Abstract. This research addressed current controversies concerning the contribution of semantic conflict to the Stroop interference effect and its reduction by a single-letter coloring and cueing procedure. On the first issue, it provides, for the first time, unambiguous evidence for a contribution of semantic conflict to the (overall) Stroop interference effect. The reported data remained inconclusive on the second issue, despite being collected in a considerable sample and analyzed with both classical (frequentist) and Bayesian inferential approaches. Given that in all past Stroop studies, semantic conflict was possibly confounded with either response conflict (e.g., when semantic-associative items [ SKYblue] are used to induce semantic conflict) or with facilitation (when color-congruent items [ BLUEblue] are used as baseline to derive a magnitude for semantic conflict), its genuine contribution to the Stroop interference effect is the most critical result reported in the present study. Indeed, it leaves no doubt – in complete contrast to dominant single-stage response competition models (e.g., Roelofs, 2003 ) – that selection occurs at the semantic level in the Stroop task. The immediate implications for the composite (as opposed to unitary) nature of the Stroop interference effect and other still unresolved issues in the Stroop literature are outlined further.

Previous studies (Augustinova et al., 2018;Li & Bosman, 1996) have shown that the larger Stroop effects reported in older adults is specifically due to age-related differences in the magnitude of response, and not semantic, conflict, both of which are thought to contribute to overall Stroop interference. However, the most recent contribution to the issue of the unitary vs. composite nature of the Stroop effect (Parris et al., 2021) argues that semantic conflict has not been clearly dissociated from response conflict in these or any other past Stroop studies, meaning that the very existence of semantic conflict is at present uncertain. To distinguish clearly between the two types of conflict, the present study employed the two-to-one Stroop paradigm (De Houwer, 2003) with a color-neutral word baseline (Hasshim & Parris, 2014).This addition made it possible to isolate a contribution of semantic conflict that was independent of both response conflict and Stroop facilitation. Therefore, this study provides the first unambiguous empirical demonstration of the composite nature of Stroop interference -as originally claimed by multi-stage models of Stroop interference (Zhang & Kornblum, 1998; Zhang et al., 1999). This permitted the further observation of significantly higher levels of semantic conflict in older adults, whereas the level of response conflict in the present study remained unaffected by healthy aging -a finding that directly contrasts with previous studies employing alternative measures of response and semantic conflict. Two qualitatively different explanations of this apparent divergence across studies are discussed.

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This study provides evidence of the clinical utility of self-imagining as a mnemonic strategy in schizophrenia patients.