Imagine you’re standing on a footbridge over some trolley tracks. Below you, an out-of-control trolley is bearing down on five unaware individuals standing on the track. Standing next to you is a large man. You realize that the only way to prevent the five people from being killed by the trolley is to push the man off the bridge, into the path of the trolley. His body would stop the trolley, saving the lives of the five people further down the track.

What would you do? Would you push the man to save the others? Or would you stand by and watch five people die, knowing that you could have saved them? Regardless of which option you choose, you no doubt believe that it will reflect your deeply held personal convictions, not trifles such as your mood.

Well, think again. In a paper published in the March edition of the journal Cognition, a group of German researchers have shown that people’s mood can strongly influence how they respond to this hypothetical scenario. Though this general observation is well-known in the literature on moral judgments and decision making, the current paper helps to resolve a question which has long lurked in the background. That is, how does this happen? What is the mechanism through which moods influence our moral decisions?

Early research showed a difference between personal moral decisions, such as the footbridge problem above, and impersonal moral decisions, such as whether to keep money found in a lost wallet. Areas of the brain usually characterized as responsible for processing emotional information seemed to be more strongly engaged when making these personal as opposed to impersonal moral decisions, they found. These scientists concluded that emotions were playing a strong role in these personal moral judgments while the more calculating, reasoning part of our mind was taking a siesta.

Unfortunately, given the various shortcomings of previous investigations on this particular topic, there are a variety of other explanations for the observation that emotions, or the more general emotional states known as moods, affect how people may respond to the footbridge scenario.

For example, moods could influence the thought process itself. This is the “moral thought” hypothesis: just as something like attention may change our thought process by biasing how we perceive two choices, mood could also bias our thought process, resulting in different patterns of moral thinking. This is different from the “moral emotion” hypothesis, which suggests that emotions directly change how we feel about the moral choice. That is, our good mood could making us feel better (or worse) about potentially pushing, and therefore more (or less) likely to do it. Resolving this ambiguity with neuroimaging studies such as the one detailed above is difficult because of fMRI’s low temporal resolution – a brain scan is similar to taking a camera with the exposure set to a couple of seconds. This makes it difficult to faithfully capture events which happen quickly, such as whether moods change the experience of the decision, or if they directly influence the thought process.

To test these competing ideas, participants were first put into a specific mood by listening to music and write down an autobiographical memory. Those in the positive mood condition listened to Mozart’s Eine Kleine Nachtmusic and wrote down a positive memory, while those in the negative mood condition listened to Barber’s Adagio for Strings, Opus 11 and wrote down a negative memory. The participants in the neutral mood condition listened to Kraftwerk’s Pocket Calculator and wrote about a neutral memory.

After this mood induction procedure, participants were then presented with the trolley scenario. Some participants were asked: “Do you think it is appropriate to be active and push the man?” while others were asked “Do you think it is appropriate to be passive and not push the man?”.

Participants in a positive mood were more inclined to agree to the question, regardless of which way it was asked. If asked if it was okay to push, they were more likely to push. If asked if it was okay not to push, they were more likely to not push. The opposite pattern was found for those in a negative mood.

If mood directly changed our experience of potentially pushing — the moral emotion hypothesis — then putting people in a positive mood should have made them more likely to push, no matter how the question was asked. The ‘moral thought’ hypothesis, on the other hand, accounts for these results quite nicely. Specifically, it is known from previous research that positive moods validate accessible thoughts, and negative moods invalidate accessible thoughts. So, for example, if I ask you if it’s okay to push, you will begin to consider the act of pushing, making this thought accessible. If you’re in a positive mood, that mood acts on this thought process by making you more likely to feel as though this is an acceptable behavior – it validates the thought of pushing. On the other hand, if I were to ask if it is okay to not push, the positive mood should validate the thought of not pushing, leading you to feel like not pushing is an acceptable behavior. Negative mood, which invalidates accessible thought, has a parallel effect, but in the opposite direction. Thus, this idea fits well with the observed pattern of results in this experiment.

These findings raise some further questions, some of which psychologists have been attempting to answer for a long time. Emotions and logical thought are frequently portrayed as competing processes, with emotions depicted as getting in the way of effective decision-making. The results here are another demonstration that instead of competing, our emotions and our cognitions interact and work closely to determine our behaviors. In fact, some researchers have recently begun to suggest that the division between these two is rather tough to make, and there may not actually be any meaningful difference between thought and emotion. After all, if moods and emotions play a fundamental role in information processing, what differentiates them on a functional level from other basic kinds of cognitive processes, such as attention or memory? This paper obviously doesn’t resolve this issue, but it is certainly another piece of the puzzle.

It would also be exciting, as the authors say, to see how more specific emotions might influence our moral decision-making. Anger and sadness are both negative emotions, but differ in important ways. Could these subtle differences also lead to differences in how we make moral judgments?

This paper demonstrates that our professed moral principles can be shifted by subtle differences in mood and how a question is posed. Though there are plenty of implications for our daily lives, one that arguably screams the loudest concerns the yawning gap between how humans actually think and behave, and how the legal system pretends they think and behave. The relative rigidity of western law stands in stark contrast to the plasticity of human thought and behavior. If a simple difference in mood changes how likely one person is to throw another over a footbridge, then does this imply that the law should account for a wider variety of situational factors than it does presently? Regardless of how you feel, it is clear that this paper, and behavioral science in general, should contribute to the decision. Having a legal system based on reality is far preferable to one based on fantasy.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas.