The Making of the Mind: The Neuroscience of Human Nature (15 page)

Two strange manifestations of the interpreter come from brain injured patients. Patients with anosagnosia lack knowledge of the fact that they are experiencing a severe neurological problem in the parietal lobe, which keeps track of the position of the body in space, monitoring the location of the left arm, for example. In anosagnosia, the patient denies awareness of the problem. An injury to the right parietal lobe disrupts the monitoring of the opposite side of the body, preventing perception of the left arm's current location. In Michael Gazzaniga's words, “Those who suffer from right parietal lesions and are hemiplegic and blind on the left side frequently deny they have a problem and claim the left half of their body is not theirs!”
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The anosagnosic patient with a right parietal injury cannot locate his left hand when asked to by a neurologist. The patient says that he does not know where his left hand is now located: “When a neurologist holds this patient's hand up to his face, the patient gives a very reasonable response: ‘That's not my hand, pal.’”
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The patient's explanation is a product of the left-brain interpreter trying to reconcile the perception of the hand with the seemingly deeper belief that the left hand does not exist.

A different kind of neurological disorder—a kind of amnesia—has similarly revealed the interpreter at work. Because of memory loss, the amnesic patient experienced confusion about her current residence. She believed she was in her home in Freeport, Maine, rather than in the Memorial Sloan Kettering Hospital in New York. Michael Gazzaniga recounted her response to his question of where are you as follows:

“I am in Freeport, Maine…I know you don't believe it, but I know I am in my house on Main Street in Freeport, Maine.” I asked “Well, if you are in Freeport and in your house, then how come there are elevators outside the door here.” The grand lady peered at me and calmly responded “Doctor, do you know how much it cost me to have those put in?” This patient has a perfectly fine interpreter trying to make sense of what she knows and feels and does.
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The interpreter then is a like a detective who looks for clues and tries to come up with a theory that explains the facts. On the other hand, the interpreter is not the kind of detective we admire, because it gladly accepts the most threadbare evidence; “case closed, time for the next one,” seems to be the operating policy of the mind's interpreter. There is no time to thoroughly investigate the cause, or more likely multiple causes, of an experience now arising in consciousness. The stream of consciousness usually moves too swiftly for thoroughness. New experiences will soon arise and the old will fade from working memory within half a minute unless heeded and recycled. Thus, the interpreter is like a very badly overworked detective who simply jumps on the first plausible theory that makes sense for the moment and moves on. Arriving at an immediate interpretation of consciousness, even if shaky, is apparently better than being at a loss for understanding.

The interpreter seeks explanations of our perceptions. It makes attributions about why events unfold as they do. It can be understood as the means by which the mind avoids uncertainty and maintains control. When viewed from this perspective, the interpreter should be especially active when faced with an acute feeling that matters are out of one's personal control. Then, the interpreter should especially seek to establish control by making connections, pulling together explanations, and seeking coherence even in the face of chaos.

A long line of research in cognitive science has documented that people make causal attributions about events as a means of maintaining personal control.
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It is the feeling that things are spinning out of control that motivates the human brain to find a pattern in events and try to predict what is going to happen next. The left-brain interpreter thus will be activated whenever the individual senses a lack of control. Superstitions and conspiracy theories can be seen as the societal consequence of the interpreter's drive to find a causal explanation for events that are seemingly out of control. Jennifer Whitson and Adam Galinsky gave two such examples:

Tribes of the Trobriand islands who fish in the deep sea, where sudden storms and unmapped waters are constant concerns, have far more rituals associated with fishing than do those who fish in shallow waters…. Baseball players create rituals in direct proportion to the capriciousness of their position (for
example, pitchers are particularly likely to see connections between the shirt they wear and success).
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In a laboratory study of personal control, the participants were shown a series of snowy, visually noisy pictures; half of the pictures contained a hidden figure and half contained nothing but noise. Half of the participants were first induced to feel a loss of control by trying to do a learning task in which they received phony feedback. Instead of being told when they responded correctly and when they did not, the feedback was entirely random. These participants in fact experienced a feeling of loss of personal control compared with those not receiving the phony feedback. It turned out that these vulnerable participants in fact were most likely to perceive meaningful figures in pictures that contained nothing but noise.
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After experiencing a loss of control, these individuals struggled to regain control by interpreting nothing as something. Their left-brain interpreter made sense of the noise by seeing a hidden figure where none existed most often in the group experiencing a lack of control.

WHY THE LEFT HEMISPHERE?

What, then, are the parts of the cognitive machinery called the interpreter? There are two: causal inference and inner-directed language. Both of these parts are housed in the dominant left hemisphere of the brain. The interpreter's work, however, is supported by memory regions that are distributed widely in both cerebral hemispheres.

Causal Inference

The interpreter discovers or makes up, if needed, an explanation for why things happen the way they do. One of the specialties of the left hemisphere, then, must be the capacity to make inferences. The events that comprise the stream of conscious experience are reflected upon by the left hemisphere and explained by making assumptions about cause and effect. Event A is inferred to be the cause of Event B, based both on observation of their relationship in time and on knowledge of how the world works. For example, if we first
observe a person shaking the branch of an apple tree and next observe an apple falling to the ground, then an inference is required to establish a causal relationship. The concept of force must be activated and seen as relevant to the observed facts. The force itself is hidden, but we likely infer that the shaking produced a force that caused the apple to fall. The force of gravity is also hidden, but from experience in the real world, we learn that unsupported objects fall to the ground. If the apple, dislodged from a branch, did not fall, then we would be very perplexed as to why it violated the scheme of our world knowledge. If the shaking did not dislodge the apple, then we would infer that the force exerted on the apple was insufficient, but we still would assume that a force was applied based on what we know from experience.

The causal inference just described is subtly different from the direct perception of causality. If instead of shaking the branch, the person directly strikes the apple and it falls, then no inference is required. We can visually perceive causality of one object affecting another. Direct perception of causality has been isolated as a specialty of the right hemisphere. Imagine a billiard ball—the white cue ball—rolls toward a stationary black eight ball. It strikes the eight ball, which then rolls in the same direction that the cue ball had been traveling. Using images on a computer screen, this scenario was presented to the left or the right hemisphere of a split-brain subject with the rolling ball labeled A and the struck ball labeled B. Inserting a time gap between A striking B and B starting to roll disrupts the perception of causation. Of interest, only the right hemisphere was sensitive to the experimenter delaying the movement of B.
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The left hemisphere was not adept at direct causal perception.

Now, consider a different task that requires causal inference. Imagine two switches, one green and one red, positioned above a light. The subject first observes that depressing the green switch turns on the light. Second, he observes that depressing both switches also turns on the light. Third, he observes that depressing the red switch only does not turn on the light. Fourth, he again observes that depressing both the green and red switches turns on the light. Finally, a probe is presented and the subject predicts what will happen to the light. Either a red probe or a green probe is presented. To successfully predict that the green, but not the red, probe should turn on the light,
the subject must make a causal inference. The causality cannot be perceived directly because a hidden force is involved related to the electrical wiring. The subject must reason that the light only comes on when the green switch is depressed, regardless of what happens with the red switch. The key finding with the split-brain patients shows that now the left hemisphere made the correct response to the two probes.
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The right hemisphere was unequipped to predict accurately because it failed to make an inference of causation.

The capacity for causal inference could be by itself a uniquely human characteristic. Experiments with apes and monkeys have demonstrated their ability to learn through trial and error how to use a stick as a simple tool to obtain food from a clear tube. They eventually get the hang of using the stick to push the food out of the tube, and in that sense they have some understanding of the concept of physical force. However, by modifying the task slightly, limitations in their understanding emerge. In the modified version, a small trap is added under one part of the clear tube. If the primates “appreciate the causal force of gravity and the physics of holes and sticks moving objects, they should learn to avoid this trap as they attempt to push the food through the tube (i.e., they should always push the food out the end away from the trap).”
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Neither capuchin monkeys nor chimpanzees get the hang of this version—it takes them dozens of trials to figure out avoiding the trap. By contrast, children only two or three years old “behave much more flexibly and adaptively on these tube problems—seeming to understand something of the causal principles at work—from the very earliest trials.”
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Imagine you observe a person shaking a tree and seeing an apple fall. Now, suppose a strong gust of wind in a violent storm shakes the tree and an apple falls. Your mind sees these two situations as identical at the level of inferred causation. In fact, you can predict that a good way to get an apple to fall would be to shake the branch yourself. Remember that the chimpanzee's mind is organized around perceptual episodes rather than in terms of abstract concepts, such as force. To the chimpanzee, these three situations are three different episodes. In the view of Michael Tomasello, “Non-human primates understand many antecedent-consequent relations in the world, but they do not seem to understand causal forces as mediating these relations.”
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Knowing that a strong gust of wind can shake an apple loose does not prompt the chimpanzee
to conclude that it might be a good idea to shake the branch on its own. Thus, the capacity for causal inference, as well as language, sets the interpreter of the human mind apart from even our most closely related species.

The visual and spatial stores of working memory support the inference capabilities of the interpreter. They provide temporary storage and replaying of perceived events. By holding in mind multiple events, hidden forces can be hypothesized and causal inferences reached. For example, holding in mind recollections of an apple falling from a tree when either the tree was shaken by the wind, by another person, or by the self, the inference that all of these events are linked becomes more likely. Working memory can also be used to imagine variations on past events. Once a causal inference is made that force must be applied to the tree, by whatever means, then the invention of new ways to bring down apples can be imagined in the mind's eye and simulated in working memory. A machine that vibrates the branches automatically could be conceived and then tested in the mind before actually trying it out for real.

The left hemisphere is specialized for drawing multiple kinds of inferences.
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For example, when a split-brain patient is shown a picture of a pan and another picture of water, he can readily point with his right hand to a picture of boiling water. When this same kind of test is done with the right hemisphere and the left hand, the patient is unable to draw the simple inference that a pan and water go together to become a pan of boiling water. Similarly, syllogistic reasoning tasks also require inferences, and these recruit heavily the left hemisphere. For example, a verbal reasoning task might take the form of
all dogs are mammals; some mammals are large; therefore, some dogs are large
. Is this a valid conclusion? Neuroimaging of the left hemisphere reveals significant activity as the conclusion is evaluated. Even when a spatial reasoning task is presented instead of a language-based task, “the left still dominates in reasoning about those relations.”
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Recall that the right hemisphere is generally biased toward effectively processing visual-spatial information, so this involvement of the left in reasoning through the logic of spatial relations is telling.

Narrative and Language

The first tentative words of infancy turn into a torrent between the ages of eighteen and twenty-four months. This age range marks the shift from a single-word stage of language production to using two words, and it starts the child on a path to eventually uttering complete phrases and finally grammatical sentences. This skill in using language for communication with other human beings also eventually becomes the inner voice of the interpreter. However, in the early years, the child's interpreter speaks aloud in self-talk rather than silently. There is a slow transition in which the self-talk of the interpreter is vocalized just as if the child were speaking to her mother, brother, or friends. A young child in her preschool years can often be heard talking to herself aloud. The child is talking as if there were another person listening, but the speech is not intended for others. Rather, the speech is egocentric and intended for only the speaker to hear. As Lev Vygotsky concluded, “the child is thinking aloud, keeping up a running commentary, as it were, to whatever he may be doing.”
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This commentary eventually becomes interiorized around the time the child enters school, persisting as the inner voice of the interpreter.