Would you push one man off a cliff to save five others? It's an odd question… and it's actually one of the questions in the trolley problem, a famous moral dilemma in which we are forced to make a decision that inevitably leads to someone's death. Would you believe it if we told you that your response depends in part on what you’re viewing at the moment you make the decision?

Moral dilemmas and moral choice are largely used in psychology to study the criteria that influence decision-making. The response to these types of questions depends on many factors, such as cultural and individual values and the amount of time given to respond. It's less clear what influence sensory stimuli have on the decision-making process, which we usually believe to be based on rational mechanisms.

In this case, scientists from universities in Sweden, London and California observed the eye movements of participants who had been asked to answer difficult moral questions, such as "Is murder justifiable?" Participants were not aware that their responses were being recorded. When it came time to answer, one of the two responses was displayed at random, and the person was asked to reply at the very moment that his or her gaze fell on the solution.

“The processes that lead to a moral decision are reflected in gaze. However, what our eyes rest on when a decision is taken also affects our choice,” explained Philip Pärnamets, a cognitive scientist at Lund University and co-author of the study: the participants systematically chose the displayed response as being their own.

The study raises many questions about our recent past: what elements contributed to our most recent important decisions? These results also demonstrate how easy it may be to influence the decisions of others, simply by playing with elements in the visual field. More disturbing, this phenomenon occurs without our awareness…