"Tononi's theory goes roughly like this: consciousness is not an all-or-nothing property but instead exists on a gradient and can be quantified. Consciousness arises from complex systems that can take on many configurations where the information generated by the whole above and beyond its parts. Drawing on information theory, Tononi has devised a set of equations that capture an organism's levels of differentiation (the ability to distinguish many states) and integration (communication across the system). His final measure for the degree of consciousness -- a single number -- is denoted by the Greek letter phi. But I haven't yet told you the most remarkable part about this book: It's not a science text, it's a narrative fiction in the style of Dante's "Divine Comedy" in which the protagonist is nudged toward insight by a helpful interlocutor." - Adriano

seemingly difficult question: what are the necessary and sufficient conditions for a physical system to generate experience? see Tononi (2008), Integrated Information in Discrete Dynamical Systems: Motivation and Theoretical Framework, PLoS Computational Biology 4(6):e1000091, http://goo.gl/vO3Rl PDF for details on phi. \\ Christof KOCH (2009 SciAm) offers an informal exposition http://goo.gl/xiuUz of the Integrated Information Theory of consciousness. - Adriano

Tononi also has a manifesto published as "Consciousness as Integrated Information" (2008) in Biological Bulletin 215(3):216-242, http://goo.gl/CQz8V PDF. "We need to perform a prohibitively large set of computations. One would need to perturb a system in all possible ways and use Bayes’ rule to keep track of the probabilities of the previous states given the current output, and then calculate the relative entropy between the potential and the actual distributions. Moreover, this must be done for all possible subsets of a system (to find complexes) and for all combinations of connections (to obtain the shape of each quale). Finally, the calculations must be repeated at multiple spatial and temporal scales to determine what is the optimal grain size, in space and time, for generating integrated information. It goes without saying that these calculations are presently unfeasible for anything but the smallest systems." - Adriano

"A highly conscious experience is a discrimination among trillions of alternatives—it specifies that what is the case is this particular state of affairs, which differs from a trillion other states of affairs in its own peculiar way, and in a way that is imbued with evolutionary value. Equivalently, one can say that a quale of high Φ represents a discrimination that is extremely context-sensitive, and thus likely to be useful. Experience is choice, and a highly conscious choice is a choice that is both highly informed and highly integrated." --ibid. in closing. - Adriano