Self-Blindness?
If introspection is essentially a matter of perceiving one's own mind, as philosophers like John Locke and David Armstrong have suggested, then just as one might lose an organ of outer perception, rendering one blind to events in that modality, so also, presumably, could one lose an organ of inner perception, leaving one either totally introspectively blind or blind to some subclass of one's own mental states, such as one's beliefs or one's pains.
Is such self-blindness possible? There are, as far as I can tell, no clear clinical cases -- no cases of people who feel pain but consistently have no introspective awareness of those pains, no cases of people who can tell what they believe only by noticing how they behave. (I'm excluding cases where the being lacks the concept of pain or belief and so can't ascribe those states at all; and with apologies to Nichols and Stich on schizophrenia). Sydney Shoemaker suggests that the absence of such cases flows from a deep conceptual truth: There's a fundamental connection between believing and knowing what you believe, between feeling pain and knowing you're in pain, that there isn't between being facing a red thing and knowing you're facing a red thing -- and thus in this respect introspection differs importantly from sensory perception.
Since I'm generally a pessimist about the accuracy of introspective reports, my first inclination is to reject Shoemaker's view and allow the possibility of self-blindness. But then why do there seem to be no clear cases of self-blindness? I suspect that in this matter the cases of pain and belief are different.
Consider pain first. Possibility one: The imagined self-blind person has both the phenomenology of pain and typical pain behavior (such as avoidance of painful stimuli), maybe even saying "ow!" If so, on the basis of this behavior, she could determine (as well as anyone else could, from the outside) that she was sometimes in pain; but she would have no direct, introspective knowledge of that pain. Contra Shoemaker, this seems to me not inconceivable. However, it also seems very likely that a real, plastic neural system would detect regularities in the neural outputs generating pain behavior and respond by creating shortcuts to judgments of, or representations of, pain -- shortcuts not requiring sensory detection of actual outward behavior. For example, the neural system could notice the motor impulse to say "ow!" and base a pain-judgment on that impulse (perhaps even if the actual outward behavior is suppressed). This then, might start to look like (might even actually become?) "introspection" of the pain.
Alternatively, the self-blind person might show no pain behavior whatsoever. Then the person would behave identically to someone with total pain insensitivity (and cases of total pain insensitivity do exist). But now we're faced with the question: Do people normally classified as utterly incapable of feeling pain really feel no pain, or do they have painful phenomenology somewhere with no means to detect it and no way to act on it? The latter possibility seems extravagant to me but not conceptually impossible. And maybe even a fuller understanding of the neuropsychology of pain and pain insensitivity might help us decide whether there are some actual cases of the latter.
Regarding belief, I'm more in sympathy with Shoemaker. My own view is that to believe something is just a matter of being prone to act and react in ways appropriate to, or that we are apt to associate with, having the belief in question (taking other mental states and excusing conditions into account). Among the actions and reactions appropriate to belief is self-ascription of the belief in question, self-ascription that doesn't rely on the observation of one's own behavior. Someone who had the concept of belief but utterly lacked direct self-ascriptive capacity would be in some way defective not just as a perceiver of her beliefs but as a believer.
(Thanks to Amy Kind and Charles Siewert whose excellent articles criticizing Shoemaker on self-blindness prompted this post.)