PSYCH 4320 / COGST 4310 / BioNB 4330

Consciousness and Free Will

Theme III

  Week 7: the Information Integration Theory, II

Week 7: the Information Integration Theory (IIT): v.3

questions from Week 5, revisited

"The first-person exercise we have just conducted yields a minimal definition of the self as the perceptual egocenter of sensory consciousness and, BY EXTENSION, OF ALL AWARENESS."

What about bees? Nematodes?

Is completely self-less awareness possible? And if yes, what neural — or, better, COMPUTATIONAL — processes are necessary and sufficient for it?

IIT: axioms

IIT: postulates

To parallel the phenomenological axioms, IIT posits a set of postulates. These list the properties physical systems must satisfy in order to generate experience.

IIT: postulates (mechanisms)

The next three postulates, information, integration, and exclusion, apply both to individual mechanisms and to systems of mechanisms.

IIT: postulates (systems of mechanisms)

IIT: identities

The maximally irreducible conceptual structure (MICS) generated by a complex of elements is identical to its experience. The constellation of concepts of the MICS completely specifies the quality of the experience (its quale ‘‘sensu lato’’ (in the broad sense of the term)). Its irreducibility WMax specifies its quantity. The maximally irreducible cause-effect repertoire (MICE) of each concept within a MICS specifies what the concept is about (what it contributes to the quality of the experience, i.e. its quale sensu stricto (in the narrow sense of the term)), while its value of irreducibility QMax specifies how much the concept is present in the experience. An experience is thus an intrinsic property of a complex of mechanisms in a state. In other words, the maximally irreducible conceptual structure specified by a complex exists intrinsically (from its own intrinsic perspective), without the need for an external observer.

the intrinsic information bottleneck principle

Each mechanism in the system acts as an information bottleneck from the intrinsic perspective: its cause information only exists for the system to the extent that it also specifies effect information and vice versa. While other ways of measuring a mechanism’s cei may also be compatible with the examples shown in Figure 5, the ‘‘intrinsic information bottleneck principle’’ is best captured by defining a mechanism’s cei as the MINIMUM between its cause and effect information.

the minimum information partition (MIP)

Of the many possible ways to partition a mechanism, integrated information is evaluated across the minimum information partition (MIP), the partition that makes the least difference to the cause and effect repertoires (in other words, the minimum ‘‘difference’’ partition).

According to IIT, mechanisms that do not generate integrated information do not exist from the intrinsic perspective of a system, as illustrated in Figure 7.

the exclusion postulate, applied to a mechanism

The exclusion postulate at the level of a mechanism says that a mechanism can have only one cause and one effect, those that are maximally irreducible (MICE); other causes and effects are excluded.

To understand the motivation behind the exclusion postulate as applied to a mechanism, consider a neuron with several strong synapses and many weak synapses (Figure S1). From the intrinsic perspective of the neuron, any combination of synapses could be a potential cause of firing, including ‘‘strong synapses’’, ‘‘strong synapses plus some weak synapses’’, and so on, eventually including the potential cause ‘‘all synapses’’, ‘‘all synapses plus stray glutamate receptors’’, ‘‘all synapses plus stray glutamate receptors plus cosmic rays affecting membrane channels’’, and so on, rapidly escalating to infinite regress. The exclusion postulate requires, FIRST, that only one cause exists. This requirement represents a causal version of Occam’s razor, saying in essence that ‘‘causes should not be multiplied beyond necessity’’, i.e. that causal superposition is not allowed [6]. In the present context this means that only one set of synapses can be the cause for the neuron’s firing and not, for example, both ‘‘strong synapses S1,S2’’ and ‘‘all synapses’’, or an average or integral over all possible causes. SECOND, the exclusion postulate requires that, from the intrinsic perspective of a mechanism in a system, the only cause be the maximally irreducible one.

more on the intuition behind the exclusion principle

Recall that IIT’s information postulate is based on the intuition that, for something to exist, it must make a difference. By extension, something exists all the more, the more of a difference it makes. The integration postulate further requires that, for a whole to exist, it must make a difference above and beyond its partition, i.e. it must be irreducible. Since, according to the exclusion postulate, only one cause can exist, it must be the cause that makes the most difference to the neuron’s output if it is eliminated by a partition – that is, the cause that is maximally irreducible.

what brains do

In IIT, the relationship between the MICS generated by a complex of mechanisms, such as a brain, and the environment to which it is adapted, is not one of ‘‘information processing’’, but rather one of ‘‘matching’’ between internal and external causal structures.