Strategy or local control? Interaction of Gratton effect and proportion’s effect in the Stroop test

Abstract

Models of cognitive control contain the mechanism of the general strategy of solving a task and control of specific stimuli special mechanisms. There is an ongoing discussion as to which control is responsible for the Gratton effect and the Stroop test’s proportion effect. The Gratton effect consists in decreasing the Stroop effect after an incongruent stimulus, the proportion effect is to increase interference when incongruent stimuli predominate among other types of stimuli. In this study, we set out to test whether there would be an interaction between these effects. If it is detected, we can say that both effects of study are produced by a general cognitive mechanism. Similar studies of general strategy using the Stroop task include congruent and incongruent stimuli. Congruent stimuli produce a response facilitation effect that is mixed with an interference effect, making final interpretation difficult. To avoid this, we used different proportions of incongruent and neutral stimuli. We conducted three experiments using different proportions of incongruent versus neutral stimuli (66:33/33:66 and 80:20/20:80), as well as the type of design (intragroup and intergroup plans). Only the Gratton effect was detected in the experiments performed — no proportion effect or significant interaction between the Gratton and proportion effects was found. In three experiments (N = 70), only indirect evidence was found for the effect of proportion on the Gratton effect. These results are difficult to explain in terms of “strategic” interference model who explain both effects by a change in the global strategy for solving the task. Given the systematic lack of interaction between the Gratton effect and other effects in the literature, we can say that the Gratton effect is caused by a local control system, which the proportion effect influences, if at all, only slightly. The connection between the proportion effect and strategic control and the factors that mediate it are discussed.