Accurate decisions about whether to trust someone are critical for adaptive social behavior. Previous research into trustworthiness decisions about face stimuli have focused on individuals. Here, decisions about groups of people are made cumulatively on the basis of sequences of faces. Participants chose to either increase or withdraw an initial investment in mock companies based on how trustworthy the company representatives (face stimuli) appeared. Companies were formed using participant trust ratings from the previous week, to create strong trustworthy, weak trustworthy, weak untrustworthy, and strong untrustworthy companies. Participants made faster, more accurate decisions for companies carrying stronger evidence (e.g., faces rated more extremely). Companies with more extreme ratings yielded faster decisions for untrustworthy than trustworthy companies, consistent with a negativity bias. Electrophysiological data revealed that amplitude of the P1 and P3 ERP components, linked to attentional processes, were largest for strong trustworthy faces. This suggests that evidence counter to bias draws special attention. In addition, the first face representing each company provoked larger amplitude P1, P3, and LPP than subsequent faces. This result suggests that when making social decisions about groups of people, the first person one meets receives the most attention.
Keywords: Evidence accumulation; event-related potentials; face perception; trustworthiness.