61: Disorders of Conscious and Unconscious Mental Processes

• Conscious and Unconscious Cognitive Processes Have Distinctive Neural Correlates

• Differences Between Conscious Processes in Perception Can Be Seen in Exaggerated Form after Brain Damage

• The Control of Action Is Largely Unconscious

• The Conscious Recall of Memory Is a Creative Process

• Behavioral Observation Needs to Be Supplemented with Subjective Reports

  • Brain Imaging Can Corroborate Subjective Reports

  • Malingering and Hysteria Can Lead to Unreliable Subjective Reports

• An Overall View

Although cognitive neuroscience emerged at the end of the 20th century as a major new discipline, a precise meaning of the term cognition can often appear elusive. The term is used in different ways in different contexts. At one extreme the "cognitive" in cognitive neuroscience has replaced the older term information processing. In this sense cognition is simply what the brain does. When cognitive neuroscientists speak of visual features or motor responses being represented by neural activity, they are using concepts of information processing. From this point of view the language of cognition provides a bridge between descriptions of neural activity and behavior because the same terms can be applied in both domains.

At the other extreme the term "cognition" refers to those higher level processes fundamental to the formation of conscious experience. This is what is meant in the term cognitive therapy, an approach to treatment pioneered by Aaron Beck and Albert Ellis and developed from behavior therapy. Rather than trying to change a patient's behavior directly, cognitive therapy has the aim of changing the patient's attitudes and beliefs (Box 61–1).

In common parlance the term "cognition" means thinking and reasoning, a usage closer to its Latin root cognoscere (getting to know or perceiving). Thus the Oxford English Dictionary defines it as "the action or faculty of knowing." Indeed, we know the world by applying thinking and reasoning to the raw data of our senses.

Used in this way there can be many kinds of disorders of cognition. After brain damage some patients can no longer understand the raw data supplied by their senses. This type of disorder was first delineated by Sigmund Freud and called an agnosia or loss of knowledge (see Chapter 17). Agnosias can take many different forms. A patient with visual agnosia can see perfectly well but is no longer able to recognize or make sense of what he sees. A patient with prosopagnosia has a specific problem recognizing faces. A patient with auditory agnosia might hear perfectly well but is unable to recognize spoken words.

Cognition is sometimes impaired from birth, so that a person has difficulty in acquiring knowledge. This might lead to general mental retardation or, if the problem is more localized, to specific learning difficulties such as dyslexia (difficulty learning about written language) or autism (difficulty in learning about other minds). Finally, cognition can become aberrant so that the knowledge acquired about the world is false. These disorders of thinking lead to false perceptions (hallucinations) and false beliefs (delusions) associated with major mental illnesses such as schizophrenia.

Cognition, deriving knowledge through thinking and reasoning, is one of the three components of consciousness. The other two are emotion and will. It used to be taken for granted that thinking and reasoning were under conscious voluntary control, and that cognition was not possible without consciousness. By the end of the 19th century, however, Freud developed a theory of unconscious mental processes and suggested that much human behavior was guided by motivations of which we are not aware.

Of more direct importance for neuroscience was the idea of unconscious inferences, originally proposed somewhat earlier by Helmholtz. Helmholtz was the first to carry out quantitative psychophysical experiments and to measure the speed with which signals are conducted in peripheral nerves. It had been thought that sensory signals arrived in the brain immediately (with the speed of light), but Helmholtz showed that nerve conduction was actually quite slow. He also noted that reaction times were even slower. These observations implied that a great deal of brain work intervened between sensory stimuli and conscious perception of an object. Helmholtz concluded that much of what goes on in the brain is not represented in consciousness and that what does enter consciousness (ie, what is perceived) depends on unconscious inferences. In other words, the brain uses evidence from the senses to decide on the most likely identity of the object that is causing these sensations but does this without our awareness.

This view was extremely unpopular with Helmholtz's contemporaries, and indeed still today. Most people believe that consciousness is necessary for making inferences and that moral responsibility can be assigned only to decisions that are based on conscious inferences. If inferences could be made without consciousness, there could be no ethical basis for praise or blame. Helmholtz's ideas about unconscious inferences were largely ignored.

Nevertheless, by the middle of the 20th century evidence began to accumulate in favor of the idea that most cognitive processing never enters consciousness. After the invention of electronic computers, the discipline of artificial intelligence (AI) was born and researchers began to study how and to what extent machines could perceive the world beyond themselves. It rapidly became clear that many apparently simple perceptual processes, when defined as a set of computations, are actually very complex.

Visual perception is the prime example. In the 1960s almost no one realized how difficult it would be to build machines that could recognize the shape and appearance of objects. We now know that it is very difficult. A fundamental question is how to work out which edges go with which object in a typical cluttered visual scene containing many overlapping objects. No one thought visual perception was difficult because it seemed so easy for us. I look out of the window and I see buildings, trees, flowers, and people. I am not aware of any mental processes behind this perception. Instead, my awareness of all these objects seems instantaneous and direct. The computational approach to vision revealed the underlying neural processes on which our seemingly effortless perception of the world depends. Similar processes underlie all sensory perception and especially the perception of sounds as speech. Most neural scientists now believe that only percepts, but not cognitive processing, are conscious phenomena.

The evidence for unconscious cognitive processes comes not only from artificial intelligence studies but also studies of cognition in people with brain damage. The effects of unconscious processes on behavior can be demonstrated most strikingly in certain neurological patients, such as those with "blind sight," a disorder first delineated in the 1970s by Lawrence Weiskrantz. These patients have lesions in the primary visual cortex and claim to see nothing in the part of the visual field served by the damaged area. However, when asked to guess, they are able to detect simple visual properties such as movement or color far better than is expected by chance. Despite having no sensory-based perception of objects in the blind parts of the visual field, these patients do have unconscious information about the objects and this information is available to guide their behavior.

Another example is unilateral neglect because of lesions in the right parietal lobe (see Chapter 17). Patients with this disorder have normal vision, but they ignore objects on the left side of the space in front of them. Some patients even ignore the left side of individual objects. In one experiment by John Marshal and Peter Halligan patients were shown two drawings of a house. The left side of one house was on fire (Figure 61–1). When asked if there were any differences between the houses, patients replied "no." But when asked which house they would prefer to live in, they chose the house that was not burning. This choice was thus made on the basis of information that was not represented in consciousness. These are just two examples of the abundant empirical evidence for the existence of unconscious cognitive processes in addition to the aspects of cognition familiar to us through introspection.

Currently one of the most exciting programs of research in neuroscience concerns the search for the neural correlates of consciousness (NCC) initiated by Francis Crick and Christopher Koch (see Chapter 17). The aim of this program is to demonstrate qualitative differences between the neural activity associated with conscious and unconscious cognitive processes. This research is important not only because it may give us answers to the difficult question of the function of consciousness but also because it is relevant to our understanding of many neurological and psychiatric disorders. The weird experiences and delusional beliefs of patients with certain cognitive disorders were once dismissed as beyond understanding. Cognitive neuroscience provides us with a framework for understanding how these experiences and beliefs can arise from specific alterations in normal cognitive mechanisms.

In many circumstances perception can change without any change in sensory stimulation. This phenomenon is illustrated by ambiguous figures such as the Rubin figure and the Necker cube (Figure 61–2). In other circumstances a big change in sensory stimulation can occur without the observer being aware of this change—the perception remains constant. A compelling example of this is change blindness.

To demonstrate change blindness two versions of a complex scene are constructed. In one well-known example developed by Ron Rensink the picture consists of a military transport plane standing on an airport runway. In one of the two versions an engine is missing. If these two pictures are shown in alternation on a computer screen, but critically interspersed with a blank screen, it can take minutes to notice the difference even though it is obvious when pointed out. (See Figure 29–3 for another example.)

In light of these examples we can explore some simple questions about the relationship between neural activity and conscious and unconscious cognitive processes. We can identify the neural activity associated with changes in perception when there is no change in sensory stimulation. We can discover whether changes in sensory input are registered in the brain even if not represented in consciousness. We can ask whether there is some qualitative difference between the neural activity associated with conscious as opposed to unconscious processes.

Two important results have emerged from studies that seek to identify the neural activity associated with specific types of percepts. The first is that certain kinds of conscious percepts are related to neural activity in specific areas of the brain. When we perceive the faces in the Rubin figure, there is more activity in the area of the fusiform gyrus, which is specialized for the processing of faces. Those brain areas that are specialized for recognition of certain kinds of objects (faces, words, landscapes, etc.) or for certain visual features (color, motion, etc.) become more active when the object or the feature is consciously perceived (Figure 61–3).

This observation also applies to deviant perception (hallucinations). After degeneration of the peripheral visual system leading to blindness, some patients experience intermittent visual hallucinations (Charles Bonnet syndrome). These hallucinations vary from one patient to another. Some patients see colored patches, others see grid-like patterns, and some even see faces. Dominic ffytche has found that these hallucinations are associated with increased activity in the secondary visual cortex, and the content of the hallucination is related to the specific locus of activity (Figure 61–4). Schizophrenic patients frequently experience complex hallucinations, which usually have the form of voices talking to or about the patient. These hallucinations are associated with activity in the auditory cortex.

These observations suggest that conscious experience may result from activity in certain cortical regions. This idea is difficult to test experimentally. Nevertheless, in the 1950s the neurosurgeon Wilder Penfield showed that electrical stimulation of the cortex in patients undergoing neurosurgery can give rise to conscious experience. Transcranial magnetic stimulation of the cortex in the region of V5/MT can lead to seeing moving light flashes.

The second important conclusion drawn from studies that seek to correlate neural activity and specific percepts is that activity in a specialized area is necessary but not sufficient to yield conscious experience. For example, in the change blindness paradigm subjects are often unaware of large changes in the picture they are viewing. If the change involves a face, activity is elicited in the fusiform gyrus whether or not the subject is aware of the change. But when the sensory change is also perceived consciously there is, in addition, activity in parietal and frontal cortex (Figure 61–5).

These observations are relevant to our understanding of unilateral neglect. It may be that the damage in the right parietal cortex simply prevents the formation of conscious representations of objects on the left side of space, since objects on the left side still elicit neural activity in the visual cortex. That is, sensory activity may support an unconscious inference in patients that they would not want to live in the house that is burning on the left side.

In normal people stimuli that do not enter awareness can nevertheless elicit overt responses. A face with a fearful expression elicits a fear response in the autonomic nervous system, measured as an increase in skin conductance (galvanic response) because of sweating. This response occurs even if the face is immediately followed by another visual stimulus, such that the face is not consciously perceived. There may be an advantage to having a rapid but poor resolution system for avoiding dangerous things. We jump first and only later, on the basis of a slow, high-resolution system, become aware of the identity of the object that made us jump (see Chapter 48). Damage in one or the other of these two recognition systems can explain certain otherwise puzzling neurological and psychiatric disorders.

Prosopagnosia is a perceptual disorder in which faces are no longer recognizable. The patient knows he is looking at a face but cannot recognize the face, even the face of his wife. The problem is specific to faces and the visual system. The patient may still be able to recognize his wife from her clothes, her gait, and her voice.

Actually, patients with prosopagnosia are able to identify faces but they do so unconsciously. They show autonomic responses to familiar faces and do better than chance when asked to guess whether or not faces shown to them belong to people who are familiar. In fact, they may use their awareness of the autonomic (emotional) responses elicited by a face to judge familiarity.

Capgras syndrome, a delusion that is occasionally observed in schizophrenic patients and in some neurological patients, shows the opposite pattern. These patients firmly believe that someone close to them, usually a husband or wife, has been replaced by an impostor. They claim that the person, although similar if not identical in appearance, is in fact someone else. Often this delusion is acted on with the demand that the impostor leave the house. In one extreme case a patient accused his stepfather of being a robot and subsequently decapitated him to look for batteries and microfilm in his head.

Haydn Ellis and Andy Young have suggested that this bizarre delusion is the mirror phenomenon of prosopagnosia. According to this view, the processing stream for face recognition is intact, but the stream that mediates the emotional response to the face is not functional. As a result, patients recognize the person in front of them but, because the emotional response is lacking, feel that there is something fundamentally wrong. This account has been partially confirmed by the observation that these patients do not have normal autonomic responses to familiar faces.

This explanation implies that Capgras delusions are not the consequence of disordered thinking but of disordered experience. A patient sees the face of his wife without having the normal emotional response. The conclusion that this is not his wife but an impostor is a cognitive response to this abnormal experience, the mind's attempt to explain experience.

The sense that we are in control of our own actions is a major component of consciousness. But are we aware of all aspects of our own actions? David Milner and Mel Goodale studied intensively a patient known as D.F. who demonstrates a striking lack of awareness of certain aspects of her own action. As a result of damage to her inferior temporal lobe caused by carbon monoxide poisoning, D.F. suffers from form agnosia. She is unable to perceive the shapes of things. She cannot distinguish a square from an oblong card and cannot describe the orientation of a slot. Yet when she picks up the oblong card to place it through the slot she orients her hand and forms her grasp appropriately (Figure 61–6). D.F. is able to use sensory information about the shapes of objects to guide reaching and grasping movements, but this information is not conscious.

This unconscious guidance system is not unique to patients with brain damage. It is simply revealed more starkly in the case of D.F. by the damage to the system that normally brings visual information about shape into consciousness. Indeed, we can all make rapid and accurate grasping movements without being aware of the perceptual and motor information that is being used to control these movements. Sometimes we are not even aware of having made the movement. This largely unconscious system for visually guided reaching and grasping is analogous to, and probably overlaps with, the rapid but poor-resolution system associated with fear responses.

Although we may not be aware of the perceptual and motor controls of actions like reaching and grasping, we think we consciously control our actions because we decide on an action and then initiate it. But what aspects of an action are we actually aware of? In an influential experiment by Benjamin Libet subjects were asked to lift a finger "whenever they felt the urge to do so." During this experiment Libet used EEG to measure the "readiness potential," a change in brain activity that occurs up to one second before a subject makes any voluntary movement. The time at which subjects reported feeling the urge to lift a finger occurred hundreds of milliseconds after the beginning of this readiness potential.

Later studies by Patrick Haggard and Martin Eimer revealed that the time of awareness of the urge to act is correlated with the time at which the evoked potential in brain activity measured over the scalp ceases to be medially located and shifts toward the side of the brain that controls the movement, contralateral to the hand that will move. This observation suggests that we are not aware of intending to make a voluntary movement until the nature of that movement has been precisely specified in a motor plan.

The results of these experiments have generated much discussion among philosophers as well as neural scientists concerning the existence of free will. If brain activity can be used to predict when someone is going to act before they are aware of having the urge to perform that act, does this mean that these urges are predetermined and our experience of freely willing them is an illusion? The decision to act might still be made freely but made without awareness. The awareness of the choice comes later. This implies that the unconscious inferences proposed by Helmholtz occur in the motor domain as well as the sensory domain. However, even if we leave open the possibility that free will may operate unconsciously, we are left with the moral dilemma whether people can be held responsible for decisions that are made unconsciously.

Libet also measured the time at which his subjects became aware of initiating an action. This awareness is a distinct event, later than the awareness of the urge to act. In contrast to the awareness of the urge, which is later than the associated brain activity, awareness of initiating the act occurs before the act itself begins. The time at which we become aware of initiating a movement occurs some 80 ms before the movement actually starts (Figure 61–7), while any sensory feedback from the movement will occur 100 ms or so after the movement has actually started.

Thus the awareness of initiating a movement is much too early to be based on any sensory feedback. What we are aware of must be based on expected rather than actual sensory information. We are very surprised if the actual sensations do not match what we predicted, as when we pick up an object that is much lighter than anticipated (see Chapter 33). Furthermore, if the difference between predicted and actual sensations is small, the predicted sensation dominates our awareness.

Pierre Fourneret and Marc Jeannerod required subjects to draw a vertical line using a computer's mouse. The subjects could not see their hand and so could not see that the computer introduced a distortion in the line displayed on the screen. In one test subjects had to move their hand at an angle of 10 degrees to the left to produce a vertical line on the screen (Figure 61–8). In other tests different degrees and directions of distortion were applied. The striking result was that subjects were not aware that the direction of their movements did not match the direction of the line they saw on the screen. When subjects were asked to repeat a movement that had actually deviated 10 degrees to the left, but were not shown the line they were making on the screen, they actually performed the straightforward movement that they thought they had just made. It would seem that as long as the goal is realized (drawing a straightforward line), we are aware of the expected sensory feedback, not the actual sensory feedback.

The idea that we are normally aware of expectations about movements rather than the actual sensations helps us to understand otherwise bizarre experiences. For example, after the amputation of a limb, patients experience a phantom limb (see Chapter 17). Some patients believe they can move this phantom just as they could previously move the real limb. Amputees still experience the urge to move the missing limb, and they can select specific movements they want the missing limb to make. As a result, their unconscious sensorimotor systems predict the sensations they would feel if they were to make the movement. It is these predicted sensations that dominate our normal awareness of action and provide the basis for the sensation of a moving phantom limb.

For most of us memory is the conscious reliving of a past experience in our imagination. From a behaviorist point of view, however, memory and learning are processes by which our past experience alters future behavior. Our behavior is often affected by past experience without our being aware of the memory or the influence it is having on us. Once again, such effects are seen in their most striking form in patients with damage to certain areas of the brain.

Some patients become densely amnesic after damage to the medial regions of the temporal lobe (see Chapter 67). These patients show no decline in intellect as measured by IQ tests but cannot remember anything for more than a few minutes. Although devastating, this memory impairment is actually rather circumscribed. The problem is largely manifested in declarative memory, and most severely in a type of declarative memory called episodic memory, the ability to recollect events in one's life (see Chapter 67). Procedural memory, in which consciousness has a minor role (see Chapter 66), remains intact. Thus patients still remember motor skills such as riding a bicycle and can often learn new motor skills at a normal rate. These different effects of brain damage on memory can lead to dramatic dissociations. A patient who has been learning some new skill everyday for a week will deny ever having performed the task before. He is then surprised to find how skillful he has become.

Normal people routinely learn skills unconsciously, although this is much more difficult to demonstrate convincingly. Several studies of procedural learning have used "choice reaction-time" paradigms. For example, subjects presented with four buttons that light up in sequence have to press as quickly as possible each button after it lights up. The subject is not told that the buttons light up in a particular sequence. Of course, knowledge of this sequence would enable the subject to predict which signal will come next and thus to respond more rapidly. In fact, responses do become faster once the sequence can be predicted, even when the subject is entirely unable to describe the sequence.

Another widely used protocol tests subjects' ability to recall lists of words they have memorized, a task that taps a form of declarative memory. In the recall phase a subject is presented with a list of the words that were on the study list plus new words. An amnesic patient has great difficulty with this type of task and may misclassify most of the previously seen words as new since she cannot recall seeing them before. Nevertheless, the brain activity elicited by reading old words is different from that elicited by the new words. Thus there is unconscious recognition of a difference, equivalent to that shown by patients with unilateral neglect or prosopagnosia. Normal subjects usually find this task easy, but they too will occasionally misclassify old words as new; as with amnesiacs, the evoked brain response registers the distinction lost to conscious retrieval (Figure 61–9).

Occasionally a subject misclassifies a new word as an old one. This misclassification amounts to a false memory. Such misclassifications are most likely to occur when the new word is semantically related to one or more of the old words. If the list of old words contained big, great, huge, then the new word large is likely to be identified as old. One explanation for this is that the perception of the new word large has been unconsciously primed by the previous presentation of the old words. Thus the new word large is processed easily and quickly. Because the subject is aware of this perceptual fluency, he concludes the word must be familiar and classifies it as old.

This observation emphasizes that memory is a creative process. Our conscious memories are constructed from both conscious recall and unconscious knowledge. To guard against false memories, as with false percepts, we use our knowledge about the world to determine what memories are plausible.

In some patients the process by which memories are screened seems to become dramatically disturbed. If asked what happened yesterday, most patients with amnesia will say that they cannot remember. However, a few will give elaborate accounts that do not correspond to reality. Such false memories are called confabulations. These memories can sometimes be extremely implausible. For example, one patient said that he had met Harold Wilson (a former British Prime Minister) and discussed a building job they were both working on.

In some cases these false memories are arbitrary constructions, as if the patient would rather make something up than admit that he does not know. In other cases the false memories are very specific and consistent. For example, one patient with brain damage caused by a fall, studied by Paul Burgess, became convinced that one of the nurses on the rehabilitation ward in England was the same nurse that had looked after him in the intensive care unit in the United States. He also believed that this nurse had stolen his watch and was having an affair with his wife. This patient was able to discuss all other subjects perfectly rationally but was entirely convinced of the truth of his memories about the nurse despite all evidence to the contrary.

False memories of this kind can be indistinguishable from the false beliefs expressed by patients with schizophrenia. Paranoid delusions similar to those described above are common, but some delusions can be even more obviously at odds with reality. One patient studied by Alan Baddeley believed he was a rock guitarist and a Russian chess grand master, even though he cannot play the guitar or chess and does not speak Russian. "But if you don't speak Russian, isn't that rather odd for a Russian chess player?" "Yes, well, I don't speak Russian, but I think it is possible that I've been hypnotized to forget things like the fact that I can speak Russian."

This patient's beliefs seem no longer to be constrained by his knowledge and experience of the world. Furthermore, the problem is self-sustaining as the patient's false beliefs become part of his knowledge of the world. Nevertheless, if our conscious perception and memory were too strongly constrained by our prior knowledge, we would never be able to see anything new or remember anything unusual. The neural mechanisms by which beliefs are acquired and fixed have as yet been only minimally investigated, but the various phenomena described above indicate how a research program might be initiated.

By the middle of the 20th century it had become clear that the classic behaviorist approach was inadequate for the exploration of many psychological processes. Language acquisition, selective attention, and working memory cannot be understood in terms of relations between stimuli and responses, however complex the relationships postulated.

The demonstration that some cognitive processes are unconscious requires that we move even further from behaviorism. If we want to explore the whole range of conscious and unconscious cognitive processes we will not be able to do so by focusing on overt behavior alone. We must not assume that a subject making purposeful, goal-directed actions is necessarily aware of the stimuli eliciting the action or even of the action itself. We must supplement behavioral observations with subjective reports. We have to ask the subject, "Did you see the stimulus? Did you move your hand?"

During the decades in which psychology was dominated by behaviorism, subjective reports were not considered an appropriate source of data. As a result, methods for recording subjective reports lag far behind methods for studying overt behavior. Regrettably, many studies of cognitive processes still make no systematic attempt to record subjective experience because of the long tradition of excluding subjective reports. One hundred years ago introspection was the major method for obtaining data in psychology. How else could one study consciousness? However, different schools of psychology obtained different results and, as John B. Watson emphasized, there seemed to be no objective way of deciding who was right. How can you independently confirm subjective experience? Thus the method fell into disrepute.

Subjective reports are usually verbal—our subject tells us in words what the experience was like for him or her. But they need not be verbal. In many experiments a human subject may indicate that he or she has seen the stimulus by pressing a button. Pressing a button is an observable behavior, but the behavior is an indicator of a conscious thought.

This kind of nonverbal report can also be used in experiments with monkeys. When presented with an ambiguous figure such as the Rubin vase, a monkey can be trained to press one button when it sees the face and another button when it sees the vase. The choice about which button to press must be based on introspection. Robert Hampton used this technique in a memory experiment. A monkey was asked to distinguish familiar and new objects. This task is typically presented in a forced-choice format. The monkey (or person) is presented with a familiar object and a new object and has to choose the familiar one. A correct choice might occur because the familiar object is consciously recognized. If no conscious recognition occurs then the monkey (or person) must guess. Some of these guesses may be right, because of cues arising from unconscious processes, but many will be wrong.

Incorrect guesses can be avoided if the response "Don't know" is permitted (indicated by not pressing either button). With this format the proportion of button presses that are wrong should be reduced because guesses have been eliminated. Here again the behavior of pressing the button is partially based on introspection: If I am aware that I do not know the answer, I will not press a button. Monkeys are able to improve their performance (and thus get more food rewards) when given the opportunity not to make a choice, suggesting that they know when they are guessing.

Brain Imaging Can Corroborate Subjective Reports

The problem of verifying subjective reports can be partially addressed with the use of brain imaging. Brain imaging studies have shown that neural activity occurs in localized areas of the brain during mental activity unaccompanied by any overt behavior. The content of such mental activity, such as imagining or daydreaming, can only be known from the subject's reports.

If we scan a subject while he says he is imagining moving his hand, activity will be detected in many parts of the motor system. In most motor regions this activity is less intense than the activity associated with an actual movement, but it is well above resting levels. Similarly, if a subject reports that she is imagining a face she has recently seen, activity can be detected in the "face recognition area" of the fusiform gyrus (Figure 61–10). In these examples the observed neural activity detected by the scanner provides independent confirmation of the experience reported by the subject. The content of consciousness can, in certain limited cases, be inferred from patterns of neural activity.

Malingering and Hysteria Can Lead to Unreliable Subjective Reports

When we record reports of subjective experience we are using the subject like a meter. Just as a meter can convert electrical resistance into the position of a pointer on a dial (reading 100 ohms) so a subject can convert the wavelength of a light source into the report of a color ("I see red.")

But there is a critical way in which the meter is not like a person. The meter does not experience red and cannot communicate meaning. And, while the meter might be faulty, it can never pretend to see red when it is really seeing blue. Most of the time we presume that subjective reports are true, that is, the subject is trying as far as possible to give an accurate description of his experience. But in some circumstances subjects might say "blue" even though what they saw was red. How could this arise and what is the status of the subjective report in such cases?

Consider a patient who has become amnesic as a result of extensive damage to the medial temporal cortex. Shown a photograph of someone whom he sees every day on the ward, the patient denies ever having seen this person before. But physiological measurements (electroencephalogram or skin conductance) made at the same time show a response to the photo (but not to photos of people he has not seen before). We conclude that conscious memory processes have been damaged while unconscious processes remain intact. This patient's subjective report is an accurate account of his conscious experience, but there are things he "knows" that do not enter consciousness.

Another patient is brought in having been found wandering on the street. There is no evidence of brain damage, but he has lost his memory to the extent of no longer knowing anything about himself or his history. He, too, denies any knowledge of the familiar people he is shown in photographs, but when tested he shows physiological responses to these familiar people. In this case, because of the lack of detectable brain damage (and other features of the memory loss), we begin to wonder about the truthfulness of his statements. Perhaps the physiological responses indicate that he does consciously recognize people. Subsequently the patient is identified by the police, and we discover that he is wanted for a serious crime committed in the neighboring county. Our doubts about the reliability of his reports increase. Finally, our suspicions are confirmed when he foolishly tells a fellow patient, "It's so easy to fool those clinical psychologists."

In this case we have direct evidence that the patient was deliberately misleading us about his conscious experience. In many ways the ability to deceive is the pinnacle of all human attainments, for to deceive others we must not only be conscious of our own mental state but also of their state. Is there some way we could have discovered from our patient's behavior that he was deceiving us? One approach is to use a memory test of the kind discussed earlier. The patient studies a list of words. He then sees a new list consisting of the words he has just studied and new words, and he must decide whether each word is old or new. A genuine amnesic would not recognize any of the words. He would have to guess. Through unconscious priming effects he might perform slightly better than chance. The malingering patient can recognize the old words but will have a strong tendency to deny that he has seen them before. Unless he is very sophisticated, he may perform worse than chance. It seems we can distinguish between the genuine amnesic and the malingerer.

A third kind of patient also simulates amnesia (or some other disorder) but does so unconsciously and thus is not a malingerer. Such a case would be called hysterical or psychogenic amnesia. Like the malingerer his performance on the recognition test is worse than chance. Nonetheless, he is not aware of his simulation. The same mechanism probably occurs in normal people who have been hypnotized and then told that they have no memory for what has just happened. This phenomenon is sometimes referred to as a dissociated state; that part of the mind that records experiences and makes verbal reports has become dissociated from the part that is creating the simulation. Hysterical simulations can create sensory loss, such as hysterical blindness, and motor disorders, such as hysterical paralysis or hysterical dystonia, as well as hysterical memory loss.

We are still a long way from understanding the cognitive processes or underlying physiology of these disorders. A key problem is how to distinguish hysteria from malingering. From the standpoint of conscious experience the two disorders are quite different: The malingerer is aware that he is simulating whereas the hysterical patient is not. Yet the patients' subjective reports and overt behavior in the two cases are very similar. Is there no measure that can distinguish between these different disorders? This may be one situation where studies of neural activity are the only way to make the critical distinction between these different states of consciousness.

The study of mental disorders forces us to confront the conceptual gap between the mental and the physical. It is no longer possible to maintain that some mental disorders have mental causes and others physical causes. There is now abundant evidence that a physical cause (abnormal brain function) can create a mental disorder such as the false belief that "My wife has been replaced by an impostor" (Capgras syndrome).

Cognitive neuroscience has had a major impact on our attempts to bridge this gap because its descriptive language, the language of information processing, can be applied simultaneously to psychological and neural processes. In Cartesian terms information is not physical since it is not extended in space or time. Yet information can be stored in physical devices such as memory sticks or books. Information theory and the associated development of the computer provided the first hint that perhaps science can address the question of how subjective experience can emerge from activity in a physical brain.

The cognitive neuroscience approach has been applied to many different mental abnormalities in both neurological and psychiatric patients. These studies have made clear that perception, action, and memory are the result of many parallel processes, and that although some of these processes support conscious experience, the majority occur below the level of awareness.

Striking abnormalities occur when some of these processes are damaged while others remain intact. An example presented in this chapter is D.F., a patient with damage to inferior temporal cortex. She is no longer consciously aware of the shape of an object and hence cannot describe it or recognize what it is. She can nevertheless form her hand into the appropriate shape to pick up the object. From the perspective of cognitive neuroscience, her problem can be described in terms of two kinds of representations that are needed for performing the two kinds of tasks. For reaching and grasping an object, its shape needs to be represented in hand-centered coordinates relating to the position of the hand that will do the grasping. For recognizing an object, an object-centered representation is required that is independent of viewpoint. In D.F. the latter kind of representation has been damaged while the former remains intact.

Although the control of action is largely unconscious, we are very much aware of ourselves as inhabiting and owning our bodies and as agents of action that causes things to happen in the world. These experiences of the self can also be upset by brain abnormalities. Overactivity in the right hemisphere at the junction of the temporal and parietal cortex can create "out-of-the-body" experiences, the experience of looking at one's body from the outside. Damage to the right hemisphere can cause one to look on a limb as "not me." These abnormal experiences can be explained as the result of faulty neural representations of the body and its parts in space.

Even more striking is the disorder of the experience of the self described by patients with schizophrenia. A patient with "delusions of control" experiences his actions as being under the control of an alien force: "My fingers pick up the pen, but I don't control them. What they do is nothing to do with me." This is not a problem of ownership. The patient knows it is his fingers that are moving. Instead, this is an abnormality in the experience of agency, the awareness of who or what is responsible for the fingers moving. Although we cannot yet describe the cause at the neural level, this symptom is associated with overactivity in parietal cortex, and there is increasing evidence that it is created by a failure to predict the sensory consequences of actions.

Many aspects of motor control occur without consciousness because the feedback sensations associated with movement are actively suppressed. This is because the sensory consequences of our own movements can be predicted on the basis of the information we use to generate the movements. This is why we cannot tickle ourselves. If I stroke the palm of my hand, the conscious sensation and the associated brain activity is greatly reduced in comparison to what occurs if someone else strokes my palm. I can predict what I am going to feel when I tickle myself. I cannot predict what I am going to feel if someone else tickles me. This is a rare example of cognitive neuroscience contributing to our understanding of conscious experience.

We now know why philosophers describe the experience of action as "thin and evasive." For patients with schizophrenia the experience of action is no longer thin and evasive, as the sensory consequences of their actions are not properly suppressed. When they make an active movement with their arm they experience all the sensations that normally occur only when their arm is moved passively by some external force. A cognitive model can thus explain the experience that leads patients with schizophrenia to believe that their actions are caused by alien forces. It remains to be seen whether this cognitive model can also help us understand the abnormality at the neural level.