Pencil man (writing_on_paper_is_better)

People who screw up their courage to participate in a study for which they aren't paid, in which they're repeatedly poked with needles, and in which they have only a fifty-fifty chance of getting an active drug are intrinsically motivated to solve their problem. Maybe their reward is only the attention paid to them, the opportunity to respond to questions about how they feel and think. But maybe the mother's kisses that soothe her child's scrapes are "just" a placebo as well.