In order for Artificial Intelligence (AI) to be realized, a comprehensive understanding of general intelligence (human intelligence) must be achieved, but not necessarily replicated. What is intelligence, anyway? Eliezer S. Yudkowsky states: In humans, intelligence is a brain with a hundred billion neurons and a hundred trillion synapses; a brain in which the cerebral cortex alone is organized into 52 cytoarchitecturally distinct areas per hemisphere. Intelligence is not the complex expression of a simple principle; intelligence is the complex expression of a complex set of principles. Intelligence is a supersystem composed of many mutually interdependent subsystems - subsystems specialized not only for particular environmental skills but for particular internal functions.
He postulates that there are no simple set of rules we can use to define the complex process of thinking abstractly and further argues that unlike physics, the field of AI cannot succeed by condensing complexity into relatively simple expressions.
Read Yudkowsky's Levels of Organization in General Intelligence to learn more about the application of general intelligence in AI. Overall, it's an interesting read.