Perceptual and Rational Bias

Suppose I learn that most (but not all) people have a condition which leads them to misperceive purple line segments as only being about half as long as they really are. Further suppose I have no special evidence regarding whether I myself am one of the people with this odd condition. Now I see a purple line, which seems to me about an inch long. How long should I believe it is? (Here I use 'belief' to simply indicate the bulk of one's credence. It is what one would choose if forced to bet one way or the other.) Two inches, presumably.

Next, suppose I learn that most academics in my vicinity have been exposed to a drug that leads them to make inverted evaluations without realizing it: they're inclined to give A grades to C-meriting papers, and vice versa. As before, I have no special grounds for expecting myself to be free of this condition. Now I read a paper by Joe Shmoe that seems hopelessly incoherent and deserving of a C. What grade should I give it? An A?

Erica Roedder proposes an analogy roughly along these lines, but I think the two cases are importantly different. In the first case -- what I'll call 'perceptual bias' -- the only reason for believing that the line is an inch long is the phenomenology of it seeming so. You only have access to the phenomenal 'output', and not to any of the raw data or 'inputs' that form the bases of this judgment. So once you learn that the phenomenology is actually evidence of something else -- namely, the line being twice that length -- that settles the matter. There is no further evidence in play.

However, in case of 'rational bias' -- cases like the second where we make bad inferences or otherwise misinterpret some independently available evidence -- we have more to go on. In addition to the output of our initial judgment, there is also the raw data of the paper itself. So presumably the epistemic fact of what we should believe depends on all this evidence, and not only the higher-order evidence provided by our initial judgment. My initial judgment of badness provides some evidence (due to the known likelihood of bias) that the paper is actually good. But that doesn't settle the matter, for surely the details of the paper itself are also relevant to what grade I ought to give it!

Let's consider the two possibilities in turn. Either I'm biased and the paper is actually good, or I'm unbiased and the paper is truly bad. If the paper is actually good, then both the first-order evidence provided by the paper and the higher-order evidence provided by my initial judgment agree: I should conclude that the paper is good. Simple.

Now for the more interesting possibility: suppose the paper truly is bad. It's still the case that my initial judgment of badness provides some higher-order evidence that the paper is actually good. But there is also the first-order evidence of the incoherent paper itself, which pretty strongly establishes its low quality. I have access not only to my initial judgment, but also to the paper itself and the fact that it reads as follows: (*insert copy of incoherent paper here*). It seems entirely possible that this latter evidence could outweigh the former, in which case I really should conclude that the paper is bad, and give it a C.

In summary: we should correct for the likelihood of perceptual bias, even if it turns out we weren't biased. This is because we have no other evidence to go on in such a case. But cases of rational bias are different, and the appropriate response is contingent on further details. If we are biased, then of course we should correct for it -- that's uncontroversial. But the actually non-biased person arguably should not recalibrate their judgments, or at least not to the same degree. This is not just because they happen to be non-biased (they obviously have no access to this fact), but because of other facts they do have access to, namely the first order evidence.