.' Yet another way ofdescribing Kahne­ semantics are activated. This set will dominate when the man and Henik's account is to suppose that coloring a sin­ target stimulus is a word in which all the letters are col­ gle letter changes the distribution ofspatial attention from ored, and it is therefore applied to reading both the target the default value of broad beam (distributed across the stimulus and the irrelevant color word. The other set is word) to narrow beam (focused on the space occupied by the one needed to process the single colored letter in the a letter). The effect ofchanges in the distribution ofspa­ target (where semantic activation does not occur, or occurs tial attention has largely been ignored in both the visual in very reduced form), and it is also applied to the pro­ word recognition and Stroop literatures, but a number of cessing ofthe irrelevant color word. reports strongly suggest that spatial attention plays a crit­ A version ofthis assumption has been examined before ical role (e.g., Besner & Stolz, 1999; Johnston & Me­ in the context ofthe so-called global/local processing lit­ Clelland, 1974; LaBerge, 1983; McCann, Folk, & John­ erature, although it is not referred to as "set" there, but ston, 1992; Stolz & McCann, 1999). In particular, ifspatial rather as the ability to focus "attention," and it is not clear attention needs to be distributed across the word as a pre­ whether semantics is involved or not. In the context of liminary to visual word recognition, then narrowing the processing pairs oflocal/globalletters (large letters com­ beam ofspatial attention so that it is focused on an indi­ posed ofsmall letters), where one object is attended (the vidual letter should make word recognition problematic. target) and the other not, Paquet and Merikle (1988) re­ In that vein, Johnston (1981) reported that the word supe­ port that interference from the unattended object depends riority effect in Reicher's (1969) perceptual identification on the level ofprocessing of the attended object. When task is eliminated ifsubjects are told to attend to a spatial the attended object required local level processing, there position that will be occupied by a particular letter when was little interference from the global level of the unat­ the word display is subsequently presented. Relatedly, tended object, but there was a large amount ofinterference Besner and Stolz (1999) reported that the Stroop effect can from the locallevei. Similarly, when the attended object be reduced in magnitude or eliminated when a single let­ required global level processing, there was more interfer­ ter position in a colored word is precued as compared to ence from the global level ofthe unattended object than when all the letter positions are precued. from the locallevei. Although not interpreted in quite this Is it possible to discriminate between any ofthese ac­ way, Paquet and Merikle's findings are consistent with counts, or are they just different verbal descriptions that the idea that it is difficult to hold two different mental reduce to the same operation in this context? Imagine a sets simultaneously. When two objects are in the visual paradigm in which two words appear on the screen. One, field, one relevant and the other not, processing can be the color carrier, appears at fixation and consists of a done at the local level on both, or at the global level on neutral word (i.e., one that is not color related).