On a variation of Trolley's problem. How to explain the survey's results? It is not long since a friend of mine reported about an experiment they would do in their philosophy class, or rather, in their philosophy classes. At that time, his and the parallel class were dealing with the problems in regards to Utilitarianism.

The teacher then proposed in class A the following problem (see Trolley Problem)


  You see a runaway trolley moving toward four tied-up people lying on the main track. You are standing next to a lever that controls a switch. If you pull the lever, the trolley will be redirected onto a side track, and the four people on the main track will be saved. However, there is a single person lying on the sidetrack. You have two options:
  
  
    
    Do nothing and allow the trolley to kill the four people on the main track.
    Pull the lever, diverting the trolley onto the side track where it will kill one person.
    Which is the more ethical option? Or, more simply: What is the right thing to do?
    
  


Sidenote: The only thing you know about these people is that they're all more or less the same age. Nothing else (so there are no criminals, murders or saints to be taken into consideration).

The teacher then asked the pupils what they would do. The results were


29 would pull the lever. They argued that, on equal terms, letting one person die is worth if you can save four lives (4>1).
1 claimed, he wouldn't do anything, because he believed in destiny.


Now the teacher proposed another problem in the parallel class B, which goes as follows


  One man enters a hospital - let's call him John - because he has injured his arm. Nothing dangerous, but it requires disinfection. Coincidentally, in the same hospital, four patients are about to die. They need (urgently) respectively these organs: a heart, a liver, two kidneys, and lungs.
  
  After some tests, it turns out, that John's organs aren't only in perfect conditions for a transplant but are also compatible with the four patients mentioned previously.
  
  Assume now that the hypothetical transplants would all succeed and that John is the only possibility for those four patients to survive. You have two options:
  
  
    
    Let John go home after disinfection and allow the four patients to die.
    Arrest John and take his organs in order to save the four patients' lives. John dies.
    
  


Sidenote: Again, the only thing you know about these people is that they're all more or less the same age. Nothing else (so there are no criminals, murders or saints to be taken into consideration).

Surprisingly, a survey revealed the following results


23 would let John go home, even if the four patients die. They argued that John should decide whether to sacrifice for the benefit of the other patients.
7 would remove John's organs - and therefore kill him - in order to save the other patients' lives. They believed that four lives are, on equal terms, more value than one.


The teacher then brought both classes together and let them compare their viewpoints regarding the respective situations. Most of them agreed with the decisions, their colleagues from the parallel class had taken until one student noticed


  "We are actually dealing with the same situation. It does not matter wheter railway tracks or a hospital: this is just the context and it should not influence the final decision. The problem reduces to deciding wheter for people should live or only one, but not both of them."


Last, but not least, my question: How can you explain psychologically that, even though the students had to address the same question, the answers were dramatically different?
The two problems might seem to be equivalent but they aren't - in the "John" scenario those advocating not to arrest John and harvest his delicious organs are pointing out that:


  that John should decide whether to sacrifice for the benefit of the other patients.


This is showing that the problems aren't equivalent because John has a choice to sacrifice himself - he could turn to the docs and say - "Right! Knock me out and cut me up!"

In the trolley problem however the one doesn't have the choice to sacrifice themselves for the many, when deciding between forcing John to be an organ donor and letting the others die the ethical dilemma is about removing John's agency. To make the problems equivalent you would have to modify the trolley problem such that the "one" person also had access to a lever to divert the trolley such that it would kill them (and the knowledge of what pulling that lever would do).

Essentially the "John" scenario could be considered similar to the "stranger on a footbridge" variant of the Trolley Problem:


  In another version of the problem, the trolley, as before, is about
  to kill five people. This time, however, you are not standing near the
  track, but on a footbridge above the track. You cannot divert the
  trolley. You consider jumping off the bridge, in front of the trolley,
  thus sacrificing yourself to save the imperiled people, but you realize
  that you are far too light to stop the trolley. Standing next to you,
  however, is a very large stranger. The only way you can stop the
  trolley killing five people is by pushing this large stranger off the
  footbridge, in front of the trolley. If you push the stranger off, he will
  be killed, but you will save the other five.


-Ethics and Intuitions, Peter Singer 2005

As with the "John" case the majority vote not to kill the poor fat stranger and instead allow the hapless majority to die.

As to why the two different problems provoke such different responses, Dr Joshua Greene examined this in his doctoral thesis The Terrible, Horrible, No Good, Very Bad Truth about Morality and
What to Do About it and proposed that the difference was driven by a difference in emotional response.

As he put it:


  Because people have a robust, negative emotional response to the personal violation proposed in the footbridge case they immediately say that it’s wrong... At the
  same time, people fail to have a strong negative emotional response to the relatively impersonal violation proposed in the original trolley case, and therefore revert to the most obvious moral principle, ‘‘minimize harm,’’ which in turn leads
  them to say that the action in the original case is permissible


Greene tested this theory using an fMRI in An fMRI Investigation of
Emotional Engagement in Moral
Judgment and the results seem to suggest that the initial response to the stranger-on-a-footbridge variant is indeed an emotional one (based on activity seen on the fMRI in different areas of the brain) and it is this that leads to the difference in responses:


  The trolley and footbridge dilemmas
  emerged as pieces of a puzzle for moral philosophers: Why is it acceptable to sacrifice one
  person to save five others in the trolley dilemma
  but not in the footbridge dilemma? Here we
  consider these dilemmas as pieces of a psychological puzzle: How do people manage to conclude that it is acceptable to sacrifice one for the
  sake of five in one case but not in the other? We
  maintain that emotional response is likely to be
  the crucial difference between these two cases.
  But this is an answer to the psychological puzzle, not the philosophical one.