So, following up an earlier post, I'm working my way philosophically through Chris Frith's latest book: Making up the Mind.
The Prologue of Frith's book sets out the following argument. (I reconstruct):
1) When you have a subjective experience such as a visual illusion, this only occurs 'in your mind'. (Frith likes to use objectifying metaphors such as the following: if I experience a visual illusion of moving dots, then the 'movement is only happening in my mind'.) 'The only way I can know about the things in your mind is because you tell me about them.' ... 'there is no way I can get into your mind and check ... your experience'.
2) But this seems to be a problem for the psychologist who wants to be considered a proper scientist. As scientist's we don't like to have to go on people's subjective say-so. We want to be able to check. (Frith asks of a synaesthetic friend: 'why should I believe her when she says these are direct sensory experiences that she cannot control?') And scientific psychologists also want to be able to objectively measure the mind. 'there are... properties of the mind that are common to us all. It is these fundamental properties that psychologists are trying to discover.' Frith is confident that 'in time, psychologists will have discovered what to measure and ... developed the instruments ... to make these measurements very precisely'. But, he considers in passing, perhaps this confidence is misplaced, since we cannot check up on the subjective reports of others. How do we know if the subjective experiences are the same for everyone?
3) Thankfully, 'big science' - PET and fMRI scans - comes to the rescue. We can look to see what is happening in people's brains at the very moment that they report their subjective experiences. The 'problem with psychology is solved. We no longer need to worry about these soft, subjective accounts of mental life. We can make hard, objective measurements of brain activity instead.'
But here's the problem: What licenses the inferences from what I see in the scanner to what is going on in the person's mind? If 1) genuinely does represent some kind of a problem in need of a solution, then it had better not be that the solution (brain scans) depend on correlations between what is scanned and the say-so of the scannees about what they are imagining. After all, it is precisely this testimony that I'm not supposed to be relying on - and it is precisely by turning to the 'hard science' of brain scans that I am supposed to be able to avoid having to rely on what the scannee says.
But perhaps here's a way out. Frith tells us that he and a few of his colleagues have 'always been ... interested in the brain activity associated with purely mental events. We have found that when a volunteer imagines he is pressing a button, then the same brain areas become active as when he is really pressing a button. If we had no brain scanner, there would be absolutely no objective sign that our volunteer was imagining pressing a button. ... We assume that he is following our instructions to imagine that he is pressing the button every time he hears the signal.'
Maybe it is this, then, that licenses the inference from scanner result to subjective goings on. We know for sure when a person is really pressing a button. We don't know, aside from by relying in a putatively un-scientific manner on his say-so, when he is merely imagining that he is pressing a button. However when we put him in the scanner we find some part of the brain that lights up both when he is really button-pressing, and when he is merely imagining it.
Doesn't this solve the problem? I think not, and here's why. The 'big science' here is still only as good as the 'soft science' on which it is still based. Someone is pressing the button: parts A, B, C, & D of their brain always light up when they do. For someone else not actually pressing the button, parts C & D of their brain sometimes light up, or perhaps it's parts B & C. How do I know whether this second person is imagining pressing the button? I'm not allowed to ask them, since this would be to submit to the perils of soft science. Nor can I just say that "to have parts C & D light up without A & B just is to imagine pressing a button", since that amounts to tacitly changing the subject - from psychology to neurology. In truth there's no answer to the question given the constraints. If I want to find out whether sole B & C firing, or C & D firing, is correlated with imaginary button-pushing, I have to ask the scannee. Big science bottoms out in subjective testimony after all.
None of this is to say that, if we were worried that someone was tricking us about what they were imagining, and if we had already done lots of scans of trustworthy people imagining that they were button-pressing, and found what the consistent neural correlates of button-press-imagining were, then we might not want to resort to scanning them. But this isn't a case of 'big science saving soft science'. It wasn't because of fears of trickery that the psychologist hoped to be able to rely on brain scanners - to take a 'direct look' into the brain of the putative imaginer. It was because of some supposed scientific illegitimacy in relying on personal and hence 'subjective' testimony that the big science was being brought in.
For my own money, I'm not in the slightest worried that psychological science relies on testimony. That would only seem to be a problem if we took seriously the objectivising metaphors of the mind as a kind of inner place to which we only have access in our own case. If we ignored our Wittgensteinian or Rylean lessons and took those seriously, and if we thought of science as the objective exploration of worlds ('outer' or 'inner'), then we might want to try to avail ourselves of an apparatus (it would preferably be a mind scanner, but it seems that we have to settle for a brain scanner) to have a direct, independent, scout around in there. The problem with that is as described above: We still rely on testimony to make the inferences from brain to mind: our new neuropsychological science of the imagination is still soft at heart.
Take the metaphors less seriously, however, and we may be less inclined to feel disastrously external to one another. Perhaps, for example, much of the time my words directly avow or express my 'mental states' and 'mental processes' - rather than constituting my testimony, i.e. rather than constituting avowals or expressions of merely subjective beliefs, about what I find by way of goings on in my mind. And perhaps in those instances in which I do report rather than avow or express what I am inwardly doing - for example, instances such as imagining pressing a button - then my sincere say-so can be thought of as criterial, rather than merely empirical evidence, for what is thereby reported. Absent reasons to doubt it when you tell me what you're fantasying, and I need no help from big science scanners, telepathy, or God to come to the relevant conclusion: it just drops out deductively.