Csikszentmihalyi, Mihaly. Flow: The Psychology of Optimal Experience. New York: Harper and Row, 2009.
In his book, Csikszentmihalyi presents some of his own research regarding when human beings experience optimal flow states. He concludes that when people are engaged in activities that are low cost yet mentally stimulating they are at their happiest and are engaged in a focused state of flow thereby. He explores what defines a flow state and what one’s consciousness does to enter into it. He also presents helpful research by colleagues, such as Dr. Jean Hamilton (visual perception and cortical activation), as well as Dr. Jerome Singer (daydreaming and mental imagery).