Not Every Behaviour Entails an Affordance

There are two approaches to formalising Gibson's notion of affordances. The first is to treat them as dispositional properties of the environment; properties the environment offers the organism to support possible actions. The second is as relations in the organism-environment system; not localised to the environment but formed when the organism-environment system is formed as a perception-action loop. I am firmly Team Dispositional Properties, because I think this best aligns with Gibson's goals, it allows actual science on the coordination and control of action (Wilson, 2026) and because there is currently no working account of how you might perceive a relational affordance. 

Despite all this, the relational account remains alive, well, and probably the main way people think about affordances. One reason is the drive to make ecological psychology align with the commitments of radical enactivism, a drive I have no interest in (I think enactivism is ok but nothing we owe our allegiance). I think the other big reason is that only the relational account really allows you to talk about affordances for things other than the coordination and control of actions, and as the ecological approach expands the things it is trying to explain people want to apply the ecological tools we have, and that means affordances. 

Except actually, it doesn't. 

Locomotion and Manipulation (Gibson, 1979, Chapter 13)

Gibson turns his attention now to two major forms of behaviour, locomotion and manipulation, and discusses the optical basis for the control of these action. He considers the visual information available in these tasks, and how these can be used to control the behaviours, without appeal to a central controller (such as the brain). In this chapter Gibson proposes that these and other behaviour are all 'regular without being regulated' (pg. 215) and the question is, 'how can this be'? While he doesn't fully answer this question, he introduces the key optic flow features we will need for these two behaviours. 

Looking with the Head and Eyes (Gibson, 1979, Chapter 12)

In this chapter, Gibson places head and eye movements on an ecological footing, and makes them the activity of a distributed perceptual system (c.f. Gibson, 1966) who's job it is to look around. 

We have to look around because our heads get in the way of our eyes. Even animals with eyes on the side have this problem, but for animals with front-facing eyes over half the optic array that is ambient to a point of observation is occluded by the head (which of course also specifies the presence of the self). Looking around is about reversing that occlusion and revealing things as required. 

The Discovery of the Occluding Edge and Its Implications for Perception (Gibson, 1979, Chapter 11)

Gibson introduced us to the notion of occlusion in Chapter 5. Occlusion is when one surface is progressively covered up by another surface, and the details of how optical texture is deleted specifies the occluding edge and the fact that occlusion is happening. In this chapter, Gibson details the radical implications of this fact of the optic array for theories of perception. Most importantly, given occlusion, vision cannot be based on images, series of images, or perspective structure, and it is not limited to working when sensations fall on the retina. Vision is a process that extends back and forwards in time, and this is enabled by information. 

Experiments on the Perception of Motion in the World and Movement of the Self (Gibson, 1979, Chapter 10)

Chapter 9 was about perceiving persistence in the environment. Chapter 10 is about perceiving change, and the evidence that this also might be direct. 

In contrast to retinal image based theories, Gibson proposes that change is perceived because of 'disturbances of structure in the ambient array' (pg 162). A key point here is that 'Disturbances of structure can specify events without being similar to them' (pg 162); this is a key fact about information. It does not get its meaning because it is somehow a copy of the world; it gets its meaning because of the laws that govern it's creation. 

Some Thoughts on 'The Simons Collaboration on Ecological Neuroscience' (SCENE)

Last year the Simons Foundation announced a massive multi-centre grant project called SCENE: The Simons Collaboration on Ecological Neuroscience. At the time, those of us interested in ecological neuroscience were surprised that this existed, because none of us were involved. We noted that the core approach seemed off: "Inspired by ecological psychology, SCENE proposes that one of the brain’s core functions is to encode affordances..." isn't actually what an ecological neuroscience would ever be about. 

Just this week, the consortium published a piece in Neuron detailing the project and it's goals, and this just confirms their actually non-ecological take on an ecological neuroscience:

SCENE focuses on the task structures that animals evolved to solve rather than the detailed input statistics upon which they operate.

and

In SCENE, we consider a task to be ecological if it includes three elements: (1) a closed perception-action loop, (2) sequences of actions and a delayed reward structure that creates a credit-assignment problem in linking actions to outcomes, and (3) partial observability, requiring brain states that synthesize sensory inputs over time to infer hidden world variables and guide actions. This last element, partial observability, marks a key departure from traditional ecological psychology and its notion of direct perception. We do not espouse Gibson’s claim that all information needed for action is directly accessible in sensory inputs, nor do we share his aversion to the concept of a representation....our use of the term ‘‘ecological neuroscience’’ draws inspiration from ecological psychology, with its emphasis on perception-action loops and environmental affordances, but extends it toward mechanistic neurobiological and computational accounts that can span species and neural systems

In other words, they are applying a theory of indirect perception and will not be studying how the brain interacts with information. 

My question is this: why call this ecological neuroscience?

Experimental Evidence for Direct Perception: Persisting Layout (Gibson, 1979, Chapter 9)

We've now completed the first two sections of the book, which lay out the ecological approach. Gibson now turns to a review of the (at the time) existing empirical evidence for the various claims he has made. The first chapter focuses on how information supports the perception of a persisting layout of surfaces.