... incentives will have a detrimental effect ... -- ...
when the task is interesting enough for subjects that
the offer of incentives is a superfluous source of motivation ... -- ...
when the solution to the task is open-ended enough that the
steps leading to the solution are not immediately obvious ... -- ...
this reduces the requirement that the task be inherently attractive
and have a heuristic solution ...
life(s)
/ closure(s)
/ reflect(s)
/ fight(s)
/ cost(s) of reward(s)