Making Sense of Consciousness as Integrated Information: Evolution and Issues of IIT

The purpose of this article is to provide an overall critical appraisal of Integrated Information Theory(IIT) of consciousness. We explore how it has evolved and what problems are involved in the theory. IIT is a hypothesis that consciousness can be explained in terms of integrated information. It argues that a number of fundamental properties of experience can be properly analyzed and explained by physical systems' informational properties. Throughout the last decade, there have been many advances in IIT's theoretical structure and mathematical model. In addition, like all hypotheses in the field of science of consciousness, IIT has given rise to several controversies and issues. In this context, a critical survey for IIT is urgently needed. To this end, we first introduce fundamental concepts of IIT and related issues. Thereafter, we discuss major transitions IIT has been through and point out related intra-model issues. Finally, in the last section, some theoretical, extra-model issues involved in IIT's principles are presented. The article concludes by suggesting that, for the sake of future development, IIT should more seriously take metacognitive accessibility to experience.