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.

The Theory of Affordances (Gibson, 1979, Chapter 8)

The most influential part of this book is the theory of affordances. We still argue a lot about what these are and how they work, because they are slightly weird (at least from the traditional point of view). So it was interesting to go back and read Gibson's original approach. I was struck by how much sense it makes in the context of the previous chapters; the book really builds and develops and this chapter should be discussed in that context I think.

Environments are the surfaces that separate substances from the medium. But these configurations of surfaces aren't simply there; they offer possibilities for action. They afford things to the animal. Gibson asks 

How do we go from surfaces to affordances? And if there is information in light for the perception of surfaces, is there information for the perception of what they afford? Perhaps the composition and layout of surfaces constitute what they afford. If so, to perceive them is to perceive what they afford. This is a radical hypothesis...

pg 119

In this chapter, Gibson does not offer a single straight-forward definition; that's not really how this works. Instead he lays out examples, and uses those to constrain the concept. As usual, ecological categories have fuzzy boundaries and this is ok!

The Optical Information for Self-Perception (Gibson, 1979, Chapter 7)

So far we have considered what the world looks like to a point of observation that may or may not be occupied. It was important to Gibson that he establish that the optic array available at such a point is public, not private, and so can be shared across individuals (see Chapter 1 for the problem and 3 for the solution). In this chapter, Gibson asks what is seen by an individual when they occupy a point of observation, and in this case there is some privately available information that specifies things about the self. 

Events and the Information for Perceiving Events (Gibson, 1979, Chapter 6)

In the previous chapter, Gibson introduced the notion of the ambient optic array and discussed the kinds of information it can have (flow, and invariants). The focus there was what is revealed by a moving observer. This chapter is about what is revealed as the environment changes; when events occur. 

Sabrina blogged this chapter here and here.