NEITHER A RESPONSE NOR STIMULUS SET-SIZE EFFECT FOUND IN THE MANUAL STROOP TASK

Existing computational models of the Stroop task differ in predictions concerning the set-size effect, which is the relation between a number of stimuli/responses and the magnitude of the Stroop interference. However, relevant empirical data is not unequivocal, as some studies reported no set-size effects, while others found substantial set-size effects. We administered two experiments in order to resolve this discrepancy in the case of the manual Stroop task. Experiment 1 compared conditions including four, six, and eight stimulus/response mappings in the picture-word task. No reliable set-size effects were found, apart from a weak effect observed when a working memory load imposed by the task was deliberately decreased. Experiment 2 tested conditions consisting of four versus eight mappings in the colour-word task, and it replicated results of Experiment 1. As both experiments had sufficient power to detect set-size effects if they existed, our data are inconsistent with models predicting such effects.