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.

Affordances, by Gibson and TSRM
I have described the environment as the surfaces that separate substances from the medium in which the animals live. But I have also described what the environment affords animals, mentioning the terrain, shelters, water, fire, objects, tools, other animals, and human displays. How do we go from surfaces to affordances? And if there 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 constitutes what they afford.  
Gibson, 1979, p. 127.
A climb-upable thing must possess a certain rigidity, a certain surface area, a certain height, a certain textual quality, etc., to support the climbing of the snail and the snail must be of a certain mass, its mucous of a certain viscosity, its ventral surface of a certain flexibility, etc., to effect the climbing. This way of anchoring an affordance - when pursued thoroughly - is continuous with the ontological anchoring of dispositionals in general.
Turvey et al, 1981, p.264
These quotes are two ways of thinking about what affordances are. Gibson suggests they might be constituted by the composition and layout of a surface. TSRM then formalised Gibson's original description to make affordances dispositions (like the solubility of salt in water). Dispositions are anchored to the world - salt is disposed to dissolve in water because of the chemical properties of ionic salts and the electrical charges of water molecules. The anchoring properties underwrite the disposition so that it is a non-accidental property. Then, for both Gibson and TSRM, the affordance must structure the light (for vision) in such a way as to specify the affordance; this optical structure comes from the surface of objects.

The proposed problem
Ken believes that neither the "composition and layout of surfaces" or the anchoring properties of an affordance can, in fact, structure light so as to specify the affordance. The problem, as he states it, is that only surfaces can structure light, but most (if not all) affordances are actually anchored by properties beneath the surface. Therefore affordances cannot structure light and cannot be visually perceived.

The fun began with this post, in which the following basic thought experiment emerged (paraphrased):
Take two identical boxes, say 3" on each side. Now take one of these boxes and rig it so that if you come close to it, it explodes and kills you, but so that this rigging doesn't alter anything about the surface of the box.
You can now actually only pick up one of the boxes - the exploding box cannot be picked up because it explodes if you come too close. Visually, however, the two are identical; so whatever perception is detecting, it cannot be the affordance 'pick-up-ability' because only one of the boxes actually has that property and you cannot perceive a property that isn't actually there.

The exploding box example is actually fairly distracting, though, because it requires an Evil Philosopher who rigs boxes; it's directly analogous to the 'equivalent configurations' issue I've discussed with respect to the Ames Room, and Runeson provided what I think is a nicely robust rebuttal to these types of arguments. Ken's problem seems to hold holds, though, for a more straight-forward affordance such as walk-on-ability: 
If a terrestrial surface is nearly horizontal (instead of slanted), nearly flat (instead of convex or concave), and sufficiently extended (relative to the size of the animal) and if its substance is rigid (relative to the weight of the animal), then the surface affords support. It is a surface of support...it is stand-on-able...walk-on-able...run-over-able...
Gibson, 1979, p. 127
All of these anchoring properties are capable of structuring light, with the notable exception of rigidity (relative to the weight of the animal). It's not clear how the strength of the surface can structure light for visual perception. It is required to anchor walk-on-ability, however, and this is Ken's entry point.

(A side note: Ken restricts his objections to vision because a) it simplifies the problem and b) both Gibson (1979) and TSRM are primarily discussing visual perception. The first point makes this problem a straw man: shrinking the problem space to the point where the solution can't fit is cheating. That said, many of the affordances he's discussing are ones that those authors use as examples of of visually specified affordances, so the issue remains to be addressed. I'm going to insist on access to the rest of the perceptual systems, though, because it matters.)

The science of affordances
Ken's spent several posts showing pictures of things and asking whether they visibly afford anything. My answer has usually been "No idea: you should run the experiment and see". This hasn't counted as an answer, because Ken is really just trying to pile on examples of things he thinks he already has the answer for. However, there is a way to find the answer to his question, and it requires empirical research as laid out quite clearly  by Gibson. 

TSRM propose the following formal description of Gibson's empirical approach:
The analysis of an affordance as a natural kind for an animal is two stage. The first stage is very much a matter of ecological physics: to isolate occurrent physical properties that are invariant over the extension and the perspectives and which are non-accidentally related to the extension of the affordance.... The second stage in analyzing an affordance for an animal is very much a matter (for visually detected affordances) of mathematical optics: to describe the light patterned by an affordance-specific occurrent property and to characterize that patterning in terms of an optical variable, an optical property, that stands in strict correspondence to the occurrent property.
Turvey et al, 1981, p. 264-265
The two pillars of Gibsonian ecological psychology are affordances and information. For TSRM, you must first identify the relevant anchoring properties which are specific to the affordance, then identify how these properties lawfully structure (e.g) light to produce information. The lawfulness allows the information to specify the affordance.

Affordances exist; the real question for a theory of perception is whether there is information for them, and whether organisms can detect this information. The latter is demonstrated by showing that organisms organise their behaviour with respect to the affordance; the former is demonstrated by showing that this behaviour varies predictably in response to perturbations of the proposed information.

Can affordance properties structure energy arrays?
Ken isn't going to like this answer much, and to be honest it's incomplete at this point because I'm still trying to tie it all together. But the answer to the question is: it depends, and it's complicated.

1. Affordances as a subset of dispositions
Not all dispositions are affordances. In the exploding box scenario, one box is disposed to explode if someone comes too close. However, by the rules of the example, there cannot be information for this disposition - the manipulation is designed to be imperceptible. To create an imperceptible property and then claim a failure to perceive it kills a theory of perception is nonsense. I've come to think of the problem in terms of sets: there is the set of dispositions, and affordances are the subset which are about action and for which there can, in principle, be perceptual information. The disposition to explode is therefore a disposition, and not an affordance.

Ken's objection, if true, would simply mean that the set of affordances as defined here is empty because he claims there can't be information. This was just ruling out dispositions that don't impact on action, to narrow the field and rule out exploding boxes. Let's now focus on our problematic case, walk-on-ability, and think about how this can be specified.

2. Affordances are specified across both space and time, and perceived across perceptual systems
Ken tried showing images of surfaces (say, ice on a pond) and asking 'Does the surface of this pond structure light in such a way as to enable a human to visually perceive that this is walk-on-able?'. The sticking point is the issue of surface rigidity - can it bear your weight? There are several lines of attack here, which I actually think all come into play.

Vision and rigidity: The human visual system is actually surprisingly sensitive to rigidity. A surface is rigid if the distance between points is preserved over a transformation, either moving the surface or moving the point of observation. Genuinely rigid relative motion sticks out like a sore thumb. So actually, perhaps it is available to vision, although of course the key property is rigidity relative to the weight of the organism. 

What behaviour are we actually trying to explain? If you actually run the study to see what people might do, I think they'd be inclined to test the surface before committing their whole weight. So visually? Perhaps not; but there is, indeed, information available to a mobile exploring organism with multiple perceptual systems, and it's important to remember that this is what we are.

In addition, perception-action is not perfect. I talk a lot about how good the system is; I'm not interested in illusions and failures, I'm interested in our successes. But we do fail, and these failures can tell us something about how we were controlling our behaviour. We do fall into unexpected holes; we do occasionally stop paying enough attention and trip on that flat footpath; we do walk out on ice and fall over on it or through it. This is part of the actual behaviour we have to explain, and why Gibson insisted you have to do this empirically: an ecological psychology tries to explain what animals actually do.

The continuous nature of surfaces: When I am standing on a footpath and visually examining the footpath ahead for it's walk-on-ability, I can see two things: the surface ahead of me, and the fact that this surface is continuous with the surface I am currently happily walking on. I can now perceive the full affordance of this surface, but this perception occurs using multiple systems and spans current information about what I'm on as well as prospective information about future conditions.You could even, in principle, restrict this to just vision: you can visually perceive the future path, it's continuity with where you are, and the fact that you are standing and mobile. So again, perhaps vision can do the trick, but even if this doesn't quite work, we still have other information.

Continuity matters: for example, when I fell on ice and broke my wrist I was locomoting under the control of an affordance spanning a) my perception of the safe surface I was on and b) the perception of the icy patch ahead, which contains no information about friction, let alone the change in friction. To my perception-action system the surface was continuous and I acted in accordance with that perception (with disastrous consequences; but that's a separate issue). Surfaces can of course be perceptibly discontinuous, as in the case of the transition from the shore to the iced over pond. But this has consequences for behaviour - as I noted, I'm willing to bet people on the shore would alter their locomotion to explore the ice. 

Of course, I walk into work over numerous types of surface with numerous discontinuities and I don't explore every one - why not? This brings us to what I think is the often neglected third pillar of ecological psychology - perceptual learning. Neglected by modern researchers and philosophers, but not, of course, by Gibson.

Perceptual learning
I think we forget precisely how much experience we have in interacting with the world. Infants spend a huge proportion of their time learning simply to stand, then cruise, then locomote, and even once they've achieved these basics it takes years of practice, millions of steps, to become a truly expert walker. The perception-action basics (locomotion, prehension, postural control) are what we spend out entire waking lives doing and redoing. 

Add to this the modern, carpentered world. Gibson described how the natural world could be suitably reliable to support skilled, direct perception for action; I, however, live in a city designed by people for people, in which the regularities we depend on are manufactured into the system on purpose. I have extensive experience with the range of surface discontinuities I can expect in a city, and I have learned that none specify a functional discontinuity: the world may have a little break in it but to perception, that break effectively doesn't exist. Out in the more natural world, many surfaces are locally continuous for long periods, and when they aren't, it's either a discontinuity the observer has learned doesn't matter or it's a discontinuity that triggers a discontinuity in locomotion behaviour. 

The other part of perceptual learning is learning what it is the information specifies. All an organism has access to is information; the TSM laws account includes a symmetry principle which links the world to this information and (critically) the information back to the world. We learn to differentiate invariant features of energy arrays because things that persist can be learned over time; these features persist because they are lawfully generated by the ecological physics of the event or affordance; we then come to learn that this feature specifies that affordance. You can trick this system: a shark detecting a fake electrical signal might still come looking for the fish that signal specifies in it's niche. But that trick requires you to break the scope of the law the shark is depending on to underwrite the specification relation: the trick needs an Evil Biologist, and, like the exploding box case, there's no way for an organism to tell the difference. 

Organisms come to know what the information specifies by using that information to control action. That information can control action successfully because it is reliably (lawfully, in fact) present in specific circumstances: when the event or affordance is present. Laws underwrite a 100% correlation; in fact, laws are the only way to get a 100% correlation, in the long run. So organisms are sensitive to this reliability, and come to perceive what the world means over time, and all they ever have is their first person perspective: they never, ever get to peer behind the curtain.

Summary
I doubt Ken will find any of this useful. But that's not my problem. Gibson's ecological psychology has a lot of room to manoeuvre in  it, and this is not a distracting weakness. The room comes from the use of ecological laws, the recognition that perception-action is fundamentally extended over both space and time, and the recognition that we have multiple complementary perceptual systems with access to numerous energy arrays, and that a gap in one is often simply filled in by another. This is why Gibson was so insistent that laying out affordances is an empirical task: with this many degrees of freedom, there is more than one solution, and this flexibility is the reason perception and action can succeed to the degree that it does.

This is a huge post, and there's a lot in here where I've glossed over the details. All of this will come back up, so game on!

43 comments:

  1. he thinks he's shown that affordances cannot structure light in a way that can specify the affordance,

    No. I think that affordances typically do not structure light in such a way as to enable light to specify them. I've, in fact, offered a couple of examples where it seems to me that the composition and layout of surfaces does constitute an affordance. So, I think that "see-ability" and "serviceable as an occluder" might be affordances and they seem to me to be constituted by surface.

    Put a bit more forcefully, I would say that most of the examples of affordances that have been proposed by EPists are not constituted by the composition and layout of surfaces.

    ReplyDelete
  2. Ken believes that neither the "composition and layout of surfaces" or the anchoring properties of an affordance can, in fact, structure light so as to specify the affordance. The problem, as he states it, is that only surfaces can structure light, but most (if not all) affordances are actually anchored by properties beneath the surface. Therefore affordances cannot structure light and cannot be visually perceived.

    Ok. So, you are waffling here on what my view is. You get me wrong in the first sentence. See the previous comment. Then, you get it right in the second sentence. But, then you get it wrong again in the third sentence. It is that affordances typically do not structure light.

    ReplyDelete
  3. The exploding box example is actually fairly distracting, though, because it requires an Evil Philosopher who rigs boxes;

    As I mentioned in reply to Charles at my blog, the exploding boxes is just for philosophical drama. One reason I switched to more pedestrian examples such as step stools, floors, piles of white stuff, a frozen pond, etc. was to make this clearer. Alas, to no avail.

    Moreover, interested psychologists should be able to take the basic idea and fashion it into a real science experiment.

    ReplyDelete
  4. OK, 'typically don't' is fine. This doesn't prevent this being a problem if I can't address it, because if they typically don't then why would perception ever use them? Plus 'seeability' is a rubbish affordance to be allowed - I want walk-on-ability and throw-ability, etc.

    I know what the exploding box is about: part of what I'm doing here is just putting a bunch of stuff that's gone by at BoC out in the open here, and laying out how I want to deal with it. It's some tidying that needs doing, for me if no one else.

    ReplyDelete
  5. For a post of mine on the scope, see here:
    http://theboundsofcognition.blogspot.com/2011/01/maybe-some-surfaces-can-constitute-some.html

    So, the heart of the issue is whether the affordances that the EPists have often alluded to do (e.g. walk-on-ability, stand-on-ability, climb-on-ability), in fact, structure light. The argument shows they don't.

    ReplyDelete
  6. But the reply to this (from above) is light is not the only source of information; plus light might be able to give you everything you want anyway.

    So the fact that some affordances require more than vision for specification, or the possibility that some affordances in the literature actually need more than light, ceases to be that worrying. It's just "OK, we just need to take more care when we do our science", which frankly I've known for years.

    That post isn't about the scope of ecological laws.

    ReplyDelete
  7. Genna Erlikhman8 February 2011 23:42

    I'm tempted to side with Andrew with a lot of what he says, but I am sympathetic to Ken's criticism.

    If I may, I'd like to try to rephrase Ken's point and see if that helps clear anything up.

    The claim in Gibson is that surfaces, substances and the medium in the environment structure light in such a way that we can directly perceive how we can act with respect to this optic flow (what the optic flow affords). Ken's point is that we can imagine many situations where the information specified by the optic flow is exactly identical, but how you can act with respect toward it is radically different.

    To take his frozen-over-pond example, it is possible that there are two ponds that produce exactly the same optic flow when one walks around them, actually have different affordances - you can walk on one, but not on the other. Presumably, in most cases, something about the properties/texture of the surface would alert us, visually, about the thickness of the ice, but in this special situation, let's suppose that for all intents and purposes the structure of light coming off the two ponds is identical (or agnostic with respect to the thickness of the ice).

    Or, another example: a trick stool is a trick stool precisely because it looks exactly like a real stool - the way light is structured by a trick stool is identical to the way it is structured by a real stool. So there is nothing about the structure of light that corresponds to sit-on-ability in one case and lack of sit-on-ability in the other.

    The structure of the light in the ambient array is not sufficient for specifying affordances.

    Is that a fair assessment, Ken?


    I'll post a response tomorrow on Ken's blog since he's going to argue his point there himself. I want to point again to the section on "Misinformation for Affordances" where Gibson provides similar examples.

    ReplyDelete
  8. I'll let Ken defend his view. But there are several replies I can queue up:

    To take his frozen-over-pond example, it is possible that there are two ponds that produce exactly the same optic flow when one walks around them, actually have different affordances - you can walk on one, but not on the other.
    To borrow Ken's standard line against extended cognition, maybe this is possible, but it is typically not actually the case. I would argue never, because in this case, the implausibility is grounded in the incredible difficulty in creating equivalent configurations, given mobility, etc. So I have reason to make this argument beyond 'no one's come up with a good example yet'.

    The structure of the light in the ambient array is not sufficient for specifying affordances.
    Ken wants 'typically not sufficient', but my suggested visual specification for the walk-on-ability of an upcoming surface suggests this is a challenge we might be able to meet, with a little attention to the problem.

    The 'misinformation' section of Gibson's chapter 8 is indeed useful; I was re-reading it while writing this post.

    One issue of precision: the world has affordances, not optical arrays. Optic flow informs, not affords.

    ReplyDelete
  9. Gennady has the idea spot on: The structure of the light in the ambient array is not sufficient for specifying affordances.

    Andrew raises a bit of a technical nicety regarding the quantifier "typically". I mean it to range over affordances. So, it is that, for your typical affordance, it does not structure light in such a way as to enable visual perception.

    ReplyDelete
  10. However, by the rules of the example, there cannot be information for this disposition - the manipulation is designed to be imperceptible. To create an imperceptible property and then claim a failure to perceive it kills a theory of perception is nonsense.

    No, the rules of the example are that the surfaces are physically identical. From that, I am assuming that all parties agree that physically identical surfaces will structure light in the same way.

    But, there is no trick here. This is basic experimental psychology. You want to see whether subjects respond to affordances or to physical properties of the surfaces of objects (or whether these are dissociable). So, you set up an experimental protocol in which the affordances vary and the physical properties of the surfaces change. (Another method, of course, that we have not touched on, is to hold the affordances constant and vary the physical properties.)

    ReplyDelete
  11. Vision and rigidity: The human visual system is actually surprisingly sensitive to rigidity.

    But, right here is where you leave the question behind. There are two principal ways to see this. One is whether the composition and layout of surfaces typically constitutes as affordance. The other is whether affordances structure light. This is a matter of the relations between surfaces, affordances, and light.

    ReplyDelete
  12. (A side note: Ken restricts his objections to vision because a) it simplifies the problem and b) both Gibson (1979) and TSRM are primarily discussing visual perception. The first point makes this problem a straw man: shrinking the problem space to the point where the solution can't fit is cheating.

    Gibson claims affordances structure light. I am raising an objection to that. How is this attacking a straw man?

    You say, "But, oh what about the other senses?" First, appeal to the other senses is not going to help affordances structure light. That's a red herring. Second, the basic structure of the argument can be extended to, say, taste, olfaction, and audition in obvious ways. It's pretty obvious how to set up an example where the question is "Can you smell the walk-on-ability, stand-on-ability, pick-up-ability of exploding boxes?"

    ReplyDelete
  13. The sticking point is the issue of surface rigidity - can it bear your weight?

    The rigidity of a surface or object is not the same as whether it will bear the weight of a human. That is, there are rigid objects that will not bear the weight of a human.

    ReplyDelete
  14. What behaviour are we actually trying to explain? If you actually run the study to see what people might do, I think they'd be inclined to test the surface before committing their whole weight.

    But, the issue is not one of trying to explain behavior. It is about whether the composition and layout of surfaces typically constitutes an affordance. It is about the ability of affordances to structure light. This is what is at issue and it goes badly for Gibson, which is why, I suppose, you want to look somewhere else.

    ReplyDelete
  15. You want to see whether subjects respond to affordances or to physical properties of the surfaces of objects (or whether these are dissociable).
    Actually this is incorrect. You really want to see whether subjects respond to information for affordances. In your setup, there can be no information about the difference, therefore you have no basis to expect a difference in behaviour.

    Vision and rigidity: The human visual system is actually surprisingly sensitive to rigidity.

    But, right here is where you leave the question behind.
    ...
    The rigidity of a surface or object is not the same as whether it will bear the weight of a human. That is, there are rigid objects that will not bear the weight of a human.

    Yes, of course. I'm just noting that rigidity is visually available. Actually, if you can perceive that the surface stretching out continuously from where you are currently standing remains rigid then you have visual information about the future path's continued ability to support you.

    You say, "But, oh what about the other senses?" First, appeal to the other senses is not going to help affordances structure light. That's a red herring.
    I'm not claiming they structure light; I'm saying they are a source of information from non-light based energy arrays, which helps fill the gaps in vision's capacities.

    Other modalities also calibrate the perception of structure in light, so they do actually directly contribute to what visual perception perceives.

    Second, the basic structure of the argument can be extended to, say, taste, olfaction, and audition in obvious ways. It's pretty obvious how to set up an example where the question is "Can you smell the walk-on-ability, stand-on-ability, pick-up-ability of exploding boxes?"
    The real question is, of course, 'can you perceive the walk-on-ability of a surface via both vision and touch?' You're ruling out the actual answer to the question, hence it's a straw man (also just because the book is about vision doesn't mean Gibson was ever thinking vision acts in isoloation. That's an incorrect reading of Gibson 1979, and you should read Gibson 1966 if you still think it's a valid point).

    But, the issue is not one of trying to explain behavior. It is about whether the composition and layout of surfaces typically constitutes an affordance. It is about the ability of affordances to structure light. This is what is at issue and it goes badly for Gibson, which is why, I suppose, you want to look somewhere else.
    The issue is entirely about explaining behaviour. This is where Gibson's insistence that this is all an empirical enterprise comes in, and why: the job of the ecological psychologist is to figure out the information supporting the behaviour that the organism is actually doing. It is not to lay out a priori a bunch of plausible affordances.

    You think you've cut in one step ahead of this and ruled out the possibility of there being information to be used (typically). But that's because you're artificially restricting the solution space to just vision, which is an error and a cheat. And, even if there was only vision, there are straight-forward analyses that reveal information for properties like the walk-on-ability of surfaces (as I show above as an example).

    You have to run this empirically: you identify what the behaviour is, and what the relevant affordances are. You then identify candidate information variables and test whether people are detecting these. Some of these will be available just through vision; some will require other modalities. The whole enterprise either works or it doesn't; that's why it's science.

    This fascination with 'structures light' is the red herring. The solution is that perception has plenty of information to work with (optical, acoustic, haptic, etc) and it's up to us eco-psych researchers to identify what organisms use to achieve specific tasks.

    ReplyDelete
  16. Here's an attempt to address Ken's concerns while resttricting the available information to that contained in light reflected from surfaces. The bottom line is, as always for me, that what I take to be the currently assumed definition of "affordance" needs tweaking.

    I understand "persistence" and "exist" with respect to affordances to include the condition that there must be at least one actor in some environment for which an affordance is both perceivable and actualizable. If that's correct, the logical argument against the boxes example is:

    The surface of the exploding box can't structure light so as to offer the affordance pick-up-able since that action is not actualizable by any actor in any environment with respect to that box. Ie, if an actor perceives the exploding box as pick-up-able, that is simply a misperception of that affordance. Misperceptions must be allowed in any proposed analytical methodology for perception, a process inherently subject to mistakes. If some actor perceives the other box as affording pick-up-able, it nevertheless may not be pick-up-able by that actor because of some other aspect of the scenario. Again, a misperception may occur.

    In order to attack cases in which a surface indisputably structures light so as to offer an affordance to some actors, I'll start with part of Genna's comment above:

    The claim in Gibson is that surfaces, substances and the medium in the environment structure light in such a way that we can directly perceive how we can act with respect to this optic flow ...

    This as an important reminder that Gibson's objective is to construct a theory of continuous perception and action by an actor in an environment. But then Genna continues:

    we can imagine many situations where the information specified by the optic flow is exactly identical, but how you can act with respect toward it is radically different.

    I think that last phrase is misleading in a subtle way. The actor must act precisely the same in the two situations up to the time at which the information received from that "optic flow" diverges. It's perhaps clearer in the essentially equivalent situation in which two actors perceive a pond as step-on-able and walk-on-able but the pond will support one but not the other. Both actors perceive and actualize step-on-able, at which time the consequences cause their optic flows - and therefore "how they act" - to diverge. Although both correctly perceived the affordance step-on-able, one actor misperceived the affordance walk-on-able and breaks through the ice; the other takes a second step, thereby actualizing walk-on-able. Each continues to act in accordance with subsequent perceived affordances.

    Note: I have implicitly defined step-on-able a particular way for brevity. One could add more intermediate affordances - place-foot-on-able, shift-weight-onto-able, etc, etc. But since the process is actually continuous, any subdivision is for ease of discussion only.)

    Given the apparent need to include the idea of (inevitable) misperceptions, there seem to be two options: declare that need fatal to Gibson's project; or redefine "affordance" to accommodate it.

    ReplyDelete
  17. Here's an attempt to address Ken's concerns while resttricting the available information to that contained in light reflected from surfaces.
    Why? Broad access to multiple sources of information is critical to the success of perception, visual or otherwise.

    I think that last phrase is misleading in a subtle way. The actor must act precisely the same in the two situations up to the time at which the information received from that "optic flow" diverges.
    True. If the information is identical, behaviour will be too. Of course, it's quite had to get this type of 'equivalent configuration' too, given the high dimensionality of the information space; this again is critical to the success of perception.

    Given the apparent need to include the idea of (inevitable) misperceptions, there seem to be two options: declare that need fatal to Gibson's project; or redefine "affordance" to accommodate it.
    Or remember that Gibson has got there already, talking about misperception of affordances in Chapter 8. The problem is at the information level, not the affordance level - misperception is what happens when a surface doesn't create the necessary information (eg the visual cliff) or when that information is detected poorly (by a novice, or in a drunken haze, or during a lapse of attention, or what-have-you.)

    I don't see why anything needs redefining. It feels like you're forgetting about the role of information.

    ReplyDelete
  18. "Why?"

    Because since I see no convergence between you and Ken, I decided to try and abide by his rules - no "evasions", no "red herrings", etc - and see how far I could get while sticking to vision but keeping as close as possible to what I understand to be the formal definition of "affordance".

    So, the comment was really written for Ken's benefit - a thought experiment, so to speak. And I conclude - rightly or wrongly - that the essence of Gibson's project can be salvaged even with vision-only information in the very simple scenarios Ken is postulating by doing some seemingly minor tweaking. Perhaps I misunderstood the Gibson Ch 8 passage Genna quoted, but I read it as his admitting that either some tweaking of the definition or some dismissing of problematic cases was required.

    "It feels like you're forgetting about the role of information."

    I can't imagine why. I used the very word twice in the comment, the whole second point was specifically about information, and it's not obvious to me that anywhere I used "affordance" would be clarified by referring to its relationship to the information in the structure of light.

    ReplyDelete
  19. Because since I see no convergence between you and Ken, I decided to try and abide by his rules - no "evasions", no "red herrings", etc - and see how far I could get while sticking to vision but keeping as close as possible to what I understand to be the formal definition of "affordance".
    Fair enough. I've decided it's the wrong set of rules, so I'm not going to grant that ground any more. But don't let that stop you :)

    There seem to be several conflated things in your 'tweaking':

    The surface of the exploding box can't structure light so as to offer the affordance pick-up-able since that action is not actualizable by any actor in any environment with respect to that box.
    I don't think this is quite right. It can structure the light - it clearly does, as it is visible. That structure specifies that the box is pick-up-able - the point of the example is that a person would indeed try to pick it up. The fact that the affordance is not actually actualisable isn't the right place to look; this is the third person analysis, not the first person. This is what was making me feel you weren't using information; the problem arises because the first-person perspective only has access to information, and in this Evil case the information is actually misinformation (Gibson, p. 142).

    Misperceptions must be allowed in any proposed analytical methodology for perception, a process inherently subject to mistakes. If some actor perceives the other box as affording pick-up-able, it nevertheless may not be pick-up-able by that actor because of some other aspect of the scenario. Again, a misperception may occur.
    Yes, yes and yes. Part of my problem was, I think, I don't quite see these two sections matching up.

    I still don't see that affordances need tweaking; the required room to manoeuvre seems to exist, in information.

    ReplyDelete
  20. "It can structure the light - it clearly does, as it is visible. That structure specifies that the box is pick-up-able"

    Yes, and Ken argues that the information in the light from one box specifies an affordance, but the very same information from the other box doesn't. Which strongly suggests to me that the assumed definition of affordance is in serious need of tweaking.

    I have found that problems seem to go away if the various actualization requirements are relaxed, reinterpreted, or possibly even eliminated. Eg, in this case the problem is that one can't actualize a misperceived affordance. But given that actualization is the final step (actually, instant) in a possibly very long perpetual path, the need for every perceived affordance to be actualizable isn't obvious to me. Failure to actualize an intermediate affordance will interrupt the planned actualization path, but so what? That's the way things work in "real" life. And isn't that the analytical target?

    I have asked myself what might have motivated those requirements and am led back to the analytical model. In that dynamic system, at all times at least one perceived immediately actualizable affordance must be actualized in order for the model to keep running. Could the requirement of immediate actualization be merely an artifact of the model rather than a logical necessity?

    ReplyDelete
  21. Genna Erlikhman10 February 2011 23:51

    I agree with some of your points, Andrew, but I think you still miss some of Ken's objections. Namely, he's asking whether there is enough information to unambiguously determine what actions the environment affords (sorry for my loose wording earlier where I inadvertently wrote that the optic array affords). He is claiming that short of seeing someone/thing else explode, there is no way of telling apart the two boxes and this is because whether they are pick-up-able or not is not determined by their surface properties, but by their "inner" (unobservable?) properties. Critically, it's not just a matter of lack of information; that's an epistemic point about whether an observer can determine whether the box is pick-up-able or not. Ken's argument is that no amount of information of any kind can specify that one box is pick-up-able and the other isn't. This is why Charles is suggesting that we work with what counts as an affordance instead of what counts as information.

    Andrew, here is a more plausible example, maybe, than identical ponds and boxes: Suppose I have a Zippo lighter that is light-able. Today it ran out of fuel; it is no longer light-able. What has changed about the information from the surfaces of the lighter that has changed what the object affords? "containing fuel" doesn't seem to be something that we can extract directly from the optic array. Or, if you don't like this example, suppose I have a car which is drive-able, but a contact somewhere in the car comes loose and it can no longer start - it no longer affords driving. What about the surface properties of the car has changed to constitute this change in affordance?

    I'm sympathetic to Charles' approach, but I don't think we need to give up as much as he suggests. I'm about to post more on this on Ken's blog once I get my argument in order.

    ReplyDelete
  22. Yes, and Ken argues that the information in the light from one box specifies an affordance, but the very same information from the other box doesn't.
    And this is, I think, an error. The only difference between the two boxes is imperceptible; as far as perception is concerned, therefore, there is no difference. Both boxes offer the same opportunity for behaviour; one just also (imperceptibly) offers death as a consequence.

    Ken thinks that because the box can't actually be picked up, it cannot offer that affordance. And if it can't, then a box that produces identical information can't either. But this 'fact of the matter' about the exploding box is unavailable, and embedded in a set of properties that do, in fact, offer the possibility of prehension.

    This is where, to me, the possibility for error that you (rightly) want can fit in: and the section in Chapt 8 on misperception of affordances is in this vein.

    But given that actualization is the final step (actually, instant) in a possibly very long perpetual path, the need for every perceived affordance to be actualizable isn't obvious to me.
    Me neither. I'm putting the 'error' into information, and not the world. This is, I think, the difference between what we've each been advocating (please correct me if that's not right :)

    Failure to actualize an intermediate affordance will interrupt the planned actualization path, but so what? That's the way things work in "real" life. And isn't that the analytical target?
    Indeed. But my interest (and, I think, Gibson's) was to put the perceiver back in the driving seat. The question is always 'what does the organism currently know, and what is the information for that?'. It's not 'what does the experimenter think they know?', which is a very easy trap to fall into.

    Actualisation requirements: I think the issue of 'compulsory effecting' is readily accounted for with task specific effectors (I am not always a 'locomotion device'). I think that once I am such a device, I do indeed locomote compulsorily - but that's what I want! I think then, that the 'immediate actualisation' requirement isn't one. I'm trying to think if I've said otherwise; I've lost that thread, a little I think.

    ReplyDelete
  23. Ken's argument is that no amount of information of any kind can specify that one box is pick-up-able and the other isn't.
    Actually Ken's argument is currently about visual information. So I'm not missing the objection: I'm denying it's a relevant point, because
    1. visual perception can inform us about things like the rigidity of a future path; and
    2. even if it can't for some reason, we have other modalities - this is what they're all for, to complement and calibrate each other; and
    3. even if they all fail and there's no information for something, that's ok too - it's just something the system can't perceive, and that happens all the times (this is why minefields work).

    This, then, is why I'm more interested in laying out information than tweaking affordances: because I am denying, with reasons, Ken's entire argument as being of any concern to ecological psychology. It can't motivate a tweak if we already have an answer (actually thanks for your comment, this has clarified this point for me :)

    So with respect to your two examples, the lack of visual information doesn't bother me. Take the Zippo: you can
    1. shake it, and visually perceive that it moves like an empty lighter; or if that doesn't work
    2. heft it, and perceive it's too light, or if that fails
    3. you don't notice your Zippo is out.

    Or you could just try to strike it, and visually perceive that the flame isn't catching.

    I'm suggesting that there are either solutions to specific problems and you can perceive the property (which is why Gibson said run the study one task at a time), or there isn't a solution and you can't perceive the property (e.g. the friction of an upcoming surface). None of this bothers me in the slightest any more.

    I hope this makes sense - keep the questions coming, they're helping my thinking a lot :)

    ReplyDelete
  24. "This is, I think, the difference between what we've each been advocating (please correct me if that's not right"

    Not quite. Keep in mind that I'm in no position to "advocate", just to learn. So, my arguments are mostly in devil's (non)advocate mode.

    In principle, I agree that an imperceptible feature of an environment shouldn't play a role in a theory of perception (and suggested that early on). But I'm happy to explore alternatives and see how they work out. It appears that relaxing some actualization constraints deflects some of Ken's attacks, and I don't yet see the necessity not to relax them. But, I eagerly await Genna's knowledgeable exposition along those lines.

    ReplyDelete
  25. Nicola Campbell18 March 2011 13:44

    Linking affordances to evolution by natural selection, it leads me to believe that an affordance is indeed some type of objective property. If we look at evolution, man is surrounded by objects that he is using to make himself better and stronger. I am still a little cloudy when Chemero expresses that "[A]n affordance is neither an objective property nor a subjective property; or it is both if you like.(p. 136)" My question would then be, how could an affordance not be something objective or subjective just because one would wish it wasn't? And if so what would it be?

    ReplyDelete
  26. That quote is from Gibson (1979). Gibson was trying to explain what affordances are. His problem was the the traditional way to carve the world up doesn't work. You would traditionally classify things as objective (out in the world, abstract, not dependant on a perceiver - like mass) or subjective (in the mind, relative to an observer - like how tired you are). Affordances don't fit this scheme - they have to be real and 'out there' in the world, but they also have to be about the observer.

    So:
    My question would then be, how could an affordance not be something objective or subjective just because one would wish it wasn't? And if so what would it be?
    Gibson isn't saying 'if you like' to suggest you get to choose that it's both. He's suggesting that you can choose to say an affordance is neither objective or subjective, or you can say it's both. He's suggesting that because affordances don't fit the framework, it doesn't matter which way you say it because they're both about as inaccurate as each other.

    Basically, Gibson was trying to describe something in a new way for which there were no obvious terms he could borrow. So he did what he always did, and just tried to lay it out as clearly as he could. Turvey et al then suggested that a formal framework that could be used to be more specific was that of dispositions; Chemero is suggesting that the formal frame work should be relations. Both are attempts to fit Gibson's ideas into a more organised, less mysterious sounding framework. Gibson just didn't have either of these vocabularies as options.

    ReplyDelete
  27. What Andrew said!
    The missing piece of the puzzle, which Harry Heft has developed, but could developed further, is the connection of Gibson's work to William James's work. This style of rejecting the subjective/objective distinction is unquestionably a result of Gibson's exposure the American philosophical tradition. E. B. Holt (the intellectual intermediary between James and Gibson) would have talked in terms of "cross sections", and John Dewey would have used similar examples without that particular term. To hazard an example: If you see the chair in my room as contextualized by the other furniture in my office, it is a part of the room, and as objective as anything else. If you see the chair in my room as contextualized by the flow of other things you have seen when on campus today, then it is part of your consciousness, and as subjective as anything else. But there is only one chair! It is "neither objective nor subjective, or it is both if you like."

    Andrew says that, Chemero says that, we need to talk about relations. This is the reason that one of the main agenda items of the New Realists (1910, 1912) was to argue for the reality of "relations." It is a necessary battle point for this lineage of American Philosophy.

    One thing I hope to convince people of (especially Chemero) is that Holt worked out the philosophical basis for much of this stuff already. True, Holt's work had holes that have been filled by empirical evidence (which Chemero's book makes very clear). But the basic metaphysics and epistemology are there; we could save a lot of time by resurrecting instead of reinventing.

    Sigh... I'm rambling again.

    ReplyDelete
  28. I was quite interested in Heft on Holt. I thought making that connection to James via Holt made a lot of things make a lot of sense. Affordances sound whacky to modern ears and grounding it helps a lot.

    ReplyDelete
  29. Ken and Andrew and Charles and Genna,
    I have just caught up with all your backs and forths here. I would say that many eco psych people promote a more extreme vision that Gibson did, and that such leads to these problems. There are much more reasonable positions that I think avoid a lot of these issues. The more reasonable position goes something like this:
    There are patterns in ambient energy. Some of those patterns are specific to properties of world. So not all properties of objects are specified by "information", but some are. Some of those properties that ARE specified determine whether or not objects are useful in this way or that way to certain types of organisms. Some organisms are designed to respond to those particular patterns of energy.

    That's all you need. Not all patterns are information. Not all information is about affordances. Not all affordances structure information. No existing organism can detect all the information that would be useful to it even in theory, nevertheless in practice. But sometimes it all works out, and in those situations organisms perceive affordances.

    -----

    P.S. Note that in many cases Gibson thought the visual perception of an affordance was dependent upon continuous exploration or fortuitous other events. For example, it is much easier for me to perceive that a frozen lake can support my weight if I see a car drive across it first. Gibson ('79 I believe) had an illustration where you perceive that a surface is flexible because it deforms around a ball. Absent the ball, a complete third party, the flexible and inflexible surfaces are visually identical. -- I am convinced that this relates very, very closely to Charles Sanders Peirce's notion of a truth seeking via self-correcting mechanisms (in contrast to Descartes's truth seeking via error avoidance mechanisms), but have yet to find a Peirce scholar with the time to pursue that with me. -- Making mistakes is just not a problem for Gibson, as long as it is correctable. Some modern Eco-Psych people, for some reason, seem to want to deny the existence of mistakes.

    ReplyDelete
  30. Not all patterns are information. Not all information is about affordances. Not all affordances structure information. No existing organism can detect all the information that would be useful to it even in theory, nevertheless in practice. But sometimes it all works out, and in those situations organisms perceive affordances.
    There are some questions lurking here, though:

    1. If a pattern is not information, what is it? Why is it present? (Note: to be a reliably present spatiotemporal structure, you need to be underpinned by a non-accidental connection between the event and the information)

    2. Any affordance that doesn't create information is not perceivable and therefore, to me, a mere disposition, not an affordance.

    Gibson ('79 I believe) had an illustration where you perceive that a surface is flexible because it deforms around a ball. Absent the ball, a complete third party, the flexible and inflexible surfaces are visually identical.
    Well yes - but this is not a problem. It's just highlighting that two things which are not perceptibly different will not be perceived as different. This is why exploration is so key - two things which are actually different generally give their secrets up over time.

    Making mistakes is just not a problem for Gibson, as long as it is correctable. Some modern Eco-Psych people, for some reason, seem to want to deny the existence of mistakes.
    This I agree with; it's the vibe Ken picked up on, I think. My hunch has always been that we get into this mode because we spend so much time talking about how good perception is, rather than how flawed (eg illusions). It is a problem to keep tabs on, for sure.

    ReplyDelete
  31. Not sure whether to continue this thread or not, but since you were nice enough to reply :- )

    1) So far as I can tell, the formula is that those patterns that specify are called "information." That is, ecological psychologists are particularly interested in some subset of the structure of ambient energy. In fact, one of the most common developmental problems that ecological psychologists should be willing to acknowledge are people being attuned to patterns that are ultimately ambiguous. Every time a "higher-order invariant" that specifies a property (i.e., is information), we are implicitly identifying a cornucopia of patterns that do not specify the property of interest.

    2. If affordances are opportunities for action, defined independent of our ability to perceive them (so we don't end up in a circular-definition mess), then it should be obvious that I do not perceive all possible opportunities for action (if only due to my limited sensory apparatus). For example, I can be an effective shield against microwave radiation; there are many situations in which useful options are apparent if you can detect polarized light; etc..

    2b) This point was in direct response to Ken's nice challenges. He points out that there are many situations in which I cannot perceive an affordance, because two situations dramatically different in affordances could be visibly identical. The exploding box problem is highly artificial (and hence harder to respond to), but the "can the ice support my weight" problem seemed more tractable. I was just pointing out that in a third-part-less situation, there might well be no way for me to determine this one way or another. However, even WITHOUT my personal continuous exploration, if there were other things interacting with the ice, then the information might still be present in the visible (and audible) events for me to determine if the ice could support me. -- Indiana Jones perceives that he can walk over the gorge... after he throws rocks onto the otherwise invisible path.

    ReplyDelete
  32. Comment away, it's why we're here :)

    In fact, one of the most common developmental problems that ecological psychologists should be willing to acknowledge are people being attuned to patterns that are ultimately ambiguous. Every time a "higher-order invariant" that specifies a property (i.e., is information), we are implicitly identifying a cornucopia of patterns that do not specify the property of interest.
    I'm actually not convinced that's true. Information variables are stable (over space and time) features of a given task - they are stable because of the stability of the thing they are specifying. Things that don't specify anything won't, typically, be stable enough to serve as the target of perceptual learning. Did you have any examples in mind?

    Indiana Jones perceives that he can walk over the gorge... after he throws rocks onto the otherwise invisible path.
    In fairness this is 'personal continuous exploration', but your point is still interesting. The only thing to be careful with is that you don't want to include 'knowledge of the weight of cars' in the mix if you want perception of the affordance to be direct. The car has to be generating information about the rigidity of the surface. So long as you can tell that story, it's still direct.

    ReplyDelete
  33. Andrew,
    Regarding development, a pattern that is not stable is still a pattern. "Go" boards are full of ever changing patterns, only some of which are relevant to an experienced player trying to win a game. (I am trying to invoke the literature trying to define "expertise" as being attuned to the relevant patterns, which implies non-experts are responding to non-ideal patterns.)

    Also, we both agree that features that are not stable SHOULD not, in the long run, be attuned to. But of course there are a myriad of ways that people screw up during the process of learning, and some unlucky bastard will happen to have an "unstable" pattern present each of the first 10 times he tries whatever task you are interested in (see, Skinner's related work on superstition in the Pigeon, or any good book about the challenges of becoming a professional poker player). This problem is made more obvious (or solved) by the notion of locally contextualized information in Chapter 6 of Chemero's book. If you push the idea of local constraint to far, however you will end up in solipsism.

    P.S. Yeah, I cheated a bit on the Indiana Jones example...

    ReplyDelete
  34. Hmmm... I had a well written response, but cyberspace ate it. Rough version:

    We both agree that, in the long run, no one should attune to unstable patterns. Put development often occurs over a limited number of trials under highly variable conditions. Of course people, at least temporarily, attune to irrelevant information! Some poor schmuck trying to learn a new skill will have the same not-stable pattern there the first 20 times he tries the task. The 21st time, we would be unsurprised to find him attuned to the wrong information.

    This relates to Skinner's work on "superstitious behavior," all the work trying to define expertise as attunement to the proper information, and any decent book about the challenges of becoming a good poker player.

    P.S. Yeah, I cheated the Indy example.

    ReplyDelete
  35. Uhg... "information" is defined as relevant, so when I said "irrelevant information," I meant "the wrong patterns."

    ReplyDelete
  36. Uhg, even that isn't good enough. Let me try again. Sorry for the repeat postings, I'm not sure what proper Blog etiquette is this situation.

    ----


    We both agree that, in the long run, no one should attune to unstable patterns. Put development often occurs over a limited number of trials under highly variable conditions. Of course people, at least temporarily, attune to patterns that are do not (in the long term) specify the relevant world properties! Some poor schmuck trying to learn a new skill will have the same not-stable pattern there the first 20 times he tries the task. The 21st time, we would be unsurprised to find him attuned to the wrong pattern.

    This relates to Skinner's work on "superstitious behavior," all the work trying to define expertise as attunement to the proper information, and any decent book about the challenges of becoming a good poker player.

    P.S. Yeah, I cheated the Indy example.

    ReplyDelete
  37. Sabrina and I have actually been talking about this recently. Genuinely unstable patterns simply can't serve as a target for perceptual learning; that's fine. The question then is, can you learn to use a non-specifying variable due to some kind of sampling limitation - a local minimum problem, in effect.

    I tend to think yes, but only if the non-specifying variable specifies over some sufficiently stable range, just not the full range. I'm happy to acknowledge that we have limited time and exposure and that within the range of our exploration, there may be something that is 'good enough' that we can learn to use. But if you expose the limited scope of the variable, and there is a better variable with a more robust scope, I predict you'll quickly switch. I actually have a plan to test this idea over the next year.

    So, yes, it's definitely interesting. And, as Gibson pointed out, an empirical enterprise.

    ReplyDelete
  38. Well, but there is a lot of research about this in behaviorism land. If you train an animal with a mediocre indicator, and then introduce a completely reliable indicator, they will be very slow to switch, if they switch at all. You can even get the same effect with both indicators present at the start, if you make the mediocre indicator more "salient" (a term that is likely circular in this usage).

    I think that if you try to stick narrowly to behaviors that lend themselves to very concrete, linked perception-action analysis, then your position might hold. But if you expand to other behaviors, the troubles I am mentioning will become readily apparent. How does a race car driver decide whether to pass, and if so, whether to pass on the inside or outside line? Is there really a perfect higher-order invariant available for such a decision? There might be! Certainly we could constrain the race rules to the point where a stable higher-order invariant would emerge. But even if we did, what are the odds that ALL race car drivers would attuned to exactly that? Even if they all would eventually (which I doubt), how many races would it take? Would it be that surprising to find experienced, successful driver who passed opponents based on a good, but not perfect set of rules? (Answer: If all drivers were identical, no one would watch races, so there must be differences.)

    ReplyDelete
  39. I realized I was conflating affordances & dispositions earlier, & I think Eric's summary of Ken's argument shows the same mistake:
    "[Ken] points out that there are many situations in which I cannot perceive an affordance, because two situations dramatically different in affordances could be visibly identical."

    It's not true to say that you will fail to perceive an affordance. The ability of the box to explode is a disposition, not an affordance. The point is that you will *always* perceive an affordance -- but this affordance will not reflect the disposition in question if there is insufficient information.

    We need 4 terms to describe what happens: the disposition, the associated properties which provide the information, the information itself, and the perceived affordance. Is there already a concise term for those associated properties? If not, I propose the term 'indicators.' (The set of indicator properties may overlap the set of disposition properties, or they may be disjoint.)

    So when we learn, we develop some way of perceiving affordances via the information provided by the indicator properties, which are presumably correlated to the dispositional properties in question. (And then we develop ways of behaving given the perception of the affordances.) This gets interesting when the correlation between the indicator properties and the dispositional properties is low: take the case of 'coefficient of friction' as the disposition and 'surface reflectance' as the indicator property - not completely correlated.

    Or even more interesting: when do we consistently rely on indicators that are not optimal, and why? That ought to tell us what kind of information/indicators we are (evolutionarily) primed to home in on.

    I'm struck by an analogy between the concepts of affordances/dispositions here, and the idea of utility in economics. Utility is supposed to be a quantification of the subjective value of a good or service. For example, the typical example of the law of diminishing returns (ie, you get less enjoyment out of the 4th donut you eat than the 1st) rely on the concept of utility. They were basically trying to quantify the qualitative, and of course it doesn't work perfectly.

    ReplyDelete
  40. Well, I should have read the rest of the comments -- looks like Eric has already adopted the term indicator!

    ReplyDelete
  41. 'Indicator' properties have a name; they are the anchoring properties of the disposition. Turvey et al (1981) talk about this in some detail, but I only came across the idea arguing with Ken. They come in damn handy though.

    See the Turvey et al quote above, and this bit from me:
    Dispositions are anchored to the world - salt is disposed to dissolve in water because of the chemical properties of ionic salts and the electrical charges of water molecules. The anchoring properties underwrite the disposition so that it is a non-accidental property.

    These are different from 'mere' indicators. Dispositions are composed of anchoring properties; dispositions are emergent properties, relations between anchoring properties. The anchoring properties are the physical things that structure light and create information; the disposition is what that structure specifies.

    If the property merely correlates (eg shine with friction) then the former cannot be an anchoring property of the latter. Then you might want to use the word indicator; but their status in ecological psychology is uncertain at best. It's not clear that what they create counts as information. That is a complex topic though.

    ReplyDelete
  42. Great blog and discussion.
    Anyone keen on taking this Call for Papers on?...
    Bridging the theories of affordances and limb apraxia: http://www.frontiersin.org/Human_Neuroscience/researchtopics/Bridging_the_theories_of_affor/2039
    Seems they need some help on the basics of affordances; we do know what they are, right?

    ReplyDelete
    Replies
    1. Hi Paul; it's been a long time, I hope all is well!

      The topic looks interesting; I don't know a whole lot about apraxia but I applaud the idea of getting into affordances to explain how it plays out. I'll certainly think of submitting if I can find a co-author who do the apraxia end.

      Delete