Wednesday 3 November 2021

Is Direct Perception Plausible? Ecological Information

We're in the home stretch of working through how direct perception is, at least, an option, and how the ecological approach in particular attempts to make it work. We've talked about what direct vs indirect means, the kinds of properties direct perception needs to be out there in order to work, and affordances/effectivities-as-dispositions as the specific properties ecological psychology claims are out there and fit the bill

I ended that last post by highlighting ecological psychology had one last thing to do in order to be plausible, and that is to have a way to bring affordances and effectivities together into a kind of contact that allows them to work together. That contact can't be mechanical, or simply physical proximity, because almost all of the things we perceive and act with respect to are not in that kind of contact. The ecological solution is informational contact, and so this post will build on the pieces I've assembled to identify what kind of thing ecological information has to be in order to work. 

The Objects of Perception

This phrase refers to the question of what it is about the world that perceptual systems are initially, preferentially tuned into. Ecologically, the objects of perception are possibilities called dispositions, specifically the possibilities for action we call affordances (dispositions of the environment) and effectivities (dispositions of the organism). 

We established last time that dispositions are higher order properties that are formed by how simpler material properties are arranged in space with respect to one another. Two posts ago, we established that higher order properties are allowed to be the kinds of things that are measured directly, if the measurement device is of the right kind; recall the example of the polar planimeter. Higher order properties are legitimate potential objects of perception, so that's all good. 

Information for the Objects of Perception

Indirect theories of perception get to these kinds of higher order properties by detecting the lower order pieces and somehow implementing the operation required to place them into the correct relation. This is what it means when indirect theories talk about constructing a mental model of the world. 

Direct theories aren't allowed to do this, so we need there to be information variables available to perceptual systems that are already about our higher order affordance/effectivity properties. Gibson pointed this out when he said
The central question for the theory of affordances is not whether they exist and are real but whether information is available in ambient light for perceiving them.
Gibson, 1979, pg 132
We have some constraints to work within. In order for there to be information about a higher-order property like an affordance/effectivity, that information itself has to be a higher-order variable that can be measured in and of itself. We can point to the polar planimeter again to say that this isn't an immediate dead-end. 

That information variable also has to be about the affordance/effectivity property; this is harder.

Is Information a Copy of an Affordance Property?

One option could be that the information is a copy of the affordance/effectivity property, just implemented in a perceptual media rather than an object. That would make it trivially "about" the affordance/effectivity, and detecting information that was a copy of an affordance would bring that copy into physical proximity to the effectivities. As a general rule, this idea is generally considered unworkable (Turvey, 2019, Lecture 4 gets into it), and would also mean perception was not directly of affordances; the object of perception would be an information variable. In the particular case of ecological psychology, this copy hypothesis really fails because of how information is created and a key limitation of the media information is created in. Bingham (1988) analysed this idea as the 'perceptual bottleneck'.

Affordances and effectivities are properties of the physical environment. At the ecological scale, a complete description of a physical property requires a dynamical description; specifically, one that uses units of time, position, the temporal derivatives of position like velocity, and mass. We need these units to characterise where objects are and how they respond to forces trying to change that state. However, we can generate complete descriptions of informational media such as the optic array with only kinematic descriptions; time, position, the derivatives, but no mass. This is because at the ecological scale, these media are relatively low-energy; they don't cause things to change state via the transmission of forces. You don't try to catch a ball because the light pushed your hand. 

Kinematic information can therefore not be a copy of a dynamical property, because it is missing a dimension. We need another way to build information variables in low energy perceptual media such that these higher-order patterns are about the affordance property. 

Affordances Entail Information, Information Entails Affordances

In order for one thing to be about another thing without any additional factors being included, the things must entail one another. An entailment is what we call it when you have a set up that propagates truth. So for example, 'X entails Y' means that the presence of X means Y is also present. If you also have 'Y entails X' then the presence of Y means X is also present. 

The whole package required to these two things to be intrinsically about each other is "X entails Y and Y entails X"; this circular loop is another example of impredicativity, and of the kind of loopiness we need in general in direct perception. The ecological approach needs to be able to say 'affordances X entails information Y, and information Y entails affordance X'; this way, if the affordance is present you get the information, and if you have the information you also effectively have the affordance. 

Entailments aren't mediating states; if you're doing a little 'if X then Y' analysis in your head, you're doing something indirect. In order for affordances to entail information, and for information to entail affordances, they need to be related in a way that implements the entailment. The best way is via a law. 

Affordances & Effectivities Lawfully Create Information

Affordances and effectivities are real physical properties (just weird dispositional ones). Real physical properties are the kind of thing that light can bounce off, or that can create waves in the atmosphere. These low energy perceptual media can bear the consequences of that interaction; one way is how interactions can filter the available frequencies so that an object appears red, for example. The medium (e.g. photons) hits the affordance/effectivity, bounces off, and is been transformed into a structured array. Each affordance/effectivity property structures media differently, but because of the laws of physics, a given affordance property always structures media the same way.

The net result is that when an affordance is present in a perceptual media, it creates one and only one higher order pattern in that media. We call this higher order pattern an information variable. The affordance entails that information variable, and the variable entails the affordance, all because of the law that governs how the one creates the other in a perceptual media. We've established that the information variable cannot be a copy of the affordance property, but because there is a law-guaranteed 1:1 relationship between them (each affordance creates one variable), we can say that the information variable specifies the affordance. 

Connecting the Pieces

Now we have everything we need. There are higher-order behaviourally relevant properties in the environment, specifically a subset of dispositions we call affordances. There are also higher-order environmentally relevant properties in the organism, specifically a subset of dispositions we call effectivities. These come in complementary pairs; an affordance implies an effectivity, and vice versa (they don't entail each other though; not every affordance can be currently effected, which is why the Olympics is still exciting). 

These dispositional properties are dynamical properties. They can interact with a variety of low-energy perceptual media (light, the atmosphere, etc). When they do, that interaction is governed by ecological scale laws of physics that mean, for example, that a given affordance will produce one and only one pattern in the media, and it will always produce that pattern. The laws underpin an impredicative entailment; the affordance entails the information, and the information entails the affordance. 

If an organism's perceptual system reacts to such an information variable (and not the parts), then this connects an affordance disposition to an effectivity disposition and that disposition can become an actuality; a behaviour. 


Direct perception is plausible. Suitably weird physical properties are legitimate options at a variety of physical scales, up to dispositions at the ecological scale. These properties can interact with the low-energy perceptual media that organisms and their environments are embedded in, and the way they interact is governed by laws of physics. These laws mean that a given affordance property will always produce one and only one pattern in that media; that pattern is not identical to the affordance but the 1:1 mapping means that it does specify the affordance. Detect that information, and you perceive the affordance, no additional mediating steps required. Perception can be direct.

So it's possible. But we've had to a do a ton of work to get here, in which we've gone hunting for weirder physical properties and had to learn a bunch of intimidating words. This is all ok; there was no reason understanding perception had to be easy. It does mean I've run the risk of not closing all the gaps in the story here, just because I might have missed something. Let me know if you spot any. But to emphasise, direct perception is not just a tweak on indirect perception - it is different, root and branch. 

To finish, let me paraphrase the Gibson quote from above: "The central question for the ecological theory of direct perception is not whether it's technically possible but whether affordances and information are actually being used to implement direct perception". At this point, allow me to introduce you to 40+ years of research and encourage you to dive in! That said, I do have one more post in mind for this series; fronting up to the challenges of trying to do science on a theory of direct perception and how the ecological approach varies quite a lot in how well we are managing. This shit is, it turns out, really bloody hard. 

But that's ok too. That just makes it fun - it would be a bummer if Gibson had figured it all out by 1979 :)


  1. I tried to write a comment in here but it ended up being too long, so I expanded it into a blog post:

    The thrust of the argument: Yes, I agree that the direct perception model is useful. In fact, I prefer it to the alternatives, but we still need an account of rich mental representations to account for much of our experience of the world in its social and mental context. I give some specific examples, I'd like to have a more plausible account for from ecological psychology.

  2. "When they do, that interaction is governed by ecological scale laws of physics that mean, for example, that a given affordance will produce one and only one pattern in the media, and it will always produce that pattern."

    In engineering terms, the senses are transducers. They convert one form of energy into another. A microphone transduces mechanical energy (i.e. sound waves) into electromagnetic energy. The ear drum transduces sound waves into bioelectric energy. The ear is not "metaphorically" like a microphone - it is an analog of a microphone - or the other way around - the microphone is an analog of an ear. This holds true across all sense modalities.

    I think this is a good way of grounding the "law" you mention above.