First off, how would you determine whether an individual listens to their heart or not,

At the moment by observing and checking whether specific qualia are there. If I really wanted to make the proof in numbers, that would require that I systematically calibrate my own perception first and determine sensitivity and specificity of my perception of other people.

I'm also still a person who's fairly intellectual. There are people with better perception than myself and getting them to do the assessing might be better.

Having a way to get that data via a more automated process that doesn't need a perceptive human would also be nice. At the moment I however have no clear idea about how to go about measuring or the necessary financial resources to finance that kind of research.

how do you know that individuals who listen to their hearts don't engage in such antisocial behaviors?

A mix of more theoretical thinking and practical observation of the behavior of people with whom I'm interacting changes when the qualia I'm perceiving suggests that the locus of their attention within their body changes.

I would regard this as a highly extraordinary claim demanding commensurately extraordinary evidence,

I understand that's an advanced claim. At the moment I'm more concerned with making clear what the claim is than proving it.

If I say that Harry is not going to kill people if he listens to Hufflepuff but might kill if he listens to Slytherin, would that be a strange claim for you? If I say people who always listen to Hufflepuff don't go on killing sprees would that seem strange to you? Most people you know don't have the ability to mentally commit to 100% listen to Hufflepuff in every decision that they make in their lifes.

If I remember right Eliezer uses those different persona because it's popular in systematic therapy to do so and someone he knows taught him that thinking that way can be useful. Those persona have a different quality than organs that can be perceived kinesthetically but they are not that different.

Lastly it's useful to keep in mind what extraordinary claim needing extraordinary evidence can lead to. If you take it too far it shuts down people from saying what they honestly believe and instead let's them argue beliefs that they don't fully stand behind.

We all have many beliefs that come out of personal experience and not from reading papers. There are areas where the personal experiences differs massively. In those cases we don't get certainity about what's true when someone else tells us about how he thinks the world works. Simply understanding the models of other people is still be useful because then you might use that model sometime in the future when it explains something you see better than your other mental models.