Stroop can occur without Garner interference: strategic and mandatory influences in multidimensional stimuli

Stroop and Garner interference were studied in two experiments involving stimuli with several irrelevant features. Using these stimuli, which were more complex than those usually used in perceptual interference studies, a new phenomenon occurred: Stroop effects without a corresponding Garner interference were obtained in four out of six nontarget conditions, two with local and two with global targets. The effects with local targets were anomalous: on one dimension, incongruous Stroop stimuli were better than congruous ones, while on the other dimension, effects were restricted to a condition in which all nontargets were congruous. With global targets, more consistent cases of Stroop-without-Garner effects were obtained. All Stroop effects were replicated in Experiment 2, in which presentation time was varied. The effects showed a strong dependency on presentation time, in such a way as to suggest a dynamic growth of the percept. The results were interpreted in terms of an interaction between automatic and strategic components of perceptual processes, in agreement with a recently introduced perceptual-organization model, which yields a new interpretation of priming and interference phenomena.