Reading Group - Gibson (1979) Chapter 5 Part 2

Chapter 5 Part 2

In this part of Chapter 5, Gibson talks about how various relations between objects can be specified by the ambient optic array. This is important because image-based theories assume that we have to make a lot of inferences to detect, for example, that one object is partially obstructing the view of another object. In contrast, Gibson once again goes looking for regularities in the ambient optic array that can distinguish one relation between objects from another.

Reading Group - Heft (2001) on Gibson (Pt IIa)

Time for a break on affordances, and a quick check in with Heft. In the last chapter Heft laid out the key contributions Gibson made to the radical empiricist programme. In Chapter 4, Heft focuses on the specific consequences for Gibson of being a realist about relations, and continues to tie this to James via Holt. This post will cover the first half of that chapter.

Chapter 3 discussed Gibson's notion of the "mutuality between the knower and the thing known" (p.143). Chapter 4 now turns to "the context within which knowing processes transpire", i.e. the metaphysical landscape that serves as the basis for the act of perceiving. Simply put, this landscape is the rich web of relations between objects and events, which are real and perceivable. This web is the basis for the dynamic stability described by James and required for flexible but reliable behaviour.

Affordances, Part 3: Dispositions or relations - which is it?

Affordances are difficult entities to wrap your head around. We talk about them imprecisely, they seem like odd, ghostly entities that couldn't possibly exist, and even when we get precise about them, we end up with two different accounts of the kind of thing they are.

Gibson did not have a logical framework with which to express what he mean by affordances, although his verbal formulation is quite clear:

An affordance is neither an objective property nor a subjective property; or it is both if you like. An affordance cuts across the dichotomy of subjective-objective and helps us to understand its inadequacy. It is equally a fact of the environment and a fact of behaviour. It is both physical and psychical, yet neither. An affordance points both ways, to the environment and the observer.

(Gibson, 1979, p. 129)

There have been two attempts at formalising this definition, with two incompatible results: for Turvey, an affordance is a dispositional property of the environment, like solubility, which is complemented by an effectivity of an organism. For Stoffregan and Chemero, affordances are relations between the organism and environment. These are not the same and the difference matters: so which is it?

Visual Illusions Again

VSS is the Vision Science's Society conference that's held every year in Naples, FL. I couldn't make it this year, but they have a contest for the best new visual illusion that's usually a pretty good show; illusions are getting cleverer.

This is this year's winner:



There's actually visual information that something is wrong that's available before they rotate the display - 5 internet points to anyone who points it out!

Affordances, Part 2: Affordances are relations between organism and environment

The idea that affordances are dispositional properties of the environment is not immediately obvious, given the way everyone talks about them. This was certainly the source of my confusion - affordances are always described as animal-relative properties of the environment, and in the classic Warren stair-climbing affordance studies Bill Warren pioneered the use of pi numbers to describe affordances. Pi numbers are a handy trick from engineering, where you characterise a relation using a ratio. This has the advantage of a) eliminating the units so you can then rescale the number in any system you like, and b) highlighting that the relation between two things remains common even when the specific details change. Warren found that judgements of climbability varied not with leg length or riser height but with the ratio. Affordances are therefore almost always discussed this way - as being about the relation between an organism and its environment. Ecological psychology eschews internal representation and computation, so this relation must be directly perceived, i.e. they must be affordances.

Affordances, Part 1: Affordances are real dispositions of the environment

It turns out I've been pretty confused about affordances for a long time. This is partly due to the fact that I don't (yet) do research on affordances and so don't spend much time thinking about them. However, it is also partly due to the fact that affordances are fucking weird and much has been written that is confused, incomplete and wrong.

I got back into thinking about affordances in detail by reading Anthony Chemero's mostly excellent new book, Radical Embodied Cognitive Science (Google Books preview). Actually, everything I've written so far is actually me getting my head in the game to go after something I think Tony has gotten needlessly wrong; for various reasons he thinks its time to lower the specification requirement for perceptual information. I think the reasons are flawed and that it's not even close to being an empirical reality that specification is not needed; but this is all material for later on.

When Tony talks about affordances, he proposes that they are relations. He contrasts this to the generally accepted Turvey formulation, that affordances are properties, specifically dispositional properties. This, it turns out, is a key internal battle that is ongoing within ecological psychology. I was initially on Tony's side: Turvey's account has always seemed wrong to me. But after some discussion with my PhD advisor, and after reading Heft's summary of what Gibson meant, I'm back on the side of affordances as properties.

Reading Group - Gibson (1979) Chapter 5

Chapter 5: The ambient optic array

This chapter is long and dense, so I’m going to go through it in two posts. Essentially, Gibson is going to make the case that light can be structured in a way that specifies things about the environment. The important thing to keep in mind is that the structure arises from relations between things ( in this case, relations between solid visual angles). Traditional optics talks about points of light falling on an object. These points of light change all the time and this creates a real mess for any perceptual systems that perceives points of light. Ecological optics talks about the relationship between solid visual angles. Although the particular conditions of light or perspective might change, the nature of these relationships is preserved. To refresh your memory see Chapter 1, 2, 3, and 4. Now, on to details...

Reading Group - Heft (2001) on Gibson

Part II of Heft moves on from James and Holt and into Gibson's ecological approach. The point of Part I, as I've discussed, was to establish the roots of Gibson in the radical empiricism of James, conveyed via the molar behaviourism of Holt. Part II is a detailed discussion of the ecological approach, specifically that laid out in Gibson (1979). I'm therefore going to leave the details of the exposition to the other reading group posts, and focus on the higher level connections and points Heft makes. I'm also going to handle Chapter 3 in two posts: this one will be a brief summary of some key points, and later this week I'll reveal how I've been mistaken about affordances for quite a while.