Working memory load and the Stroop interference effect

Although the effect of working memory (WM) load on the degree of distractor processing has been investigated in a number of paradigms, a common feature in prior research is that the target and distractors pertain to different objects. The present experiments examine the effect of WM load on distractor interference when the relevant and irrelevant features belong to the same object. In Experiment 1, participants saw stimulus displays that consisted of a memory set followed by a Stroop stimulus, whose colour and meaning were either unrelated or incongruent. The task was to make a speeded response to the colour of the target while holding either one or six digits in memory. Although a significant Stroop interference effect was found, its magnitude was not influenced by WM load. Experiment 2 manipulated the size of attentional focus in addition to WM load and the response congruency between the relevant and irrelevant features of Stroop stimuli. Again, there was a strong Stroop interference effect, but no effect of WM load or attentional focus. These results suggest that the effect of WM load on selective attention may be more complex than was previously conceived. They also emphasize the importance of stimulus structure in understanding the effect of WM load on selective attention.