Rapid approach-avoidance responses to emotional displays reflect value-based decisions: Neural evidence from an EEG study.

The ability to swiftly and accurately respond to others' non-verbal signals, such as their emotional expressions, constitutes one of the building blocks for social adaptation. It is debated whether rapid action tendencies to socio-emotional signals solely depend upon stimulus-evoked pre-decisional motor bias or can also engage goal-directed (decisional) processes that involve the arbitration between action alternatives. Here, we used drift diffusion models (DDMs) of choice and electroencephalography (EEG) to investigate the impact of threat-signaling individuals (angry or fearful) on spontaneous approach-avoidance decisions. Participants choose to avoid angry individuals more often than fearful ones and this effect was stronger for intense expressions. Diffusion models showed that this pattern of choice was accounted for by a process of value-based evidence accumulation, suggesting an active competition between action options. At the brain level, we found that EEG activity preceding movement initiation (200 ms) in a mid-frontal cluster of electrodes - sourced in the orbital and ventromedial frontal cortices - encoded value difference between chosen and unchosen options, thus predicting participant's choices on a trial-by-trial basis. Furthermore, value difference also modulated EEG signal during feedback about the decision. Altogether, the present findings convincingly support the underestimated influence of implicit goal-directed mechanisms in approach-avoidance responses to socio-emotional signals.