In a 1990 experiment examining the psychological effect of these constructs, students littered less when they saw one piece of trash on the ground than no trash on the ground. These constructs require the existence of first-order empirical beliefs, and transform mixed-motive games into cooperative ones, according to Cristina Bicchieri. The now disgraced Dan Ariely used the example of paying your mom for Thanksgiving dinner to differentiate the ■END■