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.
Showing posts with label Gibson (1979). Show all posts
Showing posts with label Gibson (1979). Show all posts
Monday, 14 September 2026
Tuesday, 7 July 2026
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.
Monday, 15 June 2026
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.
Tuesday, 5 May 2026
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!
Friday, 27 March 2026
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.
Monday, 16 March 2026
The Ambient Optic Array (Gibson, 1979, Chapter 5)
In the previous chapter, Gibson laid the foundations for an ecological optics by distinguishing between stimulation and stimulus information. In this chapter, he lays out the details of how to analyse the source of visual stimulus information, as an ambient optic array that contains both invariant and perspective (variant) structure.
Sabrina blogged this chapter here, here, and here; there is a lot going on in this chapter!
Thursday, 5 March 2026
The Relationship Between Stimulation and Stimulus Information (Gibson, 1979, Chapter 4)
The first three chapters describe the world to be perceived, at the ecological scale. This chapter opens the section on how we visually perceive that world - via information. Remember, a key part of the ecological analysis is doing things in this order (see the Introduction).
The work of the next few chapters is to lay out a theory of ecological optics. Lots of science studies light, but as with the physical world/environment distinction, Gibson will insist on distinguishing between the physics of light and the ecology of it; only the latter will be relevant to a theory of perception.
Sabrina also blogged this chapter here.
The Meaningful Environment (Gibson, 1979, Chapter 3)
In Chapter 1, Gibson identified the animal and it's environment as the two mutually defining parts of an ecological system. In Chapter 2, he developed a vocabulary for describing an environment (as opposed to the physical world). Now, in Chapter 3, he will use that vocabulary to identify that the environment of an animal is meaningful, literally full of meaning, and this will mean that meaning is there to be discovered, rather than constructed (as in every theory of perception so far).
Sabrina also blogged this chapter here.
Monday, 16 February 2026
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
Part I: The Environment to be Perceived
Part II: The Information for Visual Perception
Part III: Visual Perception
Chapter 9: Video || Podcast
Chapter 10: Video || Podcast
Chapter 11: Video || Podcast
Chapter 12: Looking with the Head and Eyes
Chapters 12: Video || Podcast
Chapter 13: Locomotion and Manipulation
Chapter 14: The Theory of Information Pickup and Its Consequences
Chapters 13 & 14: Video || Podcast
Part IV: Depiction
Chapter 15: Pictures and Visual Awareness
Chapter 16: Motion Pictures and Visual Awareness
Chapters 15 & 16: Video || Podcast
Saturday, 18 February 2017
The Nature of Ecological Perceptual Information
The central issue in the perception of the world is how the perceptual system comes into contact with that world. In vision, the assumption for centuries has been that the experienced world must be recovered somehow from the 2D image of the world projected onto the retina by the lens of the eye. Scientists therefore hunted for patterns on the retina that preserved critical structure from the world by copying some part of that critical structure.
James J Gibson was, for a long time, no exception to this hunt. His early empirical work (grounded in the theory he laid out in The Perception of the Visual World; Gibson, 1950) created and manipulated retinal images that, for example, contained gradients of optical texture that matched gradients of physical texture created as surfaces receded in depth, or changed their shape or orientation relative to a point of observation. But time and again, Gibson found that perceptual experience was not any straight-forward function of retinal stimulation (i.e. sensations). People did not ‘see’ what was on the retina (Reed, 1988). The most powerful demonstration of this fact is Gibson’s analysis of dynamic occlusion (Gibson, Kaplan, Reynolds & Wheeler, 1969; Kaplan, 1969) to which we will return below.
Gibson’s later career was defined by the search for an explanation of how perception could be possible if it wasn’t based on sensations and retinal images. Gibson’s solution was his theory of the ecological information available for visual perception published in The Ecological Approach to Visual Perception (Gibson, 1979).
What follows is a description of ecological information with reference to some of Gibson’s work and the extensive research literature that has taken place since Gibson’s death in 1979. The focus will be on the information in light for vision, because that has been the focus of the research. However, the principles hold for all the various energy media our perceptual systems interact with, and we will review this briefer evidence as well.
James J Gibson was, for a long time, no exception to this hunt. His early empirical work (grounded in the theory he laid out in The Perception of the Visual World; Gibson, 1950) created and manipulated retinal images that, for example, contained gradients of optical texture that matched gradients of physical texture created as surfaces receded in depth, or changed their shape or orientation relative to a point of observation. But time and again, Gibson found that perceptual experience was not any straight-forward function of retinal stimulation (i.e. sensations). People did not ‘see’ what was on the retina (Reed, 1988). The most powerful demonstration of this fact is Gibson’s analysis of dynamic occlusion (Gibson, Kaplan, Reynolds & Wheeler, 1969; Kaplan, 1969) to which we will return below.
Gibson’s later career was defined by the search for an explanation of how perception could be possible if it wasn’t based on sensations and retinal images. Gibson’s solution was his theory of the ecological information available for visual perception published in The Ecological Approach to Visual Perception (Gibson, 1979).
What follows is a description of ecological information with reference to some of Gibson’s work and the extensive research literature that has taken place since Gibson’s death in 1979. The focus will be on the information in light for vision, because that has been the focus of the research. However, the principles hold for all the various energy media our perceptual systems interact with, and we will review this briefer evidence as well.
Thursday, 7 June 2012
Specification: What It Is, and Why We Need It (Specification I)
The first thing I need to do in a discussion of specification is explain what it is and why it's important to ecological psychology. I've tried to maintain a clear logical progression in this post, building towards the need for specification. In my next post, I'll take a first swing at explaining what specification gives us, namely a reason why information means one thing and not another.
The issue of specification comes from Gibson's (1966, 1979) analysis of visual perception, so that's where I'll start too. Most descriptions of visual perception begin with the anatomy of the eye; people note that the eye resembles a camera, and that the lens seems to focus a messy, upside down image onto the retina. The retina then pixelates that image into neural activity, and this pixelated structure then shows up in primary visual cortex (this is topographic mapping). If vision does indeed begin this way, then a huge amount of work seems to be required to take this impoverished stimulus and use it as the basis for the rich, 3D visual world we experience.
Gibson's ecological theory begins with a re-evaluation of the stimulus for vision. The first three chapters of the 1979 book are about the world and what it contains, while chapter 4 is about how this world can interact with light to produce information. Only once he lays out the information available to the organism does he begin to talk about the act of perception itself; this re-evaluation of the 'job description' for a visual system is one of his most important contributions to psychology. Gibson's reanalysis leads him to conclude that action relevant properties of the world (specifically, affordances) can be specified in the optic array, and this concept underpins the directness of his theory of perception.
The issue of specification is assumed to be critical for the success of a direct theory of perception. The traditional views propose a 'many-to-one' mapping; a given pattern of stimulation on the retina is ambiguous because it could be caused by many possible states in the world. Specification is the hypothesis that there is a 'one-to-one' mapping - a given pattern in the optic array comes from one and only one state of the world. This can happen, according to Turvey, Shaw, Reed & Mace (1981) if (and only if) the creation of information about the world is a lawful process. If the projection of world into optics is underwritten by a law and thus one-to-one, then detecting the optical pattern is equivalent to detecting the property of the world: detecting the information is perceiving the world, with no additional processing work required. Perception can be direct.
A theory of direct perception will require several elements: there must be invariant structure within the endless flow across the retina that relates 1:1 to some property of the world. To be invariant, this structure must be relational, and therefore higher order. If perception is to be direct, these higher-order invariants must be detectable as a piece, and not built out of their elements in some post-perceptual process. Only if you have all this do you have the possibility of a one-to-one mapping between the world and vision, i.e. the possibility of specification.This post lays out what this all means, and how these pieces come together in ecological psychology.
The issue of specification comes from Gibson's (1966, 1979) analysis of visual perception, so that's where I'll start too. Most descriptions of visual perception begin with the anatomy of the eye; people note that the eye resembles a camera, and that the lens seems to focus a messy, upside down image onto the retina. The retina then pixelates that image into neural activity, and this pixelated structure then shows up in primary visual cortex (this is topographic mapping). If vision does indeed begin this way, then a huge amount of work seems to be required to take this impoverished stimulus and use it as the basis for the rich, 3D visual world we experience.
Gibson's ecological theory begins with a re-evaluation of the stimulus for vision. The first three chapters of the 1979 book are about the world and what it contains, while chapter 4 is about how this world can interact with light to produce information. Only once he lays out the information available to the organism does he begin to talk about the act of perception itself; this re-evaluation of the 'job description' for a visual system is one of his most important contributions to psychology. Gibson's reanalysis leads him to conclude that action relevant properties of the world (specifically, affordances) can be specified in the optic array, and this concept underpins the directness of his theory of perception.
The issue of specification is assumed to be critical for the success of a direct theory of perception. The traditional views propose a 'many-to-one' mapping; a given pattern of stimulation on the retina is ambiguous because it could be caused by many possible states in the world. Specification is the hypothesis that there is a 'one-to-one' mapping - a given pattern in the optic array comes from one and only one state of the world. This can happen, according to Turvey, Shaw, Reed & Mace (1981) if (and only if) the creation of information about the world is a lawful process. If the projection of world into optics is underwritten by a law and thus one-to-one, then detecting the optical pattern is equivalent to detecting the property of the world: detecting the information is perceiving the world, with no additional processing work required. Perception can be direct.
A theory of direct perception will require several elements: there must be invariant structure within the endless flow across the retina that relates 1:1 to some property of the world. To be invariant, this structure must be relational, and therefore higher order. If perception is to be direct, these higher-order invariants must be detectable as a piece, and not built out of their elements in some post-perceptual process. Only if you have all this do you have the possibility of a one-to-one mapping between the world and vision, i.e. the possibility of specification.This post lays out what this all means, and how these pieces come together in ecological psychology.
Friday, 9 December 2011
Some Ground Rules for a Theory of Psychology
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| Add psychology to the list |
Sabrina and I have been working on this for, well, the entire blog. It has been a place for our "brave attempt to think out loud about theories of psychology until we get some" since day one; we've been identifying problems but, just as importantly, solutions the whole time. The theory post identified the big picture problem we see in psychology; time to lay out some solutions.
Step one is to present a map of the blog, organised thematically to guide new readers to work we've already done here. This should also help map out the gaps in the approach, so we can focus on things to do next; feel free to point us to problems we can't yet address! (And yes, we know about episodic memory and language - we're working on it.) This post is not a comprehensive summary of past work - it's a map for you to use to find what we've done so far.
To summarise: in essence, and some minor details aside, we are advocating for Chemero's (2009) radical embodied cognitive science, with the addition of some elements he was missing (network science & task specific devices). Cognition is embodied, extended and held together by the direct perception of affordances and events; the result is a complex, nonlinear dynamical system that must be analysed as such. The brain is not the sole source of our behaviour, nor is it representing the world; it clearly plays a critical role in this system, though, and we propose that we'll need the tools of network science to describe what it's actually up to (Sporns, 2010). Methodologically, we must carefully characterise the task, the resources available to solve the task (which include brain, body and environment) and the information these resources create which can sustain the formation and control of an embodied solution. This method is Bingham's (1988) task specific device approach (the main piece Chemero was missing, I think).This approach applies to all and any behaviour you want to explain, including the hard stuff like episodic memory and language.
Critically, this approach, while new (and uncommon in insisting on a role for Gibson's ecological approach) isn't just something we invented: all these elements are active parts of modern cognitive science. The only new part is bringing it all under one roof, with the goal of getting on and getting some decent normal science under our belts.
Here's what we've covered so far. If you want more details on any point, click on the links!
Step one is to present a map of the blog, organised thematically to guide new readers to work we've already done here. This should also help map out the gaps in the approach, so we can focus on things to do next; feel free to point us to problems we can't yet address! (And yes, we know about episodic memory and language - we're working on it.) This post is not a comprehensive summary of past work - it's a map for you to use to find what we've done so far.
To summarise: in essence, and some minor details aside, we are advocating for Chemero's (2009) radical embodied cognitive science, with the addition of some elements he was missing (network science & task specific devices). Cognition is embodied, extended and held together by the direct perception of affordances and events; the result is a complex, nonlinear dynamical system that must be analysed as such. The brain is not the sole source of our behaviour, nor is it representing the world; it clearly plays a critical role in this system, though, and we propose that we'll need the tools of network science to describe what it's actually up to (Sporns, 2010). Methodologically, we must carefully characterise the task, the resources available to solve the task (which include brain, body and environment) and the information these resources create which can sustain the formation and control of an embodied solution. This method is Bingham's (1988) task specific device approach (the main piece Chemero was missing, I think).This approach applies to all and any behaviour you want to explain, including the hard stuff like episodic memory and language.
Critically, this approach, while new (and uncommon in insisting on a role for Gibson's ecological approach) isn't just something we invented: all these elements are active parts of modern cognitive science. The only new part is bringing it all under one roof, with the goal of getting on and getting some decent normal science under our belts.
Here's what we've covered so far. If you want more details on any point, click on the links!
Sunday, 1 May 2011
Reading Group - Gibson (1979) Chapter 6 Part 2
So, it's been four months, but here's part 2 of Gibson '79 chapter six:
Gibson believes that events are specified in the optic array, just as stationary objects are. In this part of the chapter he describes three classes of events (changes of surface layout, changes of surface colour or texture, and changes in the existence of a surface). He goes on to discuss the types of optical disturbances that can specify these events.
Gibson believes that events are specified in the optic array, just as stationary objects are. In this part of the chapter he describes three classes of events (changes of surface layout, changes of surface colour or texture, and changes in the existence of a surface). He goes on to discuss the types of optical disturbances that can specify these events.
Tuesday, 22 March 2011
Chemero (2009) Chapter 6: Information and Direct Perception
In the previous chapter, Chemero laid out his first idea as to how a radical embodied cognitive science could be a science; he suggested taking a 'dynamical stance' in which researchers use simple dynamical systems models such as the HKB to drive empirical work. In this chapter, he moves towards his more recent suggestion, namely using Gibson's ecological psychology as a theoretical basis from which to make predictions and run experiments. This is a much more robust idea; sciences need theories or else they wander from phenomenon to phenomenon, which I believe to be a real issue in modern psychology and cognitive science.
Chemero has his own flavour of ecological psychology, however. He believes it stays true to Gibson's essential framework but expands it to cope with new and important issues. The two pillars of ecological psychology, information and affordances, remain. Chapter 6 is Chemero's expanded notion of information, while Chapter 7 is his updated theory of affordances as relations (which I've covered briefly before).
Tuesday, 8 February 2011
F*cking affordances - how do they work?
Over on Bounds of Cognition, Ken has been doggedly pursuing what he thinks is a critical problem with the concept of affordances as described by Gibson (1979) and expanded on by Turvey, Shaw, Reed & Mace (1981; hence TSRM). I feel the need to spend some time consolidating my responses and some ideas in one place; every time I try to lay out why the problem is ill-posed or a potential route out, Ken just says I'm clouding or avoiding the issue or throwing out red herrings.
I actually think Ken has identified one very useful critique of the affordance concept: the lack of care with which we attach '-able' to words. But Ken isn't just making a methodological point; he thinks he's shown that affordances cannot structure light in a way that can specify the affordance, and that's the argument that needs to be tackled.
Saddle up: this is going to take some time, and I'm not going to solve everything. But to get a little ahead of myself, the answer to the problem is that it's complicated.
I actually think Ken has identified one very useful critique of the affordance concept: the lack of care with which we attach '-able' to words. But Ken isn't just making a methodological point; he thinks he's shown that affordances cannot structure light in a way that can specify the affordance, and that's the argument that needs to be tackled.
Saddle up: this is going to take some time, and I'm not going to solve everything. But to get a little ahead of myself, the answer to the problem is that it's complicated.
Friday, 14 January 2011
Reading Group - Gibson (1979) Chapter 6 Part 1
Chapter 6: Events and the information for perceiving events
Thus far, Gibson has been talking about how we perceive objects. But, things in the world often move around, so we'd better be able to perceive things that are extended in time as well. First off, Gibson describes the properties of surfaces that are relevant to events. He then identifies a number of things that can happen to surfaces during events. The nature of these changes will determine what types of optical information might specify particular events (this will be discussed in Chapter 6 Part 2).
Thus far, Gibson has been talking about how we perceive objects. But, things in the world often move around, so we'd better be able to perceive things that are extended in time as well. First off, Gibson describes the properties of surfaces that are relevant to events. He then identifies a number of things that can happen to surfaces during events. The nature of these changes will determine what types of optical information might specify particular events (this will be discussed in Chapter 6 Part 2).
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