Kinematic encoding of the speed-accuracy trade-off in approach/avoidance decisions when facing social threats.

Perceiving social threats, especially expressions of anger, increases the speed of both action selection and execution. However, it remains unclear how individuals balance speed with achieving desirable outcomes, such as threat avoidance, under these conditions. To investigate this trade-off between decision speed and accuracy, we examined the kinematics of finger-reaching movements using a "go-before-you-know" paradigm. Participants chose between two empty outer chairs in a waiting room. Two central chairs were occupied by either two individuals with neutral expressions or one neutral individual and one threatening individual. The threatening individual expressed anger or fear at one of four intensity levels. The results showed that social threats generally invigorated action decision, as high-threat trials elicited faster movements, which correlated with more direct trajectories compared to neutral trials. However, when participants chose to avoid angry individuals, the most frequent response, movements followed more central trajectories, compared to when they approached angry individuals. These findings suggest that while social threats generally invigorate action selection and execution, it is possible that the accumulation of evidence for the decision can be temporarily prolonged to enhance the likelihood of a favorable outcome, such as threat avoidance. We discuss alternative interpretations and propose the integration of these results with recent models of action decisions under perceived urgency to advance the understanding of threat-related decision-making.