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.

Box 61–1 Cognitive Therapy

Dissatisfaction with psychological treatments based on Freud’s theories of unconscious motivation intensified in the middle of the 20th century. Not only did these theories have no relevance to experimental psychology, but more importantly there was no empirical evidence that psychodynamic treatments actually worked.

The first form of alternative psychological therapy to emerge from laboratory studies is known as behavior therapy. The fundamental assumption of this approach is that maladaptive behavior is learned and can therefore be eliminated by applying the Pavlovian and Skinnerian principles of stimulus-response learning. So, for example, a child who has been attacked by a dog can become fearful of all dogs. This fearful response can be extinguished if the child learns that the conditioned stimulus (the sight of a dog) is not followed by the unconditioned stimulus (being bitten).

Behavior therapy was shown to be quick and effective for many disorders such as phobias. However, many mental disorders are better characterized in terms of maladaptive thinking rather than maladaptive behavior. In the 1960s Aaron Beck and Albert Ellis initiated a new kind of therapy in which the principles of learning are used to change thoughts rather than behavior. This is known as cognitive therapy or cognitive behavior therapy.

This form of therapy has been particularly successful in the treatment of depression. Depression is typically associated with negative thoughts (eg, remembering only the bad things that have happened to me) and negative attitudes (believing that I will never achieve my goals). Cognitive therapists teach their clients methods for reducing the frequency of these negative thoughts and changing their negative attitudes into positive ones.

Conscious and Unconscious Cognitive Processes Have Distinctive Neural Correlates

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 Helm-holtz’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.

Figure 61-1 Unconscious processing in cases of spatial neglect. After damage to the right parietal lobe many patients seem to be unaware of the left side of space (unilateral neglect syndrome). Shown the two drawings reproduced here, such patients said that the two houses looked the same. However, they also said that they would prefer to live in the lower house, indicating unconscious processing of the fire in the other house. (Adapted, with permission, from Marshall and Halligan 1988.)

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.

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

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.

Figure 61-2 Ambiguous figures. If you stare at the figure on the left (the Rubin figure) you sometimes see a vase and sometimes two faces looking at each other. If you stare at the figure on the right (the Necker cube) you see a three-dimensional cube, but the front face of the cube is sometimes seen at the bottom left and sometimes at the top right. In each figure the brain finds two equally good, but mutually exclusive, interpretations of what is there. Our conscious perception spontaneously alternates between these two interpretations.

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).

Figure 61-3 Neural activity associated with ambiguous visual information. An ambiguous stimulus was created by simultaneously presenting a face to one eye and a house to the other eye. Brain activity was measured while subjects observed these images. Subjects were instructed to press a button whenever a spontaneous switch in perception occurred (because of binocular rivalry). When the face is perceived (left), activity increases in the fusiform face area (FFA); when the house is perceived (right), activity increases in the parahippocampal place area (PPA). (Reproduced, with permission, from Tong et al. 1998.)

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.

Figure 61-4 Neural activity associated with visual hallucinations. Some patients with damage to the retina experience visual hallucinations. The location of the neural activity and the content of the hallucination are related. The experience of colors, patterns, objects, or faces, is associated with heightened activity (red) in specific regions of inferior temporal cortex. The fusiform gyrus is shaded blue for reference. (Reproduced, with permission, from ffytche et al. 1998.)

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).

Figure 61-5 Brain activity with and without awareness. Activity in the fusiform face area increased when the face viewed by subjects changed, whether subjects were unaware of the change (A) or conscious of it (B). When subjects were aware of the change, activity in parietal and frontal cortex also increased. (Reproduced, with permission, from Beck et al. 2001.)

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.