The Trolley Dilemma vs. the Footbridge Dilemma

J.D. Greene and his associates, in their 2001 article for Science, "An fMRI Investigation of Emotional Engagement in Moral Judgment," compared "the Trolley Dilemma" and "the Footbridge Dilemma" through a pair of experiments aimed at visualizing the possible differences in reactions to the moral-personal and moral-impersonal quandries. The dilemmas come from a common query of moral philosophers, in which the acceptance of two choices is recorded: 1) if you could switch the path of a trolley to save 5 people, while knowing that it would still hit one person, would you do it? and 2) if this same trolley was barreling toward 5 people, but you could stop the trolley by shoving a person into its path from an overhead footbridge, would you do it? The results are the same, 5 people are saved while 1 is killed, but the responses to such dilemmas differ greatly. Those tasked with changing the trolley's path to save 5 people will, for the majority, say this the better option. However, being charged with pushing someone in the path of the trolley to save 5 is seen as unacceptable.

The authors tested these dilemmas in two ways: 1) they tested for differences in brain activity in typical locations for both emotional responses and motor planning responses; and 2) they tested the response times of participants. In the first test, they found that the moral-personal choice, in which they had to push someone off the footbridge, registered highly in the emotional locations of the brain, whereas the impersonal choice, changing the trolley's path, did not elicit an equal emotional response. And for the 2nd test, they found that the response time, for those saying that pushing someone into the trolley's path, to save another 5 people, was the acceptable option, was much slower than those saying it was unacceptable. The authors theorize that the delay is in the participants' arguing internally about the emotional costs of pushing someone to their death to save another 5 people.

The findings suggest that there is a separation in the brain's response depending on the extent to which the respondent is personally involved in the dilemma.

Implications could broaden understanding of how to teach empathy and compassion, particularly in discussing foreign experiences or rare occurrences.

Joshua D. Greene currently directs the Greene Moral Cognition Lab in Cambridge, MA.