Phasic alertness generates urgency and amplifies competition between evidence accumulators

Although phasic alertness generally benefits cognitive performance, it often increases the interference caused by 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 an evidence-independent urgency signal. This urgency signal shortens overall response times, but also amplifies competition between evidence accumulators, thus slowing down decision-making and impairing cognitive control. The key assumptions of this account are supported with pupil measurements and electrophysiological data from human decision-makers performing an arrow flanker task. We also show that a computational model of the flanker task that incorporates time-varying urgency 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 urgency, cognitive control and evidence accumulation.