There is one issue about how the researchers attempted to answer
the research question. Strictly speaking, schadenfreude is
independent of the observer’s feelings toward the actor. I expect
that the game was intended to introduce a control condition, but to
create a distinction between viewing the actor as fair or unfair
does not really perform the role, since the control condition would
be ambivalence (a neutral condition) towards the actor, rather than
like or dislike. Effectively, they’ve ended up testing for
neurological evidence of vengefulness or a sense of justice
(depending on how you look at it) rather than schadenfreude.