The brain before the herd: Pre-Decision EEG prediction of herd-consistent investment choices among bilingual investors.

This study examines whether pre-decision electroencephalographic (EEG) activity provides incremental information for explaining and predicting herd-consistent investment choices when social and fundamental signals conflict. A controlled 2 × 2 × 2 × 2 within-participant factorial experiment involving 80 English-Mandarin bilingual Chinese investors who met a predefined English-proficiency threshold equivalent to IELTS 6.5 or TOEFL iBT 80 and had prior experience in U.S. equity markets manipulated language, information format, social-media sentiment, and information consistency. Herd-consistent choice was conservatively defined as alignment with the social signal when it contradicted fundamental information. Behavioural and single-trial EEG responses were analysed using mixed-effects models, while machine-learning models were evaluated through nested participant-disjoint validation. The findings indicate that Mandarin-language presentation and short-form financial information are associated with greater conformity to social signals under informational conflict. Conflict between social and fundamental information also elicits stronger frontal-midline theta activity, consistent with heightened demands on cognitive control and conflict monitoring before choice. Pre-decision P300 and theta provide distinct predictive information beyond contextual and participant characteristics, indicating that attentional updating and conflict processing contribute differently to subsequent herd-consistent decisions. These findings support a process-based account of investment conformity in which information architecture, social influence, and pre-decision neurocognitive processing jointly shape herd-consistent choices.