Two types of conflict underlie performance in the Stroop task—informational (between the incongruent word and its ink color) and task (between the relevant color-naming task and the irrelevant word-reading task). We manipulated congruent-to-neutral trial ratio in an attempt to reveal whether task conflict can be monitored and controlled in the absence of an informational conflict. In our first experiment, no incongruent trials were included, thus allowing examination of a pure task conflict situation. The results revealed an impressively large facilitation when most of the stimuli were congruent and a smaller yet significant facilitation when most of the stimuli were neutrals. In Experiments 2, exposing participants to incongruent trials during pre-experimental practice (but not during the experimental blocks) slowed down the responses to congruent trials, resulting in a reduced facilitation effect in the mostly congruent condition, and in a negative facilitation in the mostly neutral condition. In our third experiment, we replicated our results, eliminating possible contingency and frequency biases. Overall, our findings show that experiencing, or at least expecting, informational conflict is essential to reveal conflict, while control is recruited through task demands. This challenges previous findings and points out that additional research is needed to clarify the necessity of informational conflict for conflict detection.
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We use the term “task conflict” to describe a situation in which participants perform an irrelevant task even though they are not supposed to do so. We use this particular term because it was originally suggested by Macleod and Macdonald (2000), and not because we think it is the most suitable.
In this study, we focus on the difference between task conflict and informational conflict (MacLeod & Macdonald, 2000). Informational conflict refers to the difference in information provided by the color of the word and its meaning in the case of incongruent trials. However, incongruent trials as used in our experiment also include two additional sources of conflict, that is, a response conflict and a semantic conflict. Specifically, in incongruent stimuli, there is a semantic conflict because two distinct mental representations are activated at the level of semantic or conceptual encoding (e.g., Brown & Besner, 2001; Treisman & Fearnley, 1969; Zhang & Kornblum, 1998) or conceptual (lemma) selection (Roelofs, 2003), but there is also response conflict because each of them leads to a different response. Thus in the standard design of the Stroop task as used in the present study, informational conflict is confounded with semantic and response conflicts. In the present study, we do not distinguish between these types of conflict and our use of the terms "informational conflict" covers all of them.
It was suggested by one of our reviewers that (response) conflict is not entirely absent but it is lower for congruent trials than for neutral trials, because the correct response is more strongly activated (and the incorrect response is less strongly activated) in congruent stimuli, which implies a smaller Hopfield energy in the response layer (Botvinick et al., 2001). In addition, Botvinick, Nystrom, Fissell, Carter and Cohen (1999, see also Yeung, Cohen, & Botvinick, 2011) stated that congruent trials may involve other types of conflict, such as conflict between task representations (i.e., task conflict), trial-to trial fluctuations in attentional focus, misperceiving the stimulus, preparing the wrong response, etc.
We carried out replications of Experiments 1 and 2 in which we matched the number of practice trials (60 trials—56 neutral/congruent trials and 4 congruent/neutral trials; 48 neutral/congruent trials, 6 congruent/neutral trials, and 6 incongruent trials in conditions with incongruent trials in practice). The results obtained were very similar to the ones presented in this paper.
We conducted a similar experiment using four types of neutrals while adding a small amount of incongruent trials into pre-experimental practice (as was done in Exp. 2). If changes in contingencies across conditions were sufficient to explain the pattern of results observed, once we equated the contingencies we expected to see a facilitation effect across the different task conflict conditions. On the contrary, the results obtained replicated our previous findings, showing a facilitation effect in the MC condition and a negative facilitation effect in the MN condition, thus indicating control involvement. In addition, an experiment with four types of neutrals consisting of four different shapes (e.g., *%#< in red, #%?< in blue, %*$# in green, <%#& in yellow) showed the same pattern of results.
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We thank Dr. Yulia Levin, Dr. James R. Schmidt and the two anonymous reviewers for their helpful comments. This research was supported by Grant 146/16 from the Israeli Science Foundation.
This manuscript does not contain clinical studies or patient data. All procedures performed in this study were approved by the ethics committee of the Psychology Department at Ben-Gurion University of the Negev.
Informed consent was obtained from all participants included in the study.
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Entel, O., Tzelgov, J. Focusing on task conflict in the Stroop effect. Psychological Research 82, 284–295 (2018). https://doi.org/10.1007/s00426-016-0832-8