Failing to See the Illusion

C. Projection of Experts’ Expectations on their own Experience

A third possibility is perhaps ungenerous to the illusion-creators and the judges. Yet, given the hypothesis on which it’s based, it seems to be a possibility. It’s this: the judges, creators etc. are all experts and aware of the what might be called “(visual-experience = hypothesis)+(the-hypothesis-is-about-depth). Their tacit acceptance of this theory affects their judgements about what they see. So,

(a) Their visual experience is altered by their expectations (a variant of the prediction model of perception — e.g. a talk last February by Lange). They see the difference because their beliefs cognitively penetrate (Susanna Siegel paper) their perception. By my own hypothesis, my beliefs also penetrate my perception — but I don’t know what those beliefs are; they aren’t now that I will see 3D depth.


(b) Their interpretation of visual experience is altered by their expectations

Both look to be just examples of the Gestalt/Gregory idea of perception as hypothesis. It also explains perhaps why I don’t see what I do. I don’t have those expectations about what I see.

There is perhaps one serious problem with this. If I understand the hypothesis right, it is not supposed to be that perception is susceptible to recent or higher-order beliefs. The beliefs that penetrate perception are evolved over millions of years or developed in childhood (for example, with respect to the Muller-Lyer illusion, see McCauley and Heinrich 2006). That I have a quite sophisticated view about perception should not alter what I seem to see when I am looking at something.

Then, again, maybe what I am saying here is a counter-example to that claim. The claim here is that this is an example of a case where experts about illusion generate illusions non-experts can’t experience. This might be just the kind of example you’d expect if you thought knowledge or thought alters experience.

And again, this might have a precedent. In his book ‘Aspects of Motion Perception‘, the perceptual psychologist P.A. Kolers (not the Gestalt psychologist Wolfgang Kohler) studied in depth the phenomenon called apparent motion — commonly, the appearance of one thing moving where there is actually only a sequence of unconnected stimuli — and so no motion as such (the phi phenomenon is an example).

One claim he made there was that the apparent motion effect grows stronger through practice and repetition — people see illusory motion after such practice/repetition in cases where the unpracticed do not (p.158). It’s a different kind of idea of expertise — more habituation, but it involves adults’ perceptions changing ‘live’, as it were, in their responses to potential illusions.

As a final anecdotal example — which will convince no-one needing convincing — I advance this: until I started considering it in University, I don’t remember ever seeing the difference between the lines in the Muller-Lyer illusion. I think I had to be told what was going on before I started seeing it. Then again, perhaps I am having a false memory of that (thus further proving the hypothesis that hypthoses alter experience).

Anyway, for now, I prefer ‘A’.


1. At the same time, though, I never checked with the opthamologist and have never followed up on it. So it might all be just a lot of self-indulgent guff.

Also, I could still have a little 3D vision anyhow; I remember reading (though I cannot find a source now) that each eye alone has some degree of 3D vision. A dominating eye should still provide its own stereopsis (albeit, the name would be misleading).

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