Irrelevant Task Difficulty Modulates the Emergence of Task Conflict

In cognitive control tasks, participants are typically instructed to respond to a task-relevant dimension of a stimulus while ignoring the task-irrelevant one(s). In such experiments, task conflict reflects the additional effort associated with performing two tasks, such as identifying the color while reading the word in the color-word Stroop task. Task conflict is commonly inferred by comparing conditions that consist of two tasks (e.g., congruent and incongruent trials) with conditions that only consist of one task (meaningless non-word neutral trials). In three experiments, we used a color-digit Stroop task that varied in the difficulty of the irrelevant dimension of the stimuli, with these differences explicitly examined in a separate control experiment. While information conflict was evident across all experiments, we found differences in task conflict, so the harder it was to perceive the task-irrelevant dimension, the stronger the task conflict became. These findings demonstrate for the first time that task conflict emerges on a continuum, scaling with the level of engagement or processing demands associated with the irrelevant task. Moreover, these results suggest that our ability to inhibit the involuntary activation of an unwanted process is restricted. Therefore, despite the resource-intensive demands of completing the irrelevant task, it still takes place.