Alertness and cognitive control: Interactions in the spatial Stroop task.

Cognitive control over information processing can be implemented by selective attention, but it is often suboptimal, as indicated by congruency effects arising from processing of irrelevant stimulus features. Research has revealed that congruency effects in some tasks are larger when subjects are more alert, and it has been suggested that this alerting-congruency interaction might be associated with spatial information processing. The author investigated the generality of the interaction by conducting a preregistered set of four experiments in which alertness was manipulated in variants of the spatial Stroop task, which involved classifying the spatial meaning of a stimulus presented at an irrelevant position. Regardless of stimulus type (arrows or words) and spatial dimension (horizontal or vertical), significant alerting-congruency interactions for response times were found in all experiments. The results are consistent with the suggestion that spatial attention and spatial information processing are important sources of the interaction, with implications for understanding how alertness is related to cognitive control.