The Integrated Information Theory of Consciousness: An Updated Account

Abstract

This article presents an updated account of the integrated information theory of consciousness (IIT) and of some of its implications. The IIT stems from two phenomenological thought experiments. The photodiode thought experiment shows that every experience is one out of many – it is what it is by differing in its own particular way from a large repertoire of alternatives (information). The camera thought experiment shows that each experience is one – it cannot be decomposed into independent parts (integration). The IIT formalizes these intuitions by arguing that a mechanism in a state intrinsically generates information: it reduces uncertainty by specifying which previous states of a system could have caused its current state and which could not (an actual repertoire). A set of mechanisms generates integrated information to the extent that the information they generate cannot be partitioned into that generated within independent parts. Depending on the causal structure of a system, integrated information reaches a maximum at a particular spatial and temporal grain size and among a particular set of elements (a complex). The theory postulates that the actual repertoires within a complex yielding integrated information (an integrated information structure or quale) specify both the quantity and the quality of experience. Furthermore, changes in information integration upon exposure to the environment reflect a system’s ability to match the causal structure of the world. After introducing an updated definition of information integration and related quantities, the article presents some theoretical considerations about the relational structure of concepts within a quale and about the relationship between information and causation. It also explores the relationship between the temporal grain size of information integration and the dynamic of metastable states in the corticothalamic complex. Finally, it summarizes how the IIT accounts for empirical findings about the neural substrate of consciousness, and how various aspects of phenomenology may in principle be addressed in terms of the geometry of information integration.