Moral by default? The dynamic tradeoffs between honesty and self-interest
Humans are often faced with social dilemmas that pit self-interest against honesty, yet questions arise about whether this trade-off reflects spontaneous default response or active suppression of the alternative response. Here, we created two message-sending tasks where decisions involved honesty as truth-telling or dishonesty as untruthful-message-sending. In our pre-registered study, participants joined the message task as the sender, who can send truthful or untruthful messages to earn more money for themselves, thus manipulating the conflict between self-interest and honesty. In experiment 1, we used mouse tracking (MT) to gain insight from movement trajectories and reaction time (RTs) of a forced-choice task with one fair default option. We found that being honest under conflict situations took longer for individuals who had higher self-interest concerns. In experiment 2 with a two-alternative forced-choice design without a default fair option on another sample to test whether self-interest-seeking people would show a similar tendency to lie and how these behavioral patterns correlated with utility and drift-diffusion model (DDM) modeling parameters. We found lower RTs for untruthful responses when self-interest concern was higher. In both experiments, the mixed model of RTs indicated the interest-temptation (i.e., conflict) condition led to a longer RT for truth-telling. These results were also supported by a DDM showing a larger drift rate for untruthful, compared to truthful, responses in conflict trials. Overall, our findings further support the individual difference in moral default, which can be manifested in behavioral indices in decisions.