Thursday, March 05, 2009

Illusions and Practical Competence

Eric Schwitzgebel has a fascinating post on illusions, and whether they still count as such when the viewer is so familiar with them as to no longer be disposed towards misjudgment:
If one knows enough about the world, one should know that an oar partly submerged in water (seen from a particular viewing angle) should look bent just like that. If it looked straight, I suppose, a longtime oarsman or a person very familiar with the laws of refraction might think the oar looked strange, might even think that it looked like an oar that is actually bent (bent in such a way as to exactly compensate for the bend a straight oar would seem to have at that angle)...

So is the skilled oarsman experiencing a visual illusion as he looks at the oar? If we say no, then I'm worried we're off onto a slippery slope to entirely denying the possibility of illusions that are known to be such.

Note, though, that's there's a fair gap between mere propositional knowledge and the kind of internalized know-how or "fluency" possessed by the skilled oarsman. I am still very much 'taken in' by the Muller-Lyer illusion, despite - intellectually - 'knowing' that it is an illusion. For it to cease to count as an illusion to me, I would need to internalize this knowledge in such a way as to render me fluent in interacting with Muller-Lyer lines. (Were I to come across a worldly instance, I should automatically respond in ways appropriate to the lines being of equal length; just as the skilled oarsman automatically responds appropriately to the shape of his oar in the water.)

djc adds:
Another nice case is that of mirrors. Does looking at a mirror create an illusion that twin-you is in front of you? When one doesn't know it's a mirror, the "yes" answer seems plausible, but this answer rings less true for the familiar case when one knows it's a mirror. But if one says "no" in this case, then the question is whether there's a principled distinction between this case and the bent stick case, or any other case of a "known illusion".

I suppose that for there to be a principled distinction, one will have to make the case that in some cases (e.g. the mirror case), knowledge of the relevant effect penetrates the experience and changes its content, while in other cases (e.g. the stick case) knowledge does not penetrate the experience in this way. Perhaps there is some intuitive plausibility to the claim that the relevant spatial phenomenology is changed by mirror knowledge in a way that it's not changed by bent-stick knowledge. But it's not clear what the source of this difference is.

Could practical competence vs. merely intellectual knowledge ground this difference? (Imagine someone who has just learned what a mirror is, but who is not yet sufficiently practiced to be competent at using them. It seems plausible that the mirror could still create a sense of 'illusion' for them, even though they know full well - intellectually, at least - what is going on.)

[Related posts: What is illusion?]


  1. Hi Richard,

    An interesting way to handle these kinds of cases, and this sounds very much like what you are saying, is a kind of Sellars/Churchland line that, like your suggestion, emphasizes automaticity. If someone is trained to automatically (that is, without intervening inference) apply the concept of straightness to the oar half out the water, then they count as perceiving the oar as being straight (as opposed to inferring that the oar is straight from a crooked sense datum, or whatever).

  2. Hi Pete, I wouldn't want to go so far as to deny that we can make (subconscious) inferences automatically. As my linked older post points out, we don't want to say that a Fake Barn facade is an illusion. Our perception itself is accurate enough in such a case; it's instead the automatic inference we draw that's faulty.

    So perhaps the automaticity rule only applies with limited scope, e.g. to basic perceptual features -- shape, size, etc. -- but not to richer concepts like 'being a barn'. (Is there a principled line to draw here?)

  3. Interesting suggestion, Richard. As your reply to Pete suggests, there's at least a little trouble (or complication) brewing.

    One might think that facts about phenomenology (e.g., the phenomenology of illusion) and facts about dispositions to behave are rather different, so that an analysis of the former in terms of the latter will never quite do. But of course that's a controversial philosophical position!

  4. Thanks, Eric! Your caution against analysing phenomenology in terms of behavioural dispositions is well-taken. I think the link is merely contingent -- so while my proposal is (hopefully) extensionally adequate for actual human beings, there's definitely more that needs to be said. In particular, I assume that there's some further story to be given about how properly internalized knowledge "penetrates the experience and changes its content" (to borrow djc's phrase).

    (Perhaps there's also more to internalized knowledge than just the behavioural dispositions. Appropriate automatic behaviour may be a symptom of such knowledge, rather than constitutive of it. I'm very unsure about all this, though.)


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