Over at Brainhammer, Pete Mandick set out the
following problems for info-semantics:
If it's determinate specifications you are worried about, it's worth
keeping in mind that causal/informational stories haven't been without
their own problems. Regarding specificity, there are all sorts of
problems concerning where in the causal chain to locate the content
(e.g. proximal or distal causes). Also, there are serious problems
about how to represent things that couldn't enter into causal chains
with our minds because, eg., they are outside of our light-cone, or
they don't exist, or are too abstract.
Pete points out two serious problems with informational semantics (I'm using information rather than cause):
1) Where in the information chain do we locate the content. For instance, why say that LGN represents what is happening in the world rather than in the retina?
2) How would you represent things that don't exist, such as unicorns? No neuronal state has every carried the information that a unicorn is present. Note I'm presently not even going to try to answer the problem of knowledge of abstracta such as 'Two is even.'
3) Pete could have added the problem of individuating coextensional contents such as 'square' and 'four-sided equiangular polygon.'
In what follows, I'll outline what Dretske says in response to the first challenge. He deals with the second and third on pages 229ff and 215ff, respectively, of Knowledge and the Flow of Information. Perhaps I'll discuss them in a later post.
Note I'm not sure Dretske is right, but at the very least he is being reasonable. I hope to impress that Dretske is simply a bad ass, adeptly presaging many potential problems with his entire framework. Indeed, I have not run into a single objection to Dretske's work that he hasn't forcefully expressed and dealt with (tried, at least) in his own writings. Since it is already lengthy, I am saving my own criticisms of his view for the comments: I'm just trying to charitably expound his view here (I can't beat his felicity of expression without a ton of work, so I'm being lazy and relying heavily on quotes).
On to the problem of the information chain.
There are really two problems here, both nasty for Dretske.
I. The problem of hearing buttonsFor one, you could end up going
too far out in the causal chain that generates a representation. E.g., consider the chain of someone pushing a button that closes a circuit which causes a doorbell to ring. From pages 156 ff, "Why does he not hear the button being depressed? Why does he not hear the membrane vibrating in his ear? ... What makes the bell so special that we designate
it as the thing heard?...What is the information-theoretical basis for this distinction? Why is one the object and not the other when the auditory experience (by hypothesis) carries specific information about
both?"
Here he invokes a technical term, the notion of a primary representation as opposed to a secondary representation. Basically, the brain represents the bell as a primary representation and the button as a secondary representation, and it is only the former which we explicitly represent. First I'll give the text where he fleshes this out in the doorbell example, and then give the general definition of primary and secondary representation.
"Our auditory experience represents [carries information about] the bell ringing and it represents the button's being depressed. But only the former is given a primary representation because the information the experience carries about the depression of the button depends on on the informational link between the button and the bell while its representation of the bell's ringing does not depend on this relationship. If we short-circuit the doorbell wires (causing the bell to ring periodically when no one is at the door), the informational tie between the bell and the button ins broken. When this tie is severed, the auditory experience continues to represent (carry information about) the ringing bell, but it no longer carries information about the depression of the button.
"If, contrary to hypothesis, the auditory experience
continued to represent the button's being depressed...even when its informational link with the ringing bell was broken,
then we could speak about the button's being depressed as itselve receiving primary representation...But in precisely this situation we would speak of our ability to
hear the button's being depressed...If the button was very rusty, for example, and squeaked loudly whenever it was depressed, we might be able to hear the button being depressed whether or not it was connected to the bell. The explanation for this fact is that, in these altered circumstances, the button's being depressed is no longer being given a
secondary representation in terms of the bell's ringing" (160-1).
Note his technical definition of primary representation is roughly 'State S gives primary representation to property B (and secondary representation to property P) iff S's representation of something being P depends on the informational relationship between B and P but its representation of B does
not depend on the informational relationship between B and P' (p. 160). Here S is the internal representational state, B is the bell, and P is the button push.
II. The problem of hearing eardrumsThe second problem is, why should we say the person hears the doorbell and not his eardrum vibrating? That is, you could end up pushing the representational contents
too close to the subject, so you end up representing transduction mechanisms such as retinal activity or ear drum vibrations rather than things out in the world. Dretske says (p. 162) "The distinction between primary and secondary representations serves to explain why we hear the doorbell ringing and not the door button being depressed. But it does
not help explain why we hear the doorbell ringing and not, say the vibration of the membranes in our ear. Isn't the ringing of the bell given secondary representation relative to the behavior of the membranes in our ear?"
Dretske has two potential solutions to this problem. The first (p. 163ff) averts to perceptual
constancy mechanisms. E.g., our visual experience of an object remains quite similar even through drastic changes in peripheral mechanisms. "Size, shape, and color constancy testify to the fact that it is the
properties of objects and not (say) the properties of the retinal stimulation (or the firing of neural cells), that is represented by our visual experience under normal viewing conditions. The visual experience that constitutes our sensory encoding of information about ordinary physical objects can, and generally
does, remain unchanged in response to quite different proximal stimulation...Our sensory experience is sensitive to (hence carries information about),
not the behavior of our receptors or neural pathways, but the behavior of more distant elements in the causal chain."
His second solution (p. 187 ff) is that a true semantic structure is mute about its own causal origins. Again, I'll quoting Dretske (from p. 188): "A semantic structure's insensitivity to its particular causal origin, its muteness about the particular manner in which the information (constituting its semantic content) arrived, is merely a reflection of an important fact about beliefs. Our belief states do not themselves testify to their causal origin. The fact that someone
believes that Elmer died tells us nothing about how he came to believe this, what caused him to believe it. He may have read it in the newspaper or someone may have told him; he may have seen Elmer die, or he may have discovered this in some more indirect way...It carries this information, yes, but it says nothing about how this information arrived...
"This plasticity in extracting information from a variety of different signals, a plasticity that accounts for a system's capacity for generating internal states having information about a distance source as their semantic content, is a plasticity that most information processing systems lack. [In a voltmeter] the only way information about voltage differences can reach the pointer is via current flow, induced magnetic field, consequent torque on the armature,...Since, given the construction of the instrument, this is the
only way the pointer's position can register the voltage, the pointer's position carries information about all these intermediate events...This is why voltmeters do not believe anything." [Phew]
Note also that Dretske discusses this issue extensively in his beautiful article
Misrepresentation.
Three points:
