I am currently a Mellon Postdoctoral Fellow at Oxford. Most of my research is in philosophy of mind, cognitive science, and psychiatry (although I also have a strong interest in Hume). Among other things, I'm currently thinking a lot about delusions.
It seems to me that most current philosophical work on delusions is heavily focused on two issues. First, as we can see from this blog, there is a lively and engaging debate about whether delusions are doxastic states or some other kind of mental state.
Secondly, there are discussions about the best framework or model to adopt for explaining delusions - for example, whether we should adopt a one-factor or two-factor theory or whether some kind of Bayesian model could be developed to explain the onset of delusion. Although I think these are both fascinating issues, I also think delusions present us with other philosophical questions that are worth consideration, especially once we start to think of delusions as patterns of thinking or cognition, rather than states.
To offer just one example, it seems to me that one puzzling aspect of delusional cognition is that subjects consider possibilities that would not even occur to most of us. Regardless of whether one comes to believe it or not, there is something odd about seriously entertaining the thought that an imposter has taken the place of one's spouse. This is true, I think, even on the assumption that subjects with the Capgras delusion have highly irregular experiences of familiar faces.
If this intuition is on the right track, it suggests that, at least in some cases, delusional subjects consider a set of things (propositions/hypotheses) to be possible that is different from what ordinary subjects do. This raises some interesting questions about ordinary empirical reasoning, hypothesis generation, and the different ways in which ordinary thinkers and delusional subjects envision modal space.
In my most recent work, I begin to explore this last idea in more detail. I claim that delusional subjects have irregular conceptions of epistemic possibility and that this is a significant respect in which their cognition is disordered (those who are attending can hear more at the upcoming ESPP conference - espp2013.com). If that is right, it naturally presents some further puzzles. Why do these subjects have such unusual conceptions of epistemic possibility? How does a subject's sense of what is possible influence belief fixation? These are the kinds of questions I am currently wondering about.
More generally, however, it seems to me that there are many underexplored issues when it comes to delusions, which makes it a very exciting time to work on imperfect cognitions...