To simulate or not: the mechanistic underpinnings of predicting the decisions of other people

Sequential sampling models (SSM) assume that decisions for oneself are made by accumulating evidence for the available options, until the choice of one option has been triggered. As such, it seems plausible that predicting the decisions of another individual could be achieved similarly, by simulating the other person’s evidence accumulation process with one’s own cognitive mechanisms – the ‘simulation hypothesis’. Although SSMs have been successfully used to describe predicted decisions of other agents, that in itself is insufficient evidence in support of the simulation hypothesis. However, one concrete implication of the hypothesis is that, if people use their own mind to simulate and predict the decisions of others, then biasing an individual’s own decision-making process should result in a corresponding bias when they make predictions. To test this, we first biased participants’ risk perception (n = 172) by adapting them to a high-risk/low-risk context when they made decisions for themselves, and subsequently asked them to predict the decisions of a risk-seeking and risk-averse (hypothetical) agent in a medium-risk context. On average, participants in the high-risk adaptation group predicted a more risk-accepting behaviour than those in the low-risk group, indicating that the predicted decisions were made with participants’ own biased decision-making system - consistent with the simulation hypothesis. Surprisingly, this effect was only present during prediction for the risk-averse, but not risk-seeking agent, suggesting that the mechanisms of prediction may depend on the specific characteristics (e.g., similarity) of the other person. We also fit our data with a version of the drift diffusion model devised to account for risky decisions, to understand how the seemingly different mechanisms of prediction across agents are captured in the SSM framework.