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.