Phasic alertness generates urgency and amplifies competition between evidence accumulators

Abstract 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.