Urgency Signal

The urgency signal is a global, non-selective modulation of response threshold in evidence-accumulation models of action selection. Proposed by C. Tommi Muller, Leendert van Maanen, and others, it explains how decision-makers can speed up their responses under time pressure without fundamentally altering the evidence-evaluation process itself.

In the gated accumulation model and related race models, each action candidate accumulates evidence until it crosses a threshold, at which point it is executed. The urgency signal lowers this threshold globally across all candidates, making it easier for any of them to trigger. The result is faster responses at the cost of lower accuracy — the classic speed-accuracy tradeoff.

The urgency signal is distinct from changes in the input evidence or in the drift rate of accumulation. It is a control parameter that reflects the observer's internal estimate of how much time remains or how costly delay is. Neurophysiological evidence suggests the urgency signal is implemented in the basal ganglia and associated cortical circuits, possibly through dopaminergic and noradrenergic modulation of striatal and prefrontal activity.

The concept is important because it separates the quality of a decision from the commitment to act. An agent can believe one option is superior while still being willing to execute an inferior one if the cost of waiting exceeds the expected benefit of additional evidence. The urgency signal is the mechanism that implements this tradeoff.