EEG evidence of decisions under social influence and ambiguity.

Conformity, the tendency to adapt behavior under social influence, is largely influenced by informational ambiguity and group pressure. While previous research has extensively examined these factors independently, their joint influence and underlying neural mechanisms remain poorly understood. This study employed a gender judgment task combined with electroencephalography to investigate how information ambiguity and group pressure interact to shape conformity. Participants (male and female) were exposed to varying levels of information ambiguity (clear vs. ambiguous) and group pressure (none, low, high) while making gender judgments based on auditory and visual stimuli. Behavioral results revealed significant main effects of both factors: ambiguous information increased conformity compared to clear information, and higher group pressure amplified this effect. Additionally, a significant interaction indicated that group pressure exerted a stronger influence on conformity under ambiguous conditions. EEG data showed that ambiguous information elicited more negative N2, N450, and late positive potential (LPP), while high pressure elicited more negative feedback-related negativity (FRN) and reduced P3 amplitudes. Time-frequency analysis revealed increased theta-band power under ambiguity, alongside heightened theta and alpha power under high pressure. Multivariate pattern analysis (MVPA) demonstrated that EEG activity during both gender judgement and feedback stages predicted conformity, with earlier predictive signals during feedback processing. Regression analyses further confirmed that theta-band power differences under ambiguous versus clear conditions, combined with theta-band differences under high versus no group pressure, significantly predicted the incidence of conformity. These findings elucidate the neural mechanisms underlying conformity, highlighting the interplay between information ambiguity and group pressure in shaping decision-making.