I’d like to thank Adam for the invitation to blog here. As he mentioned, my interest has been piqued by the recent study showing that a patient apparently in a persistent vegetative state showed brain activity indistinguishable from normal controls when asked to imagine certain actions. I won’t review the study here; Adam has already provided a pointer to popular summaries. Instead, I want to think about how we should interpret the findings, and about the ethical implications of the studies.
First, are the findings evidence of consciousness? Nicholas Schiff, a neuroscientist at Weill Cornell Medical College in New York, was quoted by the New York Times saying that the study provided “knock-down, drag-out” evidence for conscious activity (the authors of the study themselves are somewhat more cautious, suggesting that the patient is “probably” conscious). I beg to differ. It certainly provides evidence for the hypothesis that she is (perhaps minimally) conscious, but it is far from conclusive. The study shows, recall, that the patient is processing certain kinds of information. There was activity in brain regions associated with speech processing when she was presented with sentences in English, and extra activity when words or sentences were ambiguous. When she was asked to imagine engaging in activities, the relevant areas of the brain – the areas active in conscious controls – were active. This is strong evidence that she is processing the information in a way that is attuned to the semantic content of the sentences addressed to her. But it is not conclusive evidence that she is conscious.
In saying this, I am not supposing that there is anything spooky about consciousness. I am not supposing that consciousness cannot be investigated by imaging techniques. I am merely supposing that we do not – yet – know what counts as evidence for the presence of consciousness, but that we do know that evidence of processing is not evidence of consciousness. We already know that subjects who are, by most standard tests, unconscious engage in processing that is sensitive to the content of sounds they hear. Consider people in a state of automatism. They are able to engage in very complex series of actions, even driving cars while avoiding obstacles and obeying traffic signals. So long as the action is routine, they are capable of engaging in it. Or consider ordinary sleep. While you are asleep you engage in processing of sounds around you. Hence the well-known phenomenon of incorporating such sounds into one’s dreams (and the fact that the alarm clock wakes you). Subpersonal processing without consicousness - as in priming - is a very well-attested fact.
In many ways, this fascinating study is frustrating, because it demonstrates the limits of our knowledge about consciousness. Some of these limits seem very difficult to overcome, even in principle. Philosophers distinguish two kinds of consciousness: phenomenal consciousness, which is subjective experience, and access consciousness, which occurs when information is globally available for information processing. Neuroscientists routinely assume that the two are closely correlated. That is, they assume that if a subject is conscious of something, they can report it. But the assumption might be false. Suppose that we have subjective experiences that we cannot report, because they never become globally available. In that case, we will have experiences that we cannot express, or recall. If that’s right, investigating the neural correlates of consciousness will be almost impossible: we simply won’t know where to look. So there are several ways we might intepret this study. Here are just some.
(1) the patient is engaged in information processing like that of a sleeper, and - like the sleeper - is unconscious.
(2) The patient is engaged in information processing like that of a sleeper, and - like the sleeper - this processing is (phenomenally) conscious. But because this phenomenal consciousness is not access conscious, it is not available for reporting. Hence sleepers often fail to recall their dreams, and the woman can’t report her conscious awareness.
(3) Sleepers, and some PVS patients, are minimally conscious: there is some, reduced, awareness of surroundings.
Finally, and very briefly,what are the ethical issues raised here? Others have commented on the possibility that this case will raise hopes that are probably unfounded. The young woman in the study suffered comparatively little brain damage; that is, compared to many other PVS patients. It is also important that we see whether the study can be replicated. But I want to set these questions aside, and instead focus on the implicit assumption that the value of a life – to the person whose life it is – is proportional to her degree of conscious awareness.
In general, this assumption has a lot going for it: conscious experience may be what makes life worth living. A lot of philosophers have wondered what consciousness is for: given that we can get along without it, why did evolution go to all the trouble and expense (from the evolutionary point of view) of developing it? Whatever the answer to that question may be, it is plausible that moral value is something that comes with consciousness: it is only because we can experience (music, art, a lover’s touch, the taste of wine, pain and pleasure) that we are ends and not merely means (to speak with Kant). But it doesn’t follow that for this woman her life is better if she is conscious. In fact, she may be much worse off if she is conscious. If she has no prospect of recovering any control over her body, then she is a state that is much like locked-in syndrome, only worse. She is, if conscious, trapped in a state that must be horrifically frustrating and boring. If her responses are indicative of a good prognosis, then we should welcome these results. But if they are instead indicative of an indefinite future of consciousness without control, then they are not, for her, a good sign at all.