Gibson on Information and Misinformation 2

Let me note another feature of the following:

It is because the affordances of things for an observer are specified in stimulus information. They seem to be perceived directly because they are perceived directly.

…

The central question for the theory of affordances is not whether they exist and are real but whether information is available in ambient light for perceiving them.  The skeptic may now be convinced that there is information in light for some properties of a surface but not for such a property as being good to eat. The taste of a thing, he will say, is not specified in light; you can see its form and color and texture but not its palatability; you have to taste it for that.  (Gibson, 1979, p. 140)

MISINFORMATION FOR AFFORDANCES

If there is information in the ambient light for the affordances of things, can there also be misinformation? According to the theory being developed, if information is picked up perception results; if misinformation is picked up misperception results.

The brink of a cliff affords falling off; it is in fact dangerous and it looks dangerous to us. It seems to look dangerous to many other terrestrial animals besides ourselves including infant animals. Experimental studies have been made of this fact. If a sturdy sheet of plate glass is extended out over the edge it no longer affords falling and in fact is not dangerous, but it may still look dangerous. The optical information to specify depth-downward-at-an-edge is still present in the ambient light; for this reason the device was called a visual cliff by E. J. Gibson and R. D. Walk (1960). Haptic information was available to specify an adequate surface of support, but this was contradictory to the optical information. When human infants at the crawling stage of locomotion were tested with this apparatus, many of them would pat the glass with their hands but would not venture out on the surface. The babies misperceived the affordance of a transparent surface for support, and this result is not surprising.

Similarly, an adult can misperceive the affordance of a sheet of glass by mistaking a closed glass door for an open doorway and attempting to walk through it. He then crashes into the barrier and is injured. The affordance of collision was not specified by the outflow of optical texture in the array, or it was insufficiently specified. He mistook glass for air. The occluding edges of the doorway were specified and the empty visual solid angle opened up symmetrically in the normal manner as he approached, so his behavior was properly controlled, but the imminence of collision was not noticed. A little dirt on the surface, or highlights, would have saved him.

These two cases are instructive. In the first a surface of support was mistaken for air because the optic array specified air. In the second case a barrier was mistaken for air for the same reason. Air downward affords falling and is dangerous. Air forward affords passage and is safe. The mistaken perceptions led to inappropriate actions.  (Gibson, 1979, p. 142)

In the first passages on p. 140, one implicitly knows how affordances are supposed to structure light, then one can use this to predict what a subject will perceive.  On p. 142, however, one has cases in which the prediction is that the affordance for "walk-on-ability" and "walk-through-ability" should structure light in such a way as to have babies go over the "invisible cliff" or have adults not walk into the glass occluder.  Yet, rather than acknowledging the failed predictions, Gibson instead postulates information in the light the will save the phenomena. This is the kind of move that Fodor and Pylyshyn were complaining about when saying that the notion of what is directly perceived is unconstrained.  It's the kind of problem that TSRM hint that they are trying to solve, but which I have been arguing they do not.

Gibson on Information and Misinformation 1

From Gibson, 1979, Chapter 8:

It is because the affordances of things for an observer are specified in stimulus information. They seem to be perceived directly because they are perceived directly.

…

The central question for the theory of affordances is not whether they exist and are real but whether information is available in ambient light for perceiving them.  The skeptic may now be convinced that there is information in light for some properties of a surface but not for such a property as being good to eat. The taste of a thing, he will say, is not specified in light; you can see its form and color and texture but not its palatability; you have to taste it for that.  (Gibson, 1979, p. 140)

MISINFORMATION FOR AFFORDANCES

If there is information in the ambient light for the affordances of things, can there also be misinformation? According to the theory being developed, if information is picked up perception results; if misinformation is picked up misperception results.

The brink of a cliff affords falling off; it is in fact dangerous and it looks dangerous to us. It seems to look dangerous to many other terrestrial animals besides ourselves including infant animals. Experimental studies have been made of this fact. If a sturdy sheet of plate glass is extended out over the edge it no longer affords falling and in fact is not dangerous, but it may still look dangerous. The optical information to specify depth-downward-at-an-edge is still present in the ambient light; for this reason the device was called a visual cliff by E. J. Gibson and R. D. Walk (1960). Haptic information was available to specify an adequate surface of support, but this was contradictory to the optical information. When human infants at the crawling stage of locomotion were tested with this apparatus, many of them would pat the glass with their hands but would not venture out on the surface. The babies misperceived the affordance of a transparent surface for support, and this result is not surprising.

Similarly, an adult can misperceive the affordance of a sheet of glass by mistaking a closed glass door for an open doorway and attempting to walk through it. He then crashes into the barrier and is injured. The affordance of collision was not specified by the outflow of optical texture in the array, or it was insufficiently specified. He mistook glass for air. The occluding edges of the doorway were specified and the empty visual solid angle opened up symmetrically in the normal manner as he approached, so his behavior was properly controlled, but the imminence of collision was not noticed. A little dirt on the surface, or highlights, would have saved him.

These two cases are instructive. In the first a surface of support was mistaken for air because the optic array specified air. In the second case a barrier was mistaken for air for the same reason. Air downward affords falling and is dangerous. Air forward affords passage and is safe. The mistaken perceptions led to inappropriate actions.  (Gibson, 1979, p. 142)

In comments on a post from weeks ago, Gennady Erlikmann draws our attention to some important texts from the latter portions of Chapter 8 of Gibson, 1979.   Now, it seems to me that the passages from p. 140 cited above champion the view that affordances structure light in such a way as to enable the affordances to be perceived.  And he does not there back off the view.  But, then on p. 142, he apparently does back off of this apparently admitting that sometimes affordances do not structure light in such a way as to enable them to be perceived.  (That's the italized part in paragraph 3 from p. 142.)  In the final paragraph, the two italicized sections suggest that the glass in the two cases did not structure light in such a way as to specify an affordance of, say, "stand-on-ability" or "walk-through-ability".  Instead, the glass apparently specified something else, namely, air.  Kind of grudging admissions.

Nevertheless, however true all this may be, the basic affordances of the environment are perceivable and are usually perceivable directly, without an excessive amount of learning. The basic properties of the environment that make an affordance are specified in the structure of ambient light, and hence the affordance itself is specified in ambient light. Moreover, an invariant variable that is commensurate with the body of the observer himself is more easily picked up than one not commensurate with his body.  (Gibson, 1979, p. 143).

In the final paragraph here, Gibson suggests that, while maaaybe not all affordances are perceived, at least all the basic affordances are perceived. 

Now, I've been trying to give examples showing that this kind of analysis will not work.  The box and the exploding box are physically the same on the outside, so structure light in the same way.  There is no room to say that one of these structurings is information, where the other is misinformation.  As light structure, they are the same.  At most, calling one "information" and the other "misinformation" is just to rename the one light structure as coming from the normal box, where the other light structure as coming from the exploding box.

Gibson and the Learning of Affordances

Let me add a comment on this passage:

"The central question for the theory of affordances is not whether they exist and are real but whether information is available in ambient light for perceiving them. The skeptic may now be convinced that there is information in light for some properties of a surface but not for such a property as being good to eat. The taste of a thing, he will say, is not specified by light; you can see its form and color and texture but not its palatability; you have to taste it for that."
Gibson, 1979, p.140-141

Andrew, Gary, and Gennady have each proposed that Gibson could handle exploding box cases by appeal to learning.  (Now, this won't work, since your learning is not going to change the ability of a typical affordance to structure light.  The problem is that surfaces are on the outside of objects, but what makes for the typical affordance is on the inside of the object, so the light can reach to affordance to be structured by it.)   And, they are right that Gibson does mention learning about affordances. But, notice that, following this passage, Gibson might well just admit that the palatability of a thing is not specified by light and that you have to learn whether an object affords palatability by tasting it, then .....?  Instead, he presses on with the view that higher-order invariants in light are going to save the day.  So, in what follows in this passage, he is more willing to stay the course in saying that affordances are specified by light than have been Andrew, Gary and Gennady.  But, then again, Gibson apparently didn't consider anything exactly like the exploding box protocol.  So, it seems to me that Gibson is somewhat equivocal regarding how he might handle such cases. 

Gibson, Exploding Boxes, Invariants, and Higher-Order Invariants

So, Gennady believes that a solution to the exploding box type cases can be found in the following.  The skeptic, which would be me, puts the view on the table in the first half of this first paragraph.  Gibson's reply follows.

Gibson, 1979, p.140-141
"The central question for the theory of affordances is not whether thy exist and are real but whether information is available in ambient light for perceiving them. The skeptic may now be convinced that there is information in light for some properties of a surface but not for such a property as being good to eat. The taste of a thing, he will say, is not specified by light; you can see its form and color and texture but not its palatability; you have to taste it for that. The skeptic understands the stimulus variables that specify the dimensions of visual sensation; he knows from psychophysics that brightness corresponds to the intensity and color to wavelength of light, He may concede the invariants of structured stimulation that specify surfaces and how they are laid out and what they are made of. But he may boggle at invariant combinations of invariants that specify the affordances of the environment for the observer. The skeptic familiar with the experimental control of stimulus variables has enough trouble understanding invariant variables I have been proposing without being asked to accept invariants of invariants.

Nevertheless, a unique combination of invariants, a compound invariant, is just another invariant. It is a unit, and the components do not have to be combined or associated. Only if percepts were combinations of sensations would they have to be associated. Even in the classical terminology, it could be argued that when a number of stimuli are completely covariant, when they always go together, they constitute a single "stimulus." If the visual system is capable of extracting invariants from a changing optic array, there is no reason why it should not extract invariants that seem to us highly complex.

The trouble with the assumption that high-order optical invariants specify high-order affordances is that experiments, accustomed to working in the laboratory with low-order stimulus variables, cannot think of a way to measure them. How can they hope to isolate and control an invariant of optical structure so as to apply it to an observer if they cannot quantify it? The answer comes in two parts, I think. First, they should not hope to apply an invariant to an observer, only to make it available, for it is not a stimulus. And, second, they do not have to quantify the invariant, to apply numbers to it, but only to give it an exact mathematical description so that other experimenters can make it available to their observers. The virtue of psychophysical experiment is simply that it is disciplined, not that it related the psychical to the physical by a metric formula."

Ok.  So, Gennady thinks the invariants and higher-order invariants story is going to solve problem with the exploding box type cases.  But, grant Gennady and Gibson their invariants and higher-order invariants in light.  The problem remains: the physical surfaces on the outside of the boxes are what structure the light into invariants and higher-order invariants, but the inside of the boxes are what constitute or anchor affordances, such as for pick-up-ability, stand-on-ability, climb-on-ability.  So, both boxes are going to have the same invariants in the light and the same higher-order invariants in the light, so the visual perceivers will have the same visual perceptions.  The visual perceiver does not visually perceive the pick-up-ability of the exploding box, and since this visual perception is the same as visual perception of the normal box, the visual perceiver does not visually perceive the pick-up-ability of the normal box either.

The basic problem remains.  Simplifying: What structures light is typically on the outside of objects; what constitutes affordances are typically on the inside of objects.

Future Posts 2/8/2011

So, over the next few days I'll be moving on a bit in my posts on Gibson, 1979, p. 127.  (I think I've been beating a dead horse, but Andrew seems to think the horse might be good for another quarter mile.)  A number of replies have cropped up in comments and I would like to bring them to the top in separate posts of their own to try to make clear how I do not think they will help.  These include appeals to other sense modalities, to learning, and maybe "looking X-able".  But, I'll be drawing more on Gibson, 1979, Chapter 8, for anyone who is reading along. (Thanks to Gennady for bringing this additional material to the front.)

Is this stand-on-able?1

 

Does the surface of this stool structure light in such a way as to enable a human to visually perceive that this is stand-on-able?

Chemero and the Exploding Boxes

In comments, Andrew has asked whether Chemero's, 2009, approach to information helps with the exploding box type cases.  I have not read the whole of the relevant chapters yet (Chapters 6 and 7, I think), but I think the answer is now.  Moreover, the problem rears its head right about here:

Imagine that there is a beer can on a table in a room that is brightly lit from an overhead source. Light from the source will reflect off the beer can (some directly from the overhead source, some that has already been reflected off other surfaces in the room). At any point in the room to which there is an uninterrupted path from the beer can, there will be light that has reflected off the beer can. Because of the natural laws governing the reflection of light off surfaces of particular textures, colors, and chemical makeup, the light at any such point will be structured in a very particular way by its having reflected off the beer can. In situation s1, the light at point p has structure a of type A. Given the laws just mentioned, there is a constraint connecting the situations with light-structure type A to the beer-can-present situations of type B. So the light structure at point p contains information about token beer-can-presence b (of type B). Notice too that, because of conventional constraints governing the relationship between cans and their contents, beer-can-presence b being of type B carries information about beer-presence c of type C. Furthermore, the light at some point in the room from which the beer can is visible will contain information about the beer can's affordances. Take some point p, which is at my eye height. The light structure available at this point will contain not just information about the beer can and the beer, but also about the distance the point is from the ground, the relationship between that distance and the distance the beer can is from the ground, and hence the reach ability of the beer can and drinkability of the beer for a person with eyes at that height. (Chemero, 2009, pp. 118-9)

Ok.  So, the stuff up until "Notice too that ..." is essentially the Gibsonian line (of Gibson, 1979, p.127) about surfaces structuring light.  That sound right.  The trick, then, is to somehow connect the structuring of light by surfaces to affordances.  Gibson, 1979, p. 127, tried to make the connection by way of the hypothesis that the composition and layout of surfaces constitutes affordances.  Chemero has a different idea: There are constraints between surfaces and their innards.  In the case of beer cans, society puts beer in beer cans.  That's the constraint.  From there, Chemero glides willy-nilly (i.e. without telling us how) to having constraints go all the way to drinkability.

But, this is not going to work.  Take two beer cans that are physically identical on the outside.  Have one with beer and the other with something non-potable, say, bleach.  Subjects will, presumably, have the same visual perceptions of the two cans, but the two cans afford different things, so visual perception is not of affordances.  I take it as evident how to run this with the exploding boxes, piles of white stuff, panes of glass, etc.

This goes back to the cartoonish formulation of the problems.  Visual perception is typically based on outers; affordances are typically based on innards.

Chemero could rightly point out that in this imagined scenario, we do not have the requisite conventions regarding the contents of beer cans.  Correct, but we still have perception, right?  Which suggests that social conventions regarding the physical configurations of things do not have that much to do with perception.

Maybe there is some trick Chemero has up his sleeve later, but we shall see ...

Is this Walk-on-able? 2

Does the glass floor structure light in such a way as to enable a human to visually perceive stand-on-ability?

Charles wondered, at one point, whether my exploding box example was just some philosophical exotica, like imagining a wizard, but as I said earlier, the point is completely pedestrian.  The basic point can be transferred to plenty of other examples.

I guess it's unfortunate that the EPists have been too busy to test one of the fundamental assumptions of Gibson's theory, namely, whether the composition and layout of surfaces constitute affordances, or the TSRM assumption that anchoring properties structure light.

Is this Walk-on-able? 1

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?

Is this edible? 4

Do the surfaces here structure light in such as way as to specify whether this is edible for humans?

Is this edible? 3

Do the surfaces of these pellets really structure light in such a way as to specify whether they are edible for humans?

Is this edible? 2

Does the surface of this statue really structure light in such a way as to specify whether it is edible for humans?

The affordance for alight-on-ability

So, take to boxes 3' x 3' x 3' in size. They are physically identical on the outside, but one is rigged with a motion sensitive device so that it will explode if you move near it.

I say they are visually perceived to be the same, but that they afford different things (one affords alight-on-ability; the other does not). So, one does not perceive alight-on-ability.  (Cf. TSRM, 1981, p. 261 for the example of alight-on-overability).

The Perception of Leap-over-ability

So, take to boxes 3' x 3' x 3' in size. They are physically identical on the outside, but one is rigged with a motion sensitive device so that it will explode if you move near it.

I say they are visually perceived to be the same, but that they afford different things (one affords leap-overability; the other does not). So, one does not perceive leap-over-ability.  (Cf. TSRM, 1981, p. 261 for the example of leap-overability).

The perception of stand-on-ability

So, take to boxes 3' x 3' x 3' in size. They are physically identical on the outside, but one is rigged with a touch sensitive device so that it will explode if you stand on it.

I say they are visually perceived to be the same, but that they afford different things (one affords stand-on-ability; the other does not). So, one does not perceive stand-on-ability.

Maybe some surfaces can constitute some affordances

Perhaps the composition and layout of surfaces constitutes what they afford.  (Gibson, 1979, p. 127).

If see-ability were an affordance, then maybe it could be an affordance that is constituted by the composition and layout of surfaces.

If ability-to-be-an-occluder were an affordance, then maybe it could be an affordance that is constituted by the composition and layout of surfaces.

I don't know that these are the kinds of affordances that EPists have envisioned.  Maybe not.  But, they look to be exceptional cases.  The point of the exploding boxes cases is to get a clear simple case to use as a beach head, then press on from there.  I don't think one necessarily has to eliminate all cases of the composition and layout of surfaces constituting affordances in order to challenge the significance of the view.

S does not visually perceive pick-up-ability in the normal box

Here's the argument.

Take two ring boxes that are physically identical on the outside (in their surfaces, if you will), but one is normal where the other is rigged with a touch-sensitive explosive mechanism.  If you touch the box, it will explode.  Give them identical conditions of lighting, temperature, etc.  That's just my stipulation.

Suppose we agree that if you can't touch the box, then you can't pick it up.  (Some room to argue there, perhaps.)

Suppose we further agree that we do not visually perceive pick-up-ability in the exploding box.  It doesn't have the property of pick-up-ability, so you cannot (factively) visually perceive it.

(*) Since they are physically identical on the outside (in their surfaces, if you will) and in their background lighting conditions, one will have identical visual perceptions when viewing them.  

(*) is not a stipulation, but an empirical hypothesis.  So there is perhaps some room to challenge it.

The stipulation plus (*), however, appear to suffice for a very simple and kind of radical objection to EP.

If subject S does not visually perceive pick-up-ability in the exploding box, then since what S visually perceives of the exploding one, S perceives of the normal one, S does not visually perceive pick-up-ability in the normal box.

So, S does not visually perceive pick-up-ability in the normal box.

Gibson: Are Affordances Constituted by the Composition and Layout of Surfaces?

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).

So, here is a crucial juncture for Gibson.  He's got all this apparatus about surfaces.  (Sentence 1)  He's got all this talk about affordances.  (Sentence 2) How do they fit together?  (Sentence 3)  Maybe information from surfaces could give you information about affordance? (Sentence 4).  But, how could that work?  Possible answer: The composition and layout of surfaces constitutes what they afford.  (Sentence 5.)

But, the problem is that the composition and layout of surfaces does not constitute what they afford.

The pick-up-ability of a box is not constituted by its surface; it's constituted by what's inside, namely, not having a touch-sensitive explosive device inside.

The walk-on-ability of pond ice is not constituted by its surface; it's constituted by its whole thickness.

The sit-on-ability of a chair is not constituted by its surface; it's constituted by the weight bearing properties of the whole of the components.

Gibson, 1979, Chapter 8

Andrew just suggested that the exploding box example is not a problem for EP.  But, it's the kind of case that appears to be relevant in evaluating empirical claims suggested in the following:

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?  (Gibson, 1979, p. 127).

So, consider the last question: "If there information in light for the perception of surfaces, is there information for the perception of what they afford?"

Now, there is, to my mind, an ambiguity in this.  Notice that, strictly speaking, Gibson is writing about surfaces, not objects.  To see this, replace the pronoun with its antecedent:

(A) If there information in light for the perception of surfaces, is there information for the perception of what surfaces afford?

Contrast that with the question: 

(B) If there information in light for the perception of surfaces of an object, is there information for the perception of what the object affords?

Now, (A) is a little odd, since it is perhaps not the surface of the fish, say, that affords edibility, but the "meat" of the fish that affords edibility.  Or, to use a TSRM example, it is not the surface of a thing that affords potability.


Now, contrast these questions with some more restrictive questions:

(A') If there information in light for the perception of surfaces, is there information for the perception of what surfaces afford prehension?

Contrast that with the question: 

(B') If there information in light for the perception of surfaces of an object, is there information for the perception of what the object affords prehension?

Maybe this too reads a bit awkwardly, but one gets the idea (I hope) that it is not the information for all affordances that is provided by information in light for the perception of surfaces; instead, it is only the information for prehension affordances that is provided by information in the light for perception of surfaces.

Finally, there are questions about even weaker matters, like the one's Noë hints at,

(A'') If there information in light for the perception of surfaces, is there information for the perception of some of the properties that surfaces afford?

Contrast that with the question: 

(B'') If there information in light for the perception of surfaces of an object, is there information for the perception of some of the properties that the object affords prehension?

Noë on Gibson on Affordances

Here is a kind of interesting passage from Noe's paper:

On a familiar reading of Gibson (1979), he is said to have held something like this. For example, Campbell (2002) characterizes Gibson as follows:

... suppose, for example, that an unfamiliar piece of apparatus appears on a workbench. I have no idea what this thing is for. I don't know if I can touch it - maybe I will be electrocuted, or the thing will blind me, if I do that. Or maybe it is simply the latest kind of television, or a paper weight. So I don't see it as affording anything in particular. In that case, by Gibson's theory, the thing should be simply invisible; I should be able to see it only when I am told what it is for. But that is not a persuasive conclusion; it seems perfectly obvious that we can see things without knowing what they can be used for.
(Campbell, 2002, p.143)

As I read Gibson he is not committed to such a conclusion, for it is not Gibson's view that we only see affordances, or that we can only see objects in so far as we can see their affordances. Gibson's point comes earlier: that we can see affordances. The significance of his thought is this: for Gibson, perceptual consciousness is not confined to so-called categorical properties of things, such as shape say, or size, or qualities like colour. Gibson is advancing 'the radical hypothesis' that 'the "values", and "meanings" of things in the environment can be perceived directly' (Gibson, 1979, p.127).  (Noë, 2010, p. 247).

Now, I had always thought that Gibson's view is that one always perceives affordances.  I'm not entirely sure why, but I thought that perception was always supposed to work something like this: Affordances structure light (for example) and humans pick up the information in the light.  Simple.

I wonder how many people read Gibson as Noë does.  Comments welcome.  Comments with references to Gibsonian pronouncements even more welcome.

But, suppose that Noë is right.  Is there some place where Gibson spells out when one perceives (or can perceive) affordances and when not.  In other words, when do we get affordance perception and when do we not?