Distractor interference stays constant despite variation in working memory load

Previous studies show that working memory (WM) plays an important role in selective attention, such that high WM load leads to inefficient distractor inhibition compared to low WM load. However, because WM load is typically manipulated via varying the number of items held in memory, when the to-be-remembered stimuli are presented simultaneously, the number of stimuli is correlated positively with the extent of attentional focus. Because attentional focus is known to influence the efficiency of distractor inhibition, the systematic pairing between WM load and attentional focus makes it unclear whether the differential distractor interference in the low vs. the high WM load conditions is primarily caused by a difference in WM load or a difference in the extent of attentional focus. In four experiments we examine the effect of WM load on distractor processing while holding constant the extent of attentional focus. Our results show that WM load affected distractor processing only when it was positively correlated with the extent of attentional focus. When the latter was held constant, the effect of WM load became negligible. Furthermore, when low WM load was paired with a wide attentional focus and high WM load was matched with a narrow attentional focus, greater distractor processing was found when the WM load was low rather than when it was high. These results suggest that efficient distractor inhibition may require only minimal working memory resources, and that the effect of working memory on distractor processing is more complex than was previously assumed.