Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 11

Ema Sullivan-Bissett

Welcome to the Philosophy of Mind and Psychology Reading Group hosted by the Philosophy@Birmingham blog.

This month, Ema Sullivan-Bissett introduces chapter 11 of Jakob Hohwy’s The Predictive Mind (OUP, 2013). Ema is a Research Fellow on Lisa Bortolotti’s ERC-funded project PERFECT, in the Department of Philosophy at the University of Birmingham.

Chapter 11 - The Fragile Mirror of Nature
Presented by Ema Sullivan-Bissett

In chapter eleven Hohwy seeks to challenge background beliefs we hold about the nature of our body, and characterizes us as ‘fundamentally fragile prediction error minimizing machines’ (p. 224). The fragility of the perceptual system is what is to be explicated in this chapter.

Hohwy starts by setting up a contrast between his prediction error minimization view of perception, and the bottom-up view. The latter casts us as ‘passive receivers of sensory input’, which does not require of us that we interpret such input making use of relevant background beliefs. Such a view is, of course, ‘fundamentally in stark contrast to the prediction error minimization idea’ (p. 225).

Philosophy of Mind and Psychology Reading Group -- Predictive Mind chapter 10

Welcome to the Philosophy of Mind and Psychology Reading Group hosted by the Philosophy@Birmingham blog. This month, I am introducing chapter 10 of Jakob Hohwy's The Predictive Mind (OUP, 2013).


Chapter 10 - Perceptual Unity in Action
Presented by Lisa Bortolotti

In this chapter, Hohwy attempts to provide answers to two key questions about perceptual unity by relying on the prediction error minimisation (PEM) model. This is part of the project of showing that the model can account for all the core characteristics of conscious experience, such as having a first-person perspective, being cognitively penetrable, being subject to illusions, etc.

(1) Why do the elements of conscious unity hang together?
(2) Why is there one perceptual state subsuming all other ones?

Tim Bayne (2010, page 75) endorses the "unity thesis", i.e. the idea that conscious states of any subject of experience at any one point in time will occur as the components of a single total phenomenal state, a unitary phenomenal field. Hohwy agrees with Bayne that the unity thesis is true and claims that it is an important (but contingent) feature of consciousness. His task is to explain the unity thesis (as it applies to conscious perception) via the PEM mechanism.

In PEM we switch from seeing a coffee shop and feeling thirsty to making a decision about whether to buy a coffee in the shop or go home and have a glass of water (this is Hohwy's example of a switch from perceptual to active inference as described in previous chapters of the book). The switch involves making many predictions on the basis of different hypotheses and evaluating them in the light of contextually relevant considerations (e.g., money, daily intake of caffeine, time) in order to make a decision and act. What we do as agents who are limited to do one thing at a time is to select one hypothesis as "the best prediction error minimizer". This delivers one perceptual field, and no more.

To answer questions (1) and (2), in Hohwy's words, "perception is unified because it is based on hypotheses in a causally structured hierarchical model". Creatures like us can use only one hypothesis at the time to "sample the world" and make decisions about what to do. Building bridges with the work of Susan Hurley (1998, page 3) on the link between consciousness and action, Hohwy claims that "there would be no need for unity if there were no agency". That said, he rejects Hurley's externalism about perception. Causes of sensory input need to be inferred as they are to some extent hidden.

I found the picture sketched by Hohwy in this chapter both clear and attractive. I would be interested in examples where problems of agency (such as disruptions in the capacity to choose one option over another or in the capacity to act consistently) could be explained as problems of "perceptual disunity". If the transition from perceptual to active inference were somehow compromised and, say, two hypotheses were seen as prediction error minimisers, maybe not simultaneously but in very close temporal succession, then would paralysis of action or inconsistent action patterns result? Could this maybe explain phenomena such as "double-bookkeeping" in delusions?

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 9

Chloë FitzGerald

Welcome to the Philosophy of Mind and Psychology Reading Group hosted by the Philosophy@Birmingham blog.

This month, Chloë FitzGerald introduces chapter 9 of Jakob Hohwy's The Predictive Mind (OUP, 2013). Chloë is postdoctoral Fellow on the project Understanding Implicit Bias in Clinical Care at iEH2 (institut Ethique Histoire Humanités), Centre Médical Universitaire, Université de Genève.


Chapter 9 - Precision, Attention and Consciousness
Presented by Chloë FitzGerald

In Chapter 9, Hohwy describes how the PEM framework can be used to explain the functional role of attention and to illuminate the relation of attention to conscious perception. He claims that the PEM theory of attention is the best explanation we currently have of attention.

Hohwy’s account follows Karl Friston and colleagues’ proposal that ‘attention is just optimization of precisions in hierarchical prediction error minimization’ (p. 194). The sensory signals received by the brain vary in how reliable they are and this variability needs to be gauged to enable perceptual inferences to work well. This is why expected precisions are important for PEM. Howry explains that the brain needs to select where to put in most effort in prediction error minimization and that this effort should be spent where the prediction error signals are expected to be most precise. Attention thus ‘requires learning state-dependent patterns of noise and precision and then using such prior beliefs to set the gain on prediction error’ (p. 195).

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 7

Kengo Miyazono

Welcome to the Philosophy of Mind and Psychology Reading Group hosted by the Philosophy@Birmingham blog. This month, Kengo Miyazono, post-doctoral research fellow at the University of Birmingham, introduces chapter 7 of Jakob Hohwy's The Predictive Mind (OUP, 2013).


Chapter 7 - Precarious Prediction
Presented by Kengo Miyazono

In chapter seven, Hohwy describes the ways in which perceptual inference is tuned in order to represent the world correctly and the ways in which it goes wrong.

The chapter discusses many different issues, but the central idea is that maintaining the "balance between trusting the sensory input and consequently keeping on sampling the world, versus distrusting the sensory input and instead relying more on one's prior beliefs" (146) is crucial in the successful operation of perceptual inference. Maintaining it is not a trivial task. And, the failure of the maintenance might be responsible for pathological conditions such as delusions or autism.

In principle, the prediction errors that are expected to be precise are allowed to drive revisions of prior beliefs higher up the hierarchy, while the prediction errors that are expected to be imprecise are not allowed to do so. Ideally, we expect high precision in predictions errors and, hence, allow them to drive belief revisions when they are trustworthy and expect low precision in prediction errors and, hence, do not allow them to drive belief revisions when they are not.

But, the process can go wrong. A possibility is that some people expect sensory prediction errors to be much less precise than they actually are. Hohwy suggests that this is what is happening in people with delusions; "a persistent, exaggerated expectation for noise and uncertainty would lead to imprecise sensory prediction errors mediated by low gain on sensory input and heightened reliance on top-down priors. 

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 6

Rachel Gunn

Welcome to the sixth post of the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. This month, Rachel Gunn, PhD student at the University of Birmingham, presents chapter 6 of The Predictive Mind by Jakob Hohwy (OUP 2013).


Chapter 6 - Is predicting seeing?
Presented by Rachel Gunn

In Chapter 6 Hohwy asks the reader “does what we believe to some degree determine what we perceive?” (p.118). My initial reaction to this is – yes, of course it does. I believe that many perceptual experiences are cognitively penetrable. It seems straightforward that different people often see different things depending on prior beliefs. A person who believes in ghosts will see their dead mother in the reflection on a darkened window whereas the person who does not believe in ghosts will just see a weird reflection. This may be a similar finding to Hohwy’s reference to people who believe in extra sensory perception seeing more meaningful patterns than others in ‘noisy’ images (p.134).


The other day, looking at an object in the half-light I saw a small bottle or jar that looked like a tiny paint pot or maybe a pill bottle – this experience lasted for 2 or 3 seconds. At a self-conscious level I couldn’t understand what it was or why it was there, once that self-conscious (person-level) knowledge was realised “there is no paint pot/pill bottle like that in this house…” it suddenly looked like what it actually is – a connector for a garden hose. My perception – that it was a pill bottle/paint pot was altered when I applied the new knowledge – it no longer looked like a pill bottle. I wonder if this would this have worked if the knowledge had been supplied by another person – for example, if I’d seen this at someone else’s house I wouldn’t have had the knowledge “there is no paint pot/pill bottle like that in this house…” If someone said to me “…it’s definitely not a pill bottle” would that have been the right kind of additional person-level information to alter the perception? I have a strong intuition that ‘subjective’ information often comes with a higher probability than information supplied by a third party (and this might be important in cases of delusion). I’m not sure how this impacts on PEM or the notion of the Bayesian brain except perhaps to highlight that subjective probabilities are complex and perhaps impossible to grasp except in terms of, in this case, perceptual outcomes.

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 5

Jona Vance

Welcome to the fifth post of the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. This month, Jona Vance (Northern Arizona University) presents chapter 5 of The Predictive Mind by Jakob Hohwy (OUP 2013).

Chapter 5 - Binding is Inference
Presented by Jona Vance

Part 1 of the book (Chs 1-4) sets out the prediction error minimization (PEM) framework. Part 2 (Chs 5-8) applies the PEM framework to a number of specific problems and phenomena in cognitive science and the philosophy of mind. This post is on Ch 5, which addresses the binding problem (or problems). 

Hohwy has two main stated aims in Ch 5. First, he aims to use PEM to give a “reasonably detailed answer” to the binding problem. Second, he aims to use the debate about binding issues and the phenomena it centers on to illustrate how the PEM framework can be applied to various interesting cases. So the chapter aims to use PEM to illuminate how binding works and aims to use binding to illuminate how PEM works.

Hohwy glosses the binding problem in a few ways. On one gloss it concerns “how the brain manages to discern properties of objects in the world and correctly bind these properties together in perception” (p. 101). A second gloss adds that part of the problem is to explain how the brain correctly binds properties “in spite of processing them in different regions throughout the brain” (p. 101). For example, if visual receptors receive information as of something red and as of something round and the olfactory receives information as of something sweet, the brain still has to figure out whether the redness, roundness, and sweetness are properties of the same object or not. And it has to do so despite processing some of the information in different regions.

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 4

Zoe Jenkin

Welcome to the fourth post of the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. This month, Zoe Jenkin (Harvard) presents chapter 4 of The Predictive Mind by Jakob Hohwy (OUP 2013).


Chapter 4 - Action and Expected Experience
Presented by Zoe Jenkin

The first three chapters of The Predictive Mind sketch how prediction error minimization underlies all perceptual processing, explaining various features of the mind using one unified framework. Chapter four addresses the question of how action fits into the PEM framework, arguing not only that PEM can adequately accommodate action, but also that action plays a crucial role in minimizing prediction error. We end up with a picture on which in any given case of a prediction error (a discrepancy between the prediction of the system and the sensory input), this error can in principle be minimized in one of two ways—by revising one’s priors and generating a new hypothesis, or by acting so as to selectively sample the world in a way that makes the input data match the selected hypothesis. An example of such selective sampling might be, if the system predicts that there will be a face before it, it will fixate its eyes toward the region where the prediction dictates a nose will be, and scan for a surface with a characteristically nose-like slope. Hohwy notes that this active, selective sampling method will be more efficient than random sampling, because it will target regions of space where the hypothesis makes a particular or unique prediction and so can easily be confirmed or disconfirmed. On this view, “perceiving and acting are but two different ways of doing the same thing” (71), where that “thing” is minimizing prediction error.

Philosophy of Mind and Psychology Reading Group -- Hohwy Replies to Siegel

I am posting this on behalf of Jakob Hohwy, author the book we are currently discussing, The Predictive Mind (OUP 2013). It is a reply to Susanna Siegel's post on chapter 3.

Jakob Hohwy

Thanks to Susanna for this set of really nice, and challenging, questions. I’ll try to address them here. I do hope others might have insights to share on some of these issues!

First question: What are proper grounds for low confidence in a signal?

The signal can buck the trend in different ways. Importantly, a signal can change such that even if it has the same mean, it loses precision (e.g., a sound becomes blurry). This bucks a precision trend. This is sufficient for decreasing the trust in the signal. This is a reasonable response (and is seen in the ventriloquist effect). We build up expectations that deal with such state-dependent changes in uncertainty. Sometimes we will appeal to higher-level, slower regularities that interact with the low level expectations in question (my headphones are running out of battery, that’s why the sound has become blurry). This will often help in a particular case, but might not (I might rather learn I have developed otosclerosis, or I might need to adjust to new levels of irreducible noise). But if I do rely on the battery hypothesis then I down-grade the trust in the current signal. A similar story can be told for a change in mean, as when the location of the sound-source seems to change. Here I might appeal to an expectation about interfering causes that push the sound-source around. But if I assume the sound shifts due to some kind of echo chamber, then I’d be justified in trusting the signal less. The underlying story here is that the brain in the long run will end up apportioning noise to the right sources, and thus being able to make the right decision about any given signal.

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 3

Susanna Siegel

Welcome to the third post of the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. This month, Professor Susanna Siegel (Harvard and Birmingham) presents chapter 3 of The Predictive Mind by Jakob Hohwy (OUP 2013).

Update: on 4th May we posted a reply to this post from Jakob Hohwy that can be seen here.

Chapter 3 - Prediction Error, Context, and Precision
Presented by Susanna Siegel

Chapters 1 and 2 sketch a picture on which the brain generates perceptual experiences and judgment by relying on learned expectations to help interpret sensory signals. The need for interpretation arises initially because the signals are informationally impoverished, compared to the contents of the perceptual experiences and judgments that we end up with. The main point of Chapter 3 is that in addition filling in missing about the external world that’s missing from the initial sensory signal, there is a second dimension along which the brain has to respond to the sensory signal. It has to assess whether any given signal itself is ‘noisy’, where this means that it is not the result of a mechanism that systematically relates the subject to the distal stimulus that the perceptual experience purports to characterize. A signal is noise if it results from a random fluctuation, or some other process that isn’t systematically connected to any properties or objects in the world.

There are thus two sources of uncertainty that each generate a need to interpret sensory signals: The first-order impoverishment of the initial sensory signals themselves, and the second-order uncertainty about whether to ‘trust’ whatever information is given by the sensory signals, however paltry that information may be.  

Hohwy describes what’s needed to address the problem of second-order uncertainty in several ways. What’s needed is “second-order perceptual inference”, “engaging in second-order statistics that optimize precision expectations”, a “need to not only assess the central tendency of the distributions, such as the mean, but the variation about the mean”, a need to “modulate the way prediction errors are processed in the perceptual hierarchy”. Suppose I’m collecting signals and they form a trend. Now the n^th signal comes in. The trend predicts that the n^th signal will say “Yellow”. But instead the signal says “Grey”. Suppose I have little confidence in this signal. My second-order verdict on whether to trust it is that it’s probably unreliable.

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 2

Welcome to the second post of the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. This month, Alastair Wilson (Birmingham Fellow in Philosophy specialising in Metaphysics and Philosophy of Physics) presents chapter 2 of The Predictive Mind by Jakob Hohwy (OUP 2013).

Alastair Wilson

Chapter 2 - Prediction Error Minimization
Presented by Alastair Wilson

According to the perceptual error minimization (PEM) model, perception is inferential. Chapter 2 addresses a crucial question for any inferential approach - where do the priors come from? - and argues that PEM offers a new answer to this question.

A statistical illustration Translating talk of Bayesian priors into curve-fitting for illustrative purposes, what we want is a mechanism which will optimize the trade-off between accuracy and over-fitting. This means that there is a need to factor in expected noise levels in the incoming data when determining how low to force the prediction error. PEM implements this via the following feedback loop:

Use prior beliefs harnessed to an internal model to generate predictions of the sensory input	→	Revise models prediction or change sensory input to minimize prediction error subject to expectations of noise.
	←

Reconceiving the Relation to the World  PEM goes beyond the analogy with trial-and-error procedures. The primary representational content of perception is encoded in the downwards/backwards connections between levels in the hierarchy rather than in the upwards/forwards connections. That is, perceptual content primarily consists in the predictions that higher levels are making about lower levels rather than in any top-down interpretation of the signals that higher levels receive from lower levels. "The functional role of the bottom-up signal from the world is then to be feedback on the internal models of the world." (47)

Philosophy of Mind and Psychology Reading Group -- The Predictive Mind chapter 1

The Predictive Mind
by Jakob Hohwy

Welcome to the online reading group in the Philosophy of Mind and Psychology hosted by the Philosophy@Birmingham blog. Our first book is Jakob Hohwy’s The Predictive Mind (OUP, 2013). We have a new post on the last Friday of each month. Who is “we”? Many of the people involved are affiliated with the Philosophy Department at the University of Birmingham, but everyone is welcome to participate. To present a chapter by writing a 500-word post on it, please contact Lisa Bortolotti. Comments will be moderated and so there may be a delay between submitting them and seeing them published on the blog.

Chapter 1 – Perception as Causal Inference
Presented by Lisa Bortolotti

In the book, Jakob Hohwy presents and defends the theory that “the brain is a sophisticated hypothesis-testing mechanism, which is constantly involved in minimizing the error of its predictions of the sensory input it receives from the world.” According to Hohwy, the theory is supported by philosophical argument and empirical evidence. Its greatest appeal is its unifying power. The basic idea is that the mind “arises in, and is shaped by, prediction.”