One of the anonymous reviewers of my book manuscript remarked, with approval, that it contained very little discussion of embodied, extended and enactive (EEE) cognition. Probably this omission stems from my Kantian gut feeling that an explanation of mind and cognition must appeal only to what happens after sensory input hits the senses, and the view that the prediction error minimization (PEM) scheme accomplishes this explanation. But does PEM indeed make the extremely influential current EEE-debates obsolete? Can one buy into PEM and EEE at the same time? This post suggests that PEM is indeed cast in an unfashionable Cartesian and Kantian mould, which is anathema to EEE. Yet, though deeply inferentialist, PEM does give a central role to the body, to some objects, and to action.
According to PEM, perception and cognition arises in a process where an internal model predicts the sensory input and thereby infers the hidden causes of that sensory input. The only thing that matters is the ability to suppress prediction error on average and over time. This means that what matters is a process on the “inside”, between the sensory input and the internal model. The focus is on keeping the sensory input predictable. This can be difficult in a world with many interacting causes that produce twists and turns in the sensory input at many time scales. This difficulty calls for all the statistical PEM-tools, employed in a hierarchical model, as outlined in the previous post.
If all that matters is a relation between sensory input and internal model, then there is little reason to think that things on the “outside” such as the body and specific objects matter to an explanation of the mind. More accurately, the body and things in the environment matter only insofar as they have the potential to influence the flow of sensory input and thus mandate representation in some parameter of the internal model.
The body is hugely important here, since the way we move around in the environment causes massive changes in the sensory input. Therefore we had better be able to form pretty much all our expectations of sensory input conditional on what the body is like and what it is doing. If not then it would be difficult to keep prediction error under control. This means that the mind is ‘embodied’ only in the sense that the body is an internally represented cause of sensory input. In principle the body is no different from other objects that may cause various degrees of havoc to the flow and thus the predictability of sensory input.
This inferential story immediately incorporates action, since action is part of what makes the body move around; perception is thus ‘enactive’ because action causes changes in sensory input. I also think that the mind is ‘extended’ only in the sense that some inferred external objects are associated with high precision prediction error, in particular in our inferences about action. Though more is needed to fill this out, I think the wholly internal PEM story can account for the intuitions and cases that drive the EEE-views.
The upshot is a very deflated conception of the role of body, objects and action (including of self and of other people). All this is just representations that we harbor because they best explain away the sensory input. If some other representation could better explain away sensory input, then we would jettison the old ones immediately (to illustrate how fickle our representations are recall the study linked to in the first post, where Bryan and I show how readily we experience the world as having supernatural phenomena). I rather like this solipsistic, minimalist, opportunistic, almost nihilist landscape of our mental lives—Scandinavian noir for the mind. Andy Clark, on the other hand, sees PEM as much more amenable to some (but not all) the EEE trends; in Andy’s more sunny perspective PEM is a more ‘jazzy’, rich framework for understanding our fluent interactions with the world.
My interpretation of PEM is driven by the fact that PEM has to be strongly internalist, simply because PEM must be inferential. There must be something doing the inference and something, on the other side of an ‘evidential boundary’, which is being inferred. The more of the occurrent evidence that the agent’s model can explain away the more the agent gains evidence for itself—creatures are in other words self-evidencing. There is growing awareness that this evidential boundary is a Markov blanket for the internal states, such that the behavior of the brain can be understood once the brain’s sensory and active states are known. This of course allows Cartesian skepticism, a total seclusion from the external world: we have an epistemically motivated sensory veil and we have even said that the evidence for the agent’s existence is the model’s prowess at anticipating the activity at its sensors. Truly, I think (=minimize prediction error), therefore I am. (See papers by Friston that Bryan linked to in an earlier post, as well as this one; much of this is developed in my paper here).
All of this suggests that PEM comes with a principled way of drawing the boundary between mind and world, and a clear agenda for understanding the mind in neurocentric terms. Importantly, PEM appropriates body, special objects, and action into this internalist scheme. So it is anti-EEE without ignoring the explanatory challenges posed by the EEE-literature.
Having said all this, PEM also sees us as embedded in the causal structure of the world. We are physical structures in the world, who for some span of years manage to use action to maintain our bodily integrity and thus withstand dispersion. If it wasn’t for the causal impact of the world on our senses PEM would have no purpose. In this setting, PEM is aligned with older notions of self-organisation as well as newer, enactivist notions of autonomy, autopoeisis, and self-enabling (see Evan Thompson and co-authors). What intrigues me is that here we need a marriage of a strongly anti-inferentialist, anti-internalist EEE-style view with the unapologetically inferentialist and internalist PEM. I suspect a profound conception about the mind will come to light once we figure out how to reconcile these views.