Medium, Substances, Surfaces (Gibson, 1979, Chapter 2)

In this chapter, Gibson continues to lay out the rules of the environment (vs the physical world). In physics, there are objects in spaces, but this simply does not work as the basis of perception (see the chapters about Helmholtz and the limits of unconscious inference in the Turvey book). Instead, environments are made of medium, substances, and surfaces, and this chapter defines these at the ecological scale.

This chapter introduces a lot of vocabulary for talking about the environment: I have reviewed some of it, but see the chapter for the full set because it is going to be needed as we described the environment to be perceived. 

Note: Sabrina also blogged this chapter here.

The Animal and the Environment (Gibson, 1979, Chapter 1)

Gibson's first chapter introduces his notion of the environment. This is a distinct level of description from the world according to physics, even though everything in it is still made of physical stuff. The environment is the ecologically-scaled surroundings to an organism, and Gibson lays out some of the key differences between this and the physical world here. Why? Because perceiving is going to be of the environment, and not of the physical world, and as we progress this is what the word 'environment' will mean.

Note: Sabrina also blogged this chapter here.

Introductions in the 2014 Edition (Gibson, 1979 Reading Group)

The 2014 reprint of Gibson (1979) includes the original Preface and Introduction, as well as an Introduction to the Classic Edition by William H Mace. A few things come up in Gibson's sections that I thought were cool, and worth documenting as part of the reading group. 

Mace's Introduction does some nice work reviewing Gibson's intellectual development over the course of his career and exemplified by his three books. He points to how the ecological approach has grown and connected to other fields in the years since Gibson's death, and talks about how the 1979 book was received (a mixed bag, to say the least!). It's a good read, but it doesn't have much new content in it so for this reading group I'll just focus on the bits Gibson says that set things up nicely. 

Reading Group - Gibson (1979) The Ecological Approach to Visual Perception

Rob, Marianne, and I had so much fun with the Turvey (2019) reading group that we decided to keep going, and we decided to return to the source - Gibson's 1979 book. Buckle up, this should be fun!

We'll be using the 2014 edition, so all page numbers will refer to that (I have the feeling I will be directly quoting the eminently quotable Gibson a lot more than I did with Turvey!). I will use this page to link to my post, and the video and podcast links for our group discussions, for each chapter.

Gibson (1979) The Ecological Approach to Visual Perception

Introductions in the 2014 edition

Part I: The Environment to be Perceived

Chapter 1: The Animal and the Environment  

    Blog || Video || Podcast

Chapter 2: Medium, Substances, Surfaces  

    Blog || Video || Podcast

Chapter 3: The Meaningful Environment  

    Blog || Video || Podcast

Part II: The Information for Visual Perception

Chapter 4: The Relationship Between Stimulation and Stimulus Information  

    Blog || Video || Podcast

Chapter 5: The Ambient Optic Array  

    Blog || Video || Podcast

Chapter 6: Events and the Information for Perceiving Events  

    Blog || Video || Podcast

Chapter 7: The Optical Information for Self-Perception  

    Blog || Video || Podcast

Chapter 8: The Theory of Affordances  

    Blog || Video || Podcast

Part III: Visual Perception

Chapter 9: Experimental Evidence for Direct Perception: Persisting Layout  

    Blog || Video || Podcast

Chapter 10: Experiments on the Perception of Motion in the World and Movement of the Self  

    Blog || Video || Podcast

Chapter 11: The Discovery of the Occluding Edge and Its Implications for Perception  

    Blog || Video || Podcast

Chapter 12: Looking with the Head and Eyes  

    Blog || Video || Podcast

Chapter 13: Locomotion and Manipulation  

    Blog || Video || Podcast

Chapter 14: The Theory of Information Pickup and Its Consequences  

    Blog || Video || Podcast

Part IV: Depiction

Chapter 15: Pictures and Visual Awareness  

    Blog || Video || Podcast

Chapter 16: Motion Pictures and Visual Awareness  

    Blog || Video || Podcast

Lecture 26: Strong Anticipation and Direct Perception (Turvey, 2019, Lectures on Perception)

In this final chapter, Turvey lays out the basics of the ecological approach to coordinating action with respect to the future. This is actually a key part of behaviour - we reach for things we know are graspable before grasping them, we move to intercept or avoid things before they are anywhere near us, and so on. The question is how do we do this.

The ecological approach cannot, of course, use prediction to solve this problem. Prediction entails representation, making educated guesses about what is coming up based on loans of intelligence we cannot ever pay off. The whole point of this book has been to lay out the argument that a) this approach is doomed to fail but that b) the ecological approach, grounded in laws, is different enough in kind to be a viable option. 

Coordinating with things not in the immediate present is therefore going to rely on lawful informational coupling to dynamical events, with several interesting consequences. 

Lecture 25: The Mechanical Basis for "Getting About Among Things" (Turvey, 2019, Lectures on Perception)

This chapter is about the mechanical consequences of interacting with the environment; what happens when we come into physical contact with things. Importantly, though, we are going to focus on the informational consequences - what information is created by mechanical interactions, what does it enable us to perceive, and what is the medium for this information? Broadly then, the topic of this literature is dynamic/effortful touching. 

Talking about this topic will enable us to make a few key points. First, dynamic touch is a commonplace activity, namely the kind of activity an ecological psychology takes as it's main topics. Second, it engages with the ecological hypothesis that information is specific to the dynamics of what it is about, and not specific to the medium in which it lives. Visual information and haptic information, for example, are the same kind of thing, and are sometimes even the same information variable. The important thing for a theory of perception is the information, and not the details of the medium, nor the anatomy that happens to pick it up. 

Turvey then spends most of the chapter reviewing key empirical findings from the ecologically motivated investigation of dynamic touch. The key perceptual variables are not things like mass or weight, for example, but the moments of inertia; how an object resists changing state. This leads to tasks that involve hefting or wielding (changing the state, essentially), and experimental manipulations that separate out things like mass from mass distribution and the inertia tensor. 

Several things emerge. People can perceptually identify different properties via similar movements, by attending to different properties of the object. This demonstrates that intentionality matters (you can ask people to judge different things and that drives attention to different variables), and that in any task there are multiple variables available, defined across various scales and relations between properties (the task is multi-fractal). These mechanical properties are also the basis of perceiving things about ourselves, as well as what objects we are mechanically interacting with; we perceives things about our limbs this way as well as things our limbs are dynamically touching. There's no in-kind difference between perceiving ourselves and other things, it's all grounded in informationL. Finally he notes the case of weight perception, and how it is not based on the weight of objects, but on their inertia (this connects to Gibson's point, that the variables of perception must be empirically discovered and confirmed, not assumed from one description of the task at hand). This connects to things like the size-weight illusion and reveal it's only an illusion given the assumption of the wrong variables at play. 

Turvey then discusses a fascinating case, a man called Ian Waterman who lost all proprioception and had to effortfully replace that perception of the environment with vision. The details of his ability to do so and the limits on what he could do are a fascinating story for ecological psychologists (some clips from a documentary here, and there's a great book about it too). 

Turvey briefly reviews his hypothesis that the medium for all this mechanical interaction perception is the body considered as a tensegrity structure (Turvey & Fonseca, 2014). The hypothesis is that the way the body deforms under mechanical pressure provides a medium for the same kinds of structure as the optic array does; it has the right kind of features to support implementing informationL. Analogous to the optic array, the key is the right level of description - the optic array begins with optical solid angles, for example, rather than points or rays of light. 

Turvey then notes briefly that hearing is also about the detection of mechanical events, just not necessarily ones in which our body was involved. He points to the work of Gaver (1993a, b) on the kinds of events that can be specified in the acoustic array, and how we can 'hear what a struck object looks like' because of the nature of the informationL involved. 

Lecture 24: Perceiving "How to Get About Among Things" (Turvey, 2019, Lectures on Perception)

This chapter focuses on the perception side of the perception-action system we will end up with for behaviour. It covers the objects of perception (affordances), the means of perception (law-based information, informationL), and the notion of prospective control (vs. anticipating or predicting the future). 

The chapter title is 'how to get about among things'. This stands in contrast to how things are normally framed, in terms of distance or space perception. Perception is for action, it is about enabling safe, skilled activity in a cluttered world. Because of this, the objects of perception (what perception is about) must be action related - affordances. For Turvey, affordances are properties of the environment (not relations between environment and organism) and they are perceived if and only if there is informationL about that affordance present and detected. 

Turvey then introduces the idea that perception and action are duals that define a duality (rather than the beginning and end of a linear chain of causation). Note this is a duality, and not a dualism - the two things are not different in kind, but are parts of a greater whole that are intimately and lawfully connected to one another. This implies a relationship between what information specifies, and the energy required to move with respect to what it specifies. The main idea here though is that it is not perception then action, it is only perception-action. 

Turvey then spends time on the optical basis for getting about among things; ecological optics. Ecological optics is not physical optics (which is about things like wavelengths), nor is it physiological optics (which is about the anatomy and physiology of the eye). Ecological optics is about what is available in the light prior to any interaction with an organism, and therefore what is available to stimulate the retina, etc. The key is optic flow: structured light distributions incident to illuminated surfaces. 

The optical structure available at a single point is specific to the stationary surface layout that gave rise to that structure (this is why the Ames Room works, for example). Optic flow is the general case; optical structure in which the transformations are specific to the surface layout and the relative motions of the observer and the environment. Turvey works through the example of tau in some detail, to illustrate how movement generates an optical flow field and how that field is structured specific to the motion. He then briefly reviews more complicated work on other geometrical features of optical arrays (transformations such as divergence, curl, and deformation; Koenderink, 1986). These are examples of the kinds of maths required, and the target of that maths (the structure of the optic array). Turvey also nods to Stoffregan's notion of a global array (although I will note that this hasn't really gone anywhere yet and it's not clear what the medium of this array is). 

Finally, Turvey reviews how optical information can support prospective (future oriented) control. In general there are two approaches to dealing with the future. We have encountered the idea of prediction/anticipation, and the various problems with that. In short, it is a form of induction and it suffers from all the problems of that. Instead, informationL will allow prospective control, via specification of what will occur, if present conditions continue (Bootsma calls this 'the current future'). Turvey of course looks to the outfielder problem as the key example here. 

(I will note here that this topic shows up in the modern literature in the form of information-based control (Bill Warren) vs affordance-based control (Brett Fajen). Turvey nods to Fajen and acknowledges that the information used for control should be about affordances; but the debate is not engaged with here.)

Finally, as a prelude to the next chapter, Turvey notes again the idea that all this information is dual to/reciprocal with the action side of the equation.