Does unconscious control depend on conflict?

Unravelling the mechanisms that trigger cognitive control is a central question in cognitive science. Cognitive conflict is closely associated with the activation of cognitive control, helping individuals to follow their own goals. In this study, we examined whether the association of conflict and control holds when people are not aware of their intentions (i.e., they experience involuntariness regarding their behaviours). To induce unconscious control, we employed a posthypnotic suggestion (word blindness: that words will appear as a meaningless foreign script) on highly suggestible participants, a manipulation which has previously been shown to halve the Stroop interference effect. To alter the amount of conflict, we manipulated the proportion of incongruent, congruent and neutral Stroop trials between blocks in two experiments. The analyses revealed that the Stroop effect was reduced by the suggestion in the high conflict conditions (conditions with 33% or more incongruent trials), and barely at all in the low conflict conditions (conditions with 10% incongruent trials) compared to no suggestion conditions, thus, supporting the idea that a certain amount of conflict is required to activate unconscious control. This finding can also be interpreted in light of the two competing accounts of the word blindness effect (de-automatisation of reading and response competition models). The results imply that conflict between the response options occurs even in the suggestion condition and so the word blindness suggestion does not influence semantic processing as the de-automatisation of reading account postulates, rather, it is more likely that the suggestion facilitates the reduction of response competition.