Abstract
This study examined how mere co-presence and evaluative observation shape motor response execution and inhibition in a Go/NoGo (GNG) task. In Experiment 1, 199 participants were randomly assigned to mere co-presence, evaluative observation, or control. Mere co-presence slowed Go responses and reduced self-reported concentration relative to both other groups without affecting Go accuracy or the NoGo commission error rate relative to control. Only in this group was slower responding associated with greater perceptual sensitivity (d′), suggesting compensatory slowing. By contrast, evaluative observation reduced the NoGo commission error rate and increased d′ relative to both other groups without affecting Go performance relative to control. Experiment 2 used a within-subject event-related potential (ERP) design (N = 44) and replicated the lower NoGo commission error rate and higher d′ under evaluative observation without affecting Go performance. Additionally, evaluative observation produced evaluation-related affective costs—increased evaluative pressure and anxiety—that predicted smaller d′ gains and attenuated its benefit in mediation analyses. Eletrophysiologically, evaluative observation attenuated NoGo-N2 and NoGo-P3 amplitudes without affecting Go components, suggesting that enhanced Go–NoGo discrimination facilitated inhibition by reducing early conflict-monitoring and later reactive-control demands. These findings suggest two dissociable pathways through which distinct forms of social presence shapes motor control.