By combining the semantic Stroop paradigm (e.g., Klein in American Journal of Psychology 77:576–588, 1964) with a single-letter coloring (SLC) procedure (e.g., Besner et al. in Psychonomic Bulletin & Review 4:221–225, 1997), this research investigated whether the frequently reported Stroop-related event-related potential (ERP) effect arising about 400 ms after stimulus onset (Ninc) is sensitive to the semantic and/or the response conflict. Consistent with our past findings (e.g., Augustinova et al. in Psychonomic Bulletin & Review 17:827-833, 2010), SLC speeded up reaction times for standard-incongruent items only, indicating that SLC reduced the response conflict that these (but not color-associated and neutral) items involve. Ninc amplitudes were more negative for standard-incongruent and color-associated than for color-neutral items. Importantly, this difference was not modulated by SLC. Hence, the behavioral and ERP results conjointly suggest that the Stroop-related Ninc is sensitive to semantic rather than to response and/or general conflict.
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In order to designate the relative negativity associated with the incongruent items, as compared with the neutral ones, we opted for the label Ninc, since it is agnostic with regard to the exact timing (300–500 ms), topography, and functional characteristics of this Stroop-related effect.
Because color associates (SKY green) are displayed in a color that is different from the one they are associated with (i.e., sky with blue), this color—which is retrieved when the word dimension is read—subsequently conflicts with the meaning of the word’s color dimension (i.e., green for SKY green). But since color associates do not activate incorrect motor responses (e.g., say “blue”/press blue for SKY green ; e.g., Schmidt & Cheesman, 2005), their processing involves no response conflict.
The same analysis on error rates only revealed the effect of stimulus type, F(2, 54) = 12.48, p < .001, η p 2 = .32 (see Table 1).
Indeed, the direct analysis of magnitudes for both standard and semantic Stroop interference (observed at each level of coloring; see Table 1) revealed the expected orthogonal interaction, F(1, 27) = 9.07, p < .01, η p 2 = .25. Accordingly, its decomposition showed that the standard Stroop interference of 75 ms in ALC was reduced to 25 ms in SLC, F(1, 27) = 8.97, p < .01, η p 2 = .25, whereas semantic Stroop interference remained statistically equivalent in both the ALC and SLC conditions (17 and 10 ms, respectively), F(1, 27) = 0.38, p = .54, n.s.
It should be recalled that Ninc is a relative negativity resulting from the difference between incongruent and color-neutral items.
M SLC = –1.08, SE SLC = 0.39 versus M ACL = –0,77, SE ALC = 0.34.
The same reasoning actually applies to the use of standard-congruent items (BLUE blue) as a baseline, because such items elicit facilitation (i.e., qualitatively different phenomenon from interference that incongruent items involve; see, e.g., Brown, 2011), due, respectively, to semantic and response compatibility.
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All the authors wish to thank Pierre Chausse for technical support and Derek Besner, Martin Heil, and one anonymous reviewer for their helpful advice, comments, and suggestions on previous drafts of the manuscript.
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Augustinova, M., Silvert, L., Ferrand, L. et al. Behavioral and electrophysiological investigation of semantic and response conflict in the Stroop task. Psychon Bull Rev 22, 543–549 (2015). https://doi.org/10.3758/s13423-014-0697-z
- Semantic conflict
- Single-letter coloring
- Stroop interference
- Response conflict