خود در عمل: درسهایی از هذیان های کنترل
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|30336||2005||19 صفحه PDF||سفارش دهید||10355 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Consciousness and Cognition, Volume 14, Issue 4, December 2005, Pages 752–770
Patients with delusions of control are abnormally aware of the sensory consequences of their actions and have difficulty with on-line corrections of movement. As a result they do not feel in control of their movements. At the same time they are strongly aware of the action being intentional. This leads them to believe that their actions are being controlled by an external agent. In contrast, the normal mark of the self in action is that we have very little experience of it. Most of the time we are not aware of the sensory consequences of our actions or of the various subtle corrections that we make during the course of goal-directed actions. We know that we are agents and that we are successfully causing the world to change. But as actors we move through the world like shadows glimpsed only occasional from the corner of an eye.
The diagnosis of schizophrenia is largely based on what patients report about their experiences and beliefs. These experiences and beliefs are typically labelled hallucinations and delusions and are considered to be abnormal because they are false. The experiences are false in the sense that they do not correspond to the sensory input. The beliefs are false in that they are not justified by the evidence. Since misperceptions and false beliefs in this sense are rather common in the general population a further requirement for the diagnosis of schizophrenia is that the false perceptions and false beliefs should be outside the normal range of experience and belief. An example of such a false perception associated with schizophrenia would be that the patient hears his thoughts spoken aloud just after he has thought them (thought echo). An example of a false belief would be the claim by the patient that other people can hear her thoughts just as well as if they were being spoken aloud (thought broadcasting). This characterisation of the experiences and beliefs of patients as being outside the normal range immediately raises a problem when we try to understand these symptoms. However hard a patient tries to give a truthful and accurate account of her experiences, she will inevitably have difficulty in communicating them. The patient has somehow to relate her own bizarre experiences to the more normal experiences shared between her and her listener (Jack & Roepstorff, 2002). Thus, though my starting point for this consideration of the experience of the self in schizophrenia is based on self-reports from patients, I will place great emphasis on second-order inferences about experience derived from behavioural paradigms. I believe we need to use such inferences to get a better understanding of what it is that patients are trying to communicate through their reports. The same problem, although to a lesser extent, applies to any self-report concerning the experience of action. Henry Ey highlighted this problem with the normal experience of the body, “Except in the case of difficulty, pain, embarrassment…, the body seems transparent and silent in the field of perception” (Ey, 1973). If our bodies in action are indeed so transparent and silent then we may need information from experiments to help us understand even our own experience of action.
نتیجه گیری انگلیسی
Since the original proposal that delusions of control in schizophrenia might be explained by a defect in self-monitoring there has been a dramatic increase in studies of the awareness of action in normal volunteers and in various patient groups. In the normal case the experience of action is indeed transparent. Our perception of the sensations caused by our actions is attenuated and we are not aware of the minor corrections made on the course of goal directed movements. These effects derive from our ability to predict the consequences of our movements. In contrast patients with delusions of control are abnormally aware of the sensory consequences of an action and cannot accurately predict the consequences of their movements. This leads to a feeling of not being fully in control of their actions. Their experience reflects a failure of forward modelling in the motor control system. There are two problems with this account. First, the failure of forward modelling must only be partial. A complete failure would lead to a much greater problem with motor control. Furthermore patients can use forward modelling to make predictive alterations of grip force in routine situations (Delevoye-Turrell et al., 2003). The problem seems to lie in the ability to make explicit (i.e., conscious) use of forward models, as when imagining a movement (e.g., Maruff et al., 2003). Knoblich, Stottmeister, and Kircher (2004) have shown that patients with schizophrenia are normal in their ability to use forward modelling to automatically adjust their hand movements to overcome discrepancies between these movements and their visual consequences, while at the same time being impaired in their ability to report the discrepancies. Once again this result emphasises that, for these patients, the problem is not with motor control, but with awareness of motor control. The existence of people with an impairment that is restricted to awareness raises interesting possibilities for addressing the question of what awareness is good for. The second problem with this account is that similar failures of forward modelling also occur in patients with parietal lobe damage (e.g., Sirigu et al., 1996), but these patients do not report delusions of control. In terms of underlying physiology patients with delusions of control show over-activity in parietal cortex (Spence et al., 1997). This observation suggests that their problem might lie higher in the hierarchy of control. The problem is not in parietal cortex, but results from some abnormality in the signals that modulate activity in parietal cortex during self-generated actions. These signals might well arise in prefrontal cortex; the source of willed action (Spence, Hirsch, Brooks, & Grasby, 1998). It remains to be seen whether this hypothetical failure of long-range cortico-cortical modulation can also explain the other experiential abnormality reported by patients with delusions of control; the feeling that the actions they are performing are intentional, but the intention is not theirs. There is preliminary evidence that patients with schizophrenia perceive agency where others see none (Blakemore, Sarfati et al., 2003). Perhaps it is this over-active tendency to perceive agency that gives the delusion of control its special flavour. The tendency to perceive agency where there is none may be a more general feature of schizophrenia. In patients with auditory hallucinations this tendency is coupled with a failure to predict the sensory consequences of speech (Ford & Mathalon, 2004). In patients with persecutory delusions the over-active tendency to perceive agency exists in isolation. Key questions concern the neural basis of our perception of agency and its relationship with the forward modelling system. I have deliberately avoided discussing those passivity experiences that involve thoughts and emotions. It would be pleasing if a similar account could be given for the experience of not being in control of one’s thoughts and emotions (e.g. Feinberg, 1978), but there are many problems to be resolved, especially if I continue to demand supporting evidence from behavioural experiments. I find the distinction between agency and ownership is more difficult to conceive in the case of emotions and thoughts. The patient experiencing made emotions reports that it is him having the emotion, but that it is being forced upon him (“It puts feelings into me: joy, happiness, embarrassment, depression. It just puts it in and I feel the glow spread over me.”). But in what sense do we ever feel that we are the agents of the emotions that we feel? The situation is even worse for thoughts (“Thoughts are put into my mind like ‘Kill God.’ It’s just like my mind working, but it isn’t. They come from this chap, Chris. They’re his thoughts.”). It is even more difficult to separate ownership from agency in the case of thoughts (but see Stephens & Graham, 2000). What do the studies I have reviewed here tell us about our normal experience of the self in action? Paradoxically it seems as if the mark of the self in action is that we have very little experience of it. Most of the time we are not aware of the sensory consequences of our actions or of the various subtle corrections that we make during the course of goal-directed actions. We know that we are agents and that we are successfully causing the world to change. But as actors we move through the world like shadows glimpsed only occasional from the corner of an eye. Neuroscience is beginning to cast some light on these shadows.