Neuroscientist Giulio Tononi of the University of Wisconsin-Madison developed one of the most promising theories for consciousness, known as integrated information theory.
Understanding how the material brain produces subjective experiences, such as the color green or the sound of ocean waves, is what Australian philosopher David Chalmers calls the “hard problem” of consciousness. Traditionally, scientists have tried to solve this problem with a bottom-up approach. As Koch put it, “You take a piece of the brain and try to press the juice of consciousness out of [it].”
But this is almost impossible, he said. In contrast, integrated information theory starts with consciousness itself, and tries to work backward to understand the physical processes that give rise to the phenomenon, said Koch, who has worked with Tononi on the theory.
The basic idea is that conscious experience represents the integration of a wide variety of information, and that this experience is irreducible. This means that when you open your eyes (assuming you have normal vision), you can’t simply choose to see everything in black and white, or to see only the left side of your field of view.
Instead, your brain seamlessly weaves together a complex web of information from sensory systems and cognitive processes. Several studies have shown that you can measure the extent of integration using brain stimulation and recording techniques.
The integrated information theory assigns a numerical value, “phi,” to the degree of irreducibility. If phi is zero, the system is reducible to its individual parts, but if phi is large, the system is more than just the sum of its parts.
This system explains how consciousness can exist to varying degrees among humans and other animals. The theory incorporates some elements of panpsychism, the philosophy that the mind is not only present in humans, but in all things.
An interesting corollary of integrated information theory is that no computer simulation, no matter how faithfully it replicates a human mind, could ever become conscious. Koch put it this way: “You can simulate weather in a computer, but it will never be ‘wet.'”
The above is also from Tanya Lewis on “Scientists closing in on theory of consciousness” (livescience.com)