A person stands trans xed before a Mark Rothko abstract painting oblivious to everything else. Embedded in this scene are questions that strike at the very heart of this book. What is the sensation being experienced? If the color or form of the painting were altered slightly, would the experience be the same? Why do some visitors to the museum glance at the same painting and shrug their shoulders before being absorbed by a Cezanne landscape or a Rembrandt portrait? Why do visitors bother to gaze at paintings at all? What is the nature of the reward that compels them to travel distances, pay entrance fees, and negotiate crowds to stare at pieces of canvas? What, if anything, distinguishes this rewarding experience from the pleasure of gazing at an attractive person or from the anticipation of a good meal?