Tuesday 26 October 2021

What Does it Mean for Perception to be 'Direct' vs 'Indirect'?

The ecological approach is a theory of direct perception. Put simply, direct perception proposes that our perceptual experience of the world is not mediated by anything that sits between the world and that experience. Making this viable is a big challenge, however, and the idea seems preposterous on the face of it to many people. 

In this post, I want to lay out the basic idea of direct vs indirect perception, and then explain how each approach addresses the problem of how we perceive the world. There will be some big words, but I will aim here to place them in a context that supports them usefully, and focus mainly on the straight-forward ideas in play. In a future post, I will ask the question 'what do we know about how plausible direct and indirect theories of perception are?'

Perceptual Experience

All theories of perception begin with the fact that we experience a rich, detailed world full of things we can and can't do, should and shouldn't do. Specifically, we experience a behaviourally relevant world. It's important that this experience is functional with respect to the real demands of the world; that if we act on the basis of our experience, it works and doesn't lead to us dying horribly. How might this be possible?

There are two basic options. First, perceptual experience might be the result of a two-term relation, with 'us' and 'the world' being the two terms. This would make perception direct. Second, perceptual experience might be the result of an at-least-three term relation, with 'us', 'the world', and 'at least one other thing' being the terms. This would make perception indirect

Indirect Theories of Perception

Indirect theories begin with the assumption that the world does not present itself to us in behaviourally relevant terms, and that we therefore need at least one mediating layer between us and the world in order to transform the way the world presents itself into the way we experience the world. These are broadly motivated and justified by certain theories of physics (i.e. theories of the physical structure of the world). In these theories, objects can have properties that we can assign to them (predicate to them) without any reference to anything else; these are primary, objective properties such as the mass of an object. They can also have properties that cannot be assigned just to them, and require something else in the definition; these are secondary, subjective properties such as the colour of an object. The objective world only contains primary properties. The problem for cognition is that primary properties are not behaviourally relevant properties; mass by itself does not define whether you can move something. Move-ability is, under this analysis, a secondary property.  so we need an intervening process to get to these behaviourally relevant secondary properties - we must make the world a meaningful place. 

Over the centuries there have been a variety of contenders for what that mediating process is, but in modern theories of perception the mediation is implemented by representations. There are many different theories that vary in their details as they try to propose a representational format that can do this successfully (i.e. in a way that doesn't lead to us dying horribly). But across all of these, the core idea of a representation is that it takes the way the world presents itself to us, and processes that information into a re-presentation of the world in behaviourally relevant terms. We then behave as a function of the re-presentation. This feature of representations is called designation (Newell, 1980)

Designation: An entity X designates an entity Y relative to a process P, if, when P takes X as input, its behavior depends on Y

Recent formalisations of designation in the context of cognition can be seen in interface theory (e.g. Hoffman, Singh & Prakesh, 2015) and theories of predictive processing (e.g. the free energy principle, Friston & Kiebel, 2009). These propose ways in which representations can be built by a cognitive system in a way that preserves designation, and explore the consequences for perceptual experience of these construction methods. The general consequence is that perceptual experience is not a physically accurate model (because it contains secondary properties) but that this is just the cost of doing business.

Representational theories face two big challenges: explaining how adaptive representations full of useful secondary properties can be built up when the physical world provides no help on what those might be, and then explaining how we know which representation to deploy at any given time, again because the physical world provides no unambiguous help. 

Theories of Direct Perception

Direct theories of perception instead begin with the assumption that the world does present itself in behaviourally relevant terms, and so we do not need any mediating layer to invent this for us. Instead, we need a mechanism for successfully engaging with that presentation. 

These theories have to begin with a different theory of of the physical world. If the world only provides primary properties, but the properties we need are secondary, direct perception is an immediate non-starter. Some people argue that the physics of primary and secondary qualities is what physics has given us to work with, and if that's the case then perception must be indirect. The main move is to reject the (17th century physics) analysis of the world into primary and secondary properties, and embrace the more recent (21st century physics) claims of theories of physics that there are instead perfectly real properties that cannot be predicated so simply. These properties of things depends on how you ask it; how you measure it. Such properties are referred to as impredicative, and historically they have been frowned upon because their existence seems to require a circular definition. However, modern physics has spent 100 years showing that impredicative physical properties are not just legitimate options but also everywhere - quantum physics is a terrifyingly successful theory of impredicative properties. The ecological approach must therefore rely on a theory of impredicative physical properties at the ecological scale. We can point to the success of quantum physics to show this isn't an immediately doomed approach, although we cannot rely on the same set of impredicative physical properties as quantum physics; we have to find them ourselves.

Ecological theories face two big challenges: identifying the physical basis that would allow the world to present itself in behaviourally relevant terms, and identifying the mechanism that supports engaging with that presentation. Our solution to the first challenge is affordances, and our solution to the second is specifying ecological information. As Gibson famously noted, identifying affordances is easy - they are definitely there. The real challenge is whether these are what we perceive - are these what information is about? (This is also the essence of the famous Fodor & Pylyshyn (1981) challenge to the ecological approach.)


This post lays out the basic problem facing all theories of perception, and the two basic solutions that have been proposed. In the next post, I will discuss how plausible these two solutions are. I want to note at this point that the plausibility question is generally only levelled at direct perception; most people find indirect perception to make more intuitive sense. But it's an important question to level at indirect perception as well, because when we do we find serious reasons to doubt that it's plausible at all. 


  1. This was incredibly clear, so thanks! If you have any tips on how to formulate a theory of embodied imaginING that is built up from the reenactment of remembered acts of direct perception, I'd be much obliged!

  2. As you are using the terms, I would say that animals have direct perception (non-representational) and humans (as far as we know) are the only animal capable of indirect observation i.e. forming representations.

    The idea of Representations arises due to our unique ability to "observe" that "we" are "observing" our "observations" of the "things" that we are "observing".

    Our observations (representations) become "things" every bit as much as the, proverbial, thing in itself. And so does our representation of ourselves.

    I wouldn't read to much into Locke's (and Newtons) idea of Primary and Secondary characteristics. Neither had quite yet let go of the metaphysics of St. Thomas which was influenced by Plato and Aristotle. Form (i.e. extension) was still rather hazy in their minds and was tied into the inherent geometry of kinematics. And I wouldn't draw to heavily from QM. QM is actually "classical mechanics".