CONCEPT
Integrated Information Theory
Tononi's mathematical framework that identifies consciousness with integrated information — beginning from the phenomenology of experience and deriving the physical structure a system must have to instantiate it.
Integrated Information Theory (IIT) is Giulio Tononi's three-decade attempt to transform consciousness from a domain of qualitative description into a domain of mathematical measurement. Its foundational move is methodological inversion: rather than starting with the brain and asking what it does to produce experience, IIT starts with experience itself and asks what properties a physical system must have to be identical to it. From five phenomenological axioms — existence, composition, information, integration, and exclusion — the theory derives corresponding postulates about physical cause-effect structure. The result is a quantity, phi, which the theory claims is not a correlate of consciousness but consciousness itself, expressed as a number. IIT is substrate-independent: its predictions apply equally to biological and artificial systems.
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IIT emerged from Tononi's dissatisfaction with the dominant neuroscientific strategy of searching for the neural correlates of consciousness. Correlates, Tononi argued, are not causes. Knowing that the cerebral cortex is active during conscious experience and