Individual differences in speed-accuracy trade-off influence social decision-making in dyads.

Speed-accuracy trade-offs are a fundamental aspect of decision-making, requiring individuals to balance collecting more information against making faster decisions. Although speed-accuracy trade-offs have been studied at the individual level, their role in human decision-making in social settings remains poorly understood-even though faster, and possibly more error-prone, decisions often have more social influence than slower decisions. We examined how individual differences in speed-accuracy trade-off preferences shape decision-making in pairs, using an interactive online experiment and drift-diffusion modelling. Participants first performed a perceptual task alone, allowing us to estimate their individual drift rates and decision thresholds, the key cognitive determinants of speed-accuracy trade-off preferences. They then performed the task in pairs, sharing decisions in real-time. Pair accuracy depended on the faster (and thus more error-prone) member, and not on the slower (but more accurate) member. Social decisions were not worse than individual ones because faster members increased their thresholds in the social condition and became more accurate, while slower members incorporated less social information. These findings show that individuals adjusted their social information use to the speed-accuracy trade-off preferences of their partners, highlighting the importance of such individual differences for understanding social behaviour.