Thursday, March 2, 2017

Probabilistic perception

We could imagine critters whose perceptual system works as follows: When they have an object in their visual field, instead of the perceptual system delivering the presence of a dog, it delivers something like:

  • dog:0.93, coyote:0.03, wolf:0.03, deer:0.01.

There are probably many interesting questions to ask about critters with a perceptual system like that. But I want to briefly muse about three.

Question 1: Can we redescribe the perceptual system of these critters so that at base what we have are just attitudes to propositions or properties pairs or something like that?

Answer: I am not sure. Some options fail. For instance, while it may be true that the critter in my example is having a disjunctive perception of a dog-or-coyote-or-wolf, that doesn’t capture all the information in its perceptual system—it doesn’t capture the much greater probability of its being a dog.

Alternately, one could say that the critter has four perceptions of different strengths: a 0.93 strength perception as of a dog, a 0.03 strength perception as of a coyote, a 0.03 strength perception as of a wolf and a 0.01 strength perception as of a deer. But that doesn’t quite capture what’s going on, at least not if we read the story as I intended it. The critter takes dog, coyote, wolf and deer to be alternative hypotheses for what is in front of it, not to be four different perceptions. The story that breaks up the perception into four perceptions of different strengths fails to distinguish the story I intend from a story where the animal might be all four (it’s only a posteriori that we know there are no dog-coyote-wolf-deer).

Maybe we could say that the critter’s perceptual system also delivers something more complicated:

  • only-dog:0.93, only-coyote:0.03, only-wolf:0.03, only-deer:0.01.

That will get out of the alternativeness worry, but I am sceptical that it needs to be like that. One could just see the four options, and not see that the probabilities involved force them to be exclusive (because the probabilities add up to one). This is even more plausible if the probabilities are qualitative or interval-based.

Nor will it do to say that one perceives that there is a 0.93 probability of a dog, a 0.03 probability of a coyote, and so on. For these probabilities are not objective facts out there. They are, I suppose, measures of what credence the critter should have in each hypothesis if there is no further data available. We need not suppose that the critter has the degree of self-reflectiveness that would be needed to perceive these measures of hypothetical credence as such.

So maybe a reduction to more familiar perception stories is possible, but I think there is some reason to be sceptical.

Question 2: What is it for this perceptual state to be veridical?

Answer: A necessary condition, of course, would have to be that what is present is a dog, coyote, wolf or deer. But there is room for much Gettiering. Maybe it’s a wolf dressed up as a sheep dressed up as a wolf. Then the perception isn’t in the right way, and we don’t have veridicality. But what if it’s a dog that recently went to the pet salon and was made up to look more wolf-like? Then maybe it’s veridical. Maybe. I just don’t know.

I have a suspicion that once we have such probabilistic deliverances of perception, the in-the-right-way problem of characterizing veridicality not only becomes epistemically intractable—it may already be that in standard theories of perception—but the whole concept of veridicality, apart from the necessary condition that one of the alternative hypotheses be true, may break down.

Question 3: Are we always such critters? We could, after all, take the ordinary perception of a dog to be just a limiting case like “dog:0.999999, something weird:0.000001” or even “dog:1”. Should we do that in every case?

Answer: Phenomenologically, the answer seems negative. But phenomenology can mislead about such things. But as long as it’s a live hypothesis that we might be such critters, we may need to be cautious about claims like that perception is a propositional attitude (see Question 1) or that there is a viable concept of veridicality (see Question 2).

And the apparent possibility of critters whose perception always works like this should make us cautious as to the kinds of claims we make in epistemology.

1 comment:

Heath White said...

I think we are such critters. If you are out west, seeing a vaguely canine shape in the far distance, dog and wolf and coyote are all live possibilities.

Avoiding the Myth of the Given, I think we should describe it like this. There is something canine in the visual field, but this is a sensation not a belief or propositional attitude. This sensation CAUSES let's say three propositional attitudes, viz. "It's a dog", "It's a wolf", "It's a coyote." Attached to each of these attitudes is a credence, say 0.9, 0.05, 0.05.

The attitudes are veridical when their content is true. What it is for their credences to be correct is a separate question and I don't know the answer, unless it is very simple: the fact of having the sensation is evidence for each of three hypotheses and we handle that piece of evidence like any other.