  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.
