The seminal research on delayed gratification – the now-famous "marshmallow experiment" – was conducted by Walter Mischel in the 1960s and 1970s at Stanford University. Mischel and his colleagues were interested in strategies that preschool children used to resist temptation. They presented four-year-olds with a marshmallow and told the children that they had two options: (1) ring a bell at any point to summon the experimenter and eat the marshmallow, or (2) wait until the experimenter returned (about 15 minutes later), and earn two marshmallows.