Phasic Alertness Impairs Cognitive Control by Amplifying Competition between Evidence Accumulators

Although phasic alertness generally benefits cognitive performance, it often increases the impact of distracting information, resulting in impaired decision-making and cognitive control. However, it is unclear why phasic alertness has these negative effects. Here, we present a novel, biologically informed account, according to which phasic alertness generates a transient, evidence-independent input (TEI) to the decision process. This shortens overall response times but also amplifies competition between evidence accumulators, thus slowing down decision-making and impairing cognitive control. The key hypotheses of this account are supported with pupil measurements and electrophysiological data from human decision-makers of either sex performing an arrow flanker task. We also show that a computational model of the flanker task that incorporates a TEI can reproduce the behavioral effects of phasic alertness but only when the evidence accumulators compete with each other through lateral inhibition. Our results reveal a close interplay between dynamic changes in alertness, cognitive control, and evidence accumulation.