A psychologist investigated the effect of environmental cues on cooperative behavior in a shared student kitchen. Over a six-week period, a sign-up sheet for cleaning duties was posted. In the first three weeks, the wall behind the sheet featured a poster showing a pair of wide, attentive human eyes. In the remaining three weeks, the poster was replaced with an image of a generic landscape. The researcher found that the number of students volunteering for cleaning duties was significantly higher when the poster of the eyes was present compared to when the landscape poster was present.