The Making of the Mind: The Neuroscience of Human Nature (14 page)

Given these facts, scientists then turned to nonverbal forms of language and achieved considerable success relative to the early work by the Kelloggs. One project taught a chimpanzee named Washoe American Sign Language (ASL). By training Washoe to make the appropriate sign when shown a picture of an object, she was able to learn to express 132 different ASL signs and comprehend many more than that.
³¹
The expressive vocabulary learned by Washoe seemed to match reasonably closely with the words uttered by young human children. For example, Washoe learned to use a large number of category names, such as flower, fruit, and cat. In a different project, a bonobo named Kanzi learned how to choose visual symbols on a computer display called lexigrams. Each lexigram referred to a specific object or action. Kanzi learned from watching his caretakers point to each symbol appropriate to an object while speaking to him about “daily routines, events, and about comings and goings at the laboratory” and also about “trips to the woods to search for food, games of tickle and chase, trips to visit other primates at the laboratory, play with favorite toys such as balloons and balls, visits from friends, watching preferred TV shows, taking baths, helping pick up things, and other numerous simple activities characteristic of daily life.”
³²
By the age of six, Kanzi could identify 150 lexigram symbols on the computer when he heard the words
spoken to him; he could also perform correctly 70–80 percent of the time in comprehending and responding to novel sentences, such as “Put the rubber band on your ball” or “Bite the stick.”
³³
By way of comparison, a mother taught her human infant the lexigram board, along with the usual spoken language. It turned out that Kanzi did just as well, if not slightly better, than the child was doing at two years of age.

The findings of ape language learning were greeted with considerable skepticism, and they generated deep controversy. Arguments ensued regarding whether the hand signs or lexigrams were truly operating as symbols in the apes as they do in humans. Others contested whether the apes had knowledge of syntax in their comprehension of novel sentences or in their production of short sequences of signs. Certainly, it was apparent that their maximum vocabulary size was small and that their ability to produce novel expressions was highly limited. A hallmark of human language is its productivity—the ability to use a large but finite number of words to generate an infinite number of acceptable sentences. Against this standard, the apes fell far short. Their vocabularies are not just small; they also lack grammatical items and show no signs of sophisticated grammar such as embedded clauses.
³⁴

The divide between chimpanzees and humans in language capability should not be surprising. Chimpanzees have been evolving for approximately six million years since the last common ancestor hypothesized by evolutionary biologists. That there is any evidence at all of symbol use and semantic reference learned by chimpanzees in laboratories is surprising. So is the possibility that the alarm calls of monkeys are indeed primitive forms of semantic reference. Such findings hint at just how ancient the basis of semantics might be. What has become an exquisite system of symbolic thought and language use in modern humans may well have taken a very long time to develop. The adaptations that allow for the gift of language in humans are many and complex. That they were a long time in coming ought to be expected.

What, then, is known about the biological adaptations for language that are part of the human genome? With the exception of FOXP2, the genetic determinants of language remain unknown. But there must be other important genetic mechanisms yet to be discovered. For example, it is known that the brain develops specialized structures for the production and comprehension
of language. Most people are right handed, which means that the left hemisphere is considered dominant and contains a zone specialized for language. The language zone incorporates numerous brain structures in the left hemisphere, and damage to any of them can impair language use.

Among the most critical and best known are the following regions.
³⁵
Broca's area is located in the left frontal lobe and plays a critical role in the motor control of speech and in processing the syntax of a sentence. Damage to Broca's area causes difficulties with producing grammatical speech. Such injuries disrupt the ability to understand language when grammatical information is crucial. For example, “playing the field” and “the playing field” are one and the same to the right hemisphere. Without Broca's area, in the left hemisphere, the difference in meaning of these two phrases is lost. For a patient diagnosed with Broca's aphasia, a sentence such as “The boy kissed the girl” is difficult to interpret. Who was kissed? Without an intact Broca's region, the sentence cannot be correctly parsed to know that it was the girl who was kissed. Near Broca's area, only lower and a bit further forward, is a region that specializes in the phonological analysis of speech. Wernicke's area is located in the parietal lobe, near its boundary with the temporal lobe; it specializes in the comprehension of words. Patients with injuries to Wernicke's area have no trouble producing grammatically complex and highly fluent language. Their syntax is fine, but there is a problem in the semantics. Sentences, though fluent, can be vacuous in meaning or difficult to understand because of difficulties with the semantic reference of the words. At times, neologisms or made-up words are added. Finally, the left angular gyrus lies adjacent to Wernicke's area, a bit further back in the parietal lobe, near the occipital lobe. This region processes the visual features of written language, known as orthography, as opposed to the sound, or phonology, of language. Injuries to this area can disrupt reading and writing even though spoken language is unimpaired. The specific roles of genes, and the ways in which they interact with the social environment to produce such specialization of the left hemisphere for language, are still today unknown.

ORAL CULTURE

The monumental fact of history—indeed there would be no history if written language had never been invented—is that human beings alone ventured into a cultural world permeated by language. Our genes prepared us for an entirely new voyage of cultural evolution. The importance of this singularity of nature cannot be overstated. Although human beings have many distinctive features of body and mind, language stands out as the single most significant, for it lifted us into a realm of symbols and abstract thought. The civilizations of human history would never have been possible without the invention of language.

The Upper Paleolithic culture of early modern human beings was characterized by well-crafted stone tools. But it was the art that clearly documented the capacity of early modern humans for symbolic thought. Merlin Donald asked in
Origins of the Modern Mind
:

What sort of adaptation could possibly explain the explosion of tools, artifacts, and inventions of all sorts for all sorts of applications, and the eventual creation and maintenance of tribal political and social structures, which regulated everything from marriage to ownership, from justice to personal obligation. What change could have broken the constraints on mimetic culture, leading to the fast-moving exchanges of information found in early human culture? Speech and language are the obvious candidates to single out for these roles.
³⁶

The most important way that language altered the cultural landscape was not in the making of tools and weapons. Instead, it allowed the development of a richer social structure because people had a way to communicate their thoughts directly with others in the tribe. This greatly magnified the ability to transmit cultural knowledge from one generation to the next. Parents and elders could not only show the young, they could tell them. The culture became oral such that vast amounts of what a group knew could be told as narrative. What had happened in the past became known in the present through the power of language. By telling the stories of the past, the past could be preserved and its wisdom passed on to the next generation.

Before the invention of language, did our hominid ancestors communicate in some other way? If that were so, then could there still be some behavior of contemporary human beings that preserves this earlier mode? One intriguing candidate is the use of gestures and poses, the arts of nonverbal communication such as dance and mime. Through facial and other bodily expression human beings are certainly capable of nonverbal communication. Emotional states certainly can be very well communicated in this manner, but other states of mind can be shared among people, at least in a skeletal form, without the use of words. A mimetic form of culture—one based on bodily expression—may have preceded the invention of language and oral culture. It may have been an aspect of the culture of
Homo erectus
that today exists in the behavior of modern human beings as something of a cultural relic or fossil.
³⁷

Consider all the ways that a mimetic capacity is still with us. Dance is a powerful means to express feelings, and it can, with professional skill, do so in a highly sophisticated manner. A professional mime can communicate a complex sequence of events, accurately and often humorously, with nothing but adept bodily expression. Although we differ in skill and practice levels, each of us can pantomime to some extent when playing a game of charades. Stage and screen actors learn that their capacity to express emotions and thoughts through bodily expression is as important, if not more so, then their vocalizations.

On an everyday basis, human beings use body language to communicate their fears, hopes, and desires with one another. Our bodies speak to others, sometimes conveying the same message as our spoken words and other times belying them. These bodily expressions can be amorphous and not easily read across cultures, but the fact that they exist at all is the significant point here. By contrast, the facial expression of basic emotions is a universal form of human communication. The hand, arm, head, and eye gestures that often accompany human speech are particularly interesting in the way they help listeners to understand. They can convey some information about the speaker's thoughts that is left unspoken. Such gestures are thus part of the integrated system of communication.

Moreover, speech gestures also seem to help the speaker as well as the listener. The gestures represent some of what a speaker intends to say, thus
freeing working memory to concentrate on the thoughts that will be expressed through speech. Experiments have shown that when speakers spontaneously gesture while they talk, they are able to perform a second concurrent task better than when they choose not to gesture or are instructed not to gesture.
³⁸
The gestures that accompany speech reduce the load on working memory in much the same way as externalizing thoughts by writing them down. Put simply, spontaneous gesturing helps the speaker to think.

The power of gestures in human communication is seen most powerfully in deaf children. They are able to communicate successfully, even if they have not been exposed to sign language, by inventing iconic gestures that allow others to get the picture intended. These gestures, like those of American Sign Language and other formal nonspoken languages, assume “not only the function of language but also many of its formal features, such as segmentation (producing separate gestures to represent objects and the relations among them), combination (combining those gestures in a structured manner), and recursion (producing more than one proposition within a single gesture sentence).”
³⁹
The expression of thought through language erupts from the modern mind, as urgently through the hands as through the mouth.

Oral culture is the medium by which human beings have made sense of the world since the origin of the modern mind. It has provided the communal forum for the building of conceptual models—such as those of religion and science—and for the composing of stories regarding our identity, history, and destiny. What are we to make, then, of the human need to make sense of the world? Is the human drive for explanation simply a consequence of the invention of language and a product of oral culture? According to the ensemble hypothesis advanced here, there is more than just language at work in this drive. It was instead a capacity to narrate events as inner speech and infer the causes of those events that lies behind the human drive to interpret all that happens to us.

As useful as language is for communicating with others, it is also a means for silent thinking and internal dialogue. Human consciousness is unique from that of any other species because we can talk to ourselves. The mind spins a yarn that explains to us, through the voice of inner speech, our experiences in the world. This inner story telling or narrator is known in the scientific literature as the interpreter of conscious experience, and it has been shown to reside in the left cerebral hemisphere of the brain.

The discovery of the interpreter began with the famous split-brain research of Michael Gazzaniga and his colleagues. They studied epileptic patients whose severe seizures, uncontrolled by medications, were successfully treated by surgically separating the two cerebral hemispheres. Neurosurgeons cut the fibers of the corpus callosum, a massive band of fibers in the interior of the brain that connects the left hemisphere with the right hemisphere, with the aim of stopping the electrical storm of haphazard neural firings underlying the seizure. Not only did the operation work, the patients appeared to show no adverse side effects, at least as detectible in everyday cognitive functioning. In special laboratory tests specifically designed to reveal the left and right hemispheres functioning independently of each other, some remarkable findings emerged.

In a typical experiment, the patient was seated in front of a screen onto which words were projected briefly.
¹
Each trial began with the individual being told to fixate his or her gaze on the dot projected in the center of the screen. Next, a word was flashed for only a tenth of second or so either to
the left of the dot or to the right. The researchers capitalized on the fact that all stimuli in our left visual field are processed first by the right hemisphere before being sent via the corpus callosum to the left hemisphere. Conversely, in a normal participant, any word presented in the right visual field is first perceived by the left hemisphere. In the case of the split-brain patient, what entered the right hemisphere stayed in the right hemisphere, having no easy means of transit. The same was true for a word perceived only by the left hemisphere because the corpus callosum had been severed.

When the word
ring
was flashed on the right, the left hemisphere was able to recognize the object and to name it promptly using its language capacity. On the other hand, when the word
key
was flashed to the left hemisphere, the patient said nothing. If pressed as to what word had been presented, the patient said “I don't know.” The right hemisphere, though, is known to possess the capacity to recognize objects. It is in fact highly skilled at the task of perceiving objects in a holistic, rapid manner. Was it possible, then, that the right hemisphere knew more than it could say?

The researchers tested for the unspoken wisdom of the right brain by asking the patient to reach under the projection screen and pick up, one at time, several objects. These test objects could be felt but not seen. As it happened, the patient was easily able to pick out the correct object, in this case a key, if and only if he or she used the left hand, which is under the control of the sensory-motor cortex in the right hemisphere. In other words, the knowledge that the right hemisphere had the object could be expressed through the hand's privileged access to that knowledge. The speech systems of the left hemisphere were in the dark. Particularly compelling, so were the sensory-motor systems of the right hand, mediated as they are by left hemisphere.

Here, then, was an astonishing discovery. It flies in the face of the fact that our phenomenal experience of consciousness is unitary. Attention binds together different streams of information processing, including those initiated within the left hemisphere and those of the right. With the corpus callosum intact, we are normally unaware of the independent contribution of each hemisphere. Yet the split-brain findings showed that the consciousness of the human left cerebral hemisphere could operate independently of the right hemisphere, at least in patients for whom the normal connections
between hemispheres were surgically severed for reasons of medical necessity. The split-brain studies prompted thousands of experiments on normal individuals with intact communication between the left and right hemisphere by measuring brain wave activity and employing other techniques of cognitive science. Brain waves refer to the fluctuations in microvoltage that emanate from the skull as a consequence of neural activity in underlying regions of the brain. They can be detected using an electroencephalograph (EEG) that monitors changes from as many as 128 electrodes positioned all over the skull. The EEG signal picked up from a specific electrode is generated by a population of neurons in an area several millimeters in diameter. The signals generated from a small region of cortex can be accurately measured from millisecond to millisecond through EEG recordings.

Other important discoveries followed regarding the propensity of one hemisphere to be biased in favor of processing particular kinds of analysis.
²
For example, the left hemisphere is biased toward processing language, whereas the right hemisphere is biased toward visual-spatial tasks. The left hemisphere is better inclined to cope with tasks that call for sequential, analytical, logical reasoning, whereas the right hemisphere prefers tasks that benefit from simultaneous, holistic, intuitive judgments. The notion of the left as the rational brain and the right as the creative brain morphed into a pop culture, cartoon version of the scientific facts on hemispheric differences: to become more creative, one should think only with the right brain. The reality is that the brain acts in concert, as a whole, with each hemisphere simply biased toward greater efficiency in one domain over another. Indeed, it is only when the connections between the two hemispheres are severed that one can begin to see the specialized character of right versus left processing. More on point, one cannot turn off the left brain in order to turn on the right brain, nor would one want to do that, giving up fully half of the brain's computational power. To do so is like telling the right half of the orchestra to play while silencing the left.

THE INTERPRETER OF THE LEFT HEMISPHERE

As famous and influential as the split-brain research became in popular culture, the most significant discovery of them all escaped the notice of the public eye, namely that the left hemisphere serves as an interpreter of the conscious experiences of the brain's cerebral hemispheres. It seeks an explanation of why events occur and concocts a story of the causal relations involved. The left hemisphere uses its linguistic capacity to narrate why such and such occurred. The familiar inner voice that is such an intimate part of the self is the left hemisphere going about its work of commentary and explanation. In Michael Gazzaniga's words, “The interpreter, the last device in the information chain in our brain, reconstructs the brain events and in doing so makes telling errors of perception, memory, and judgment.”
³

To illustrate the interpreter, suppose a command “Take a walk” is flashed in the left visual field to the mute right hemisphere of a male split-brain patient. Although the patient is unaware of seeing the words, he will respond to the command, push back his chair from the table, and get up and walk. Michael Gazzaniga explained:

You ask “Why are you doing that?” The subject replies, “Oh, I need to get a drink.” The left brain doesn't know why it finds the body leaving the room. When asked, it cooks up an explanation.
⁴

In a clever experiment designed to catch the interpreter in the act of spinning an explanation, Gazzaniga and his colleagues simultaneously presented a scene of a snowman and a snow covered house to the left visual field and a chicken claw to the right visual field.
⁵
The patient then pointed with the left hand to one of four test pictures (shovel, lawn mower, rake, pick) that was most appropriate to what had been seen by the right hemisphere (the snow scene). The left hand, controlled by the right hemisphere, was easily able to point to the shovel. In the same manner, when the patient pointed with his right hand to the most appropriate of four choices (toaster, rooster, apple, hammer), it picked out the rooster, what had been registered only in the left hemisphere.
The experimenter then asked the patient why the left hand was pointing to the shovel. Because the right hemisphere is mute, the left hemisphere interpreter had to take charge to respond. Because the interpreter did not know why the right hemisphere picked the shovel with the left hand, it made up a story that fit with its conscious experience of the moment. The interpreter said the right hemisphere selected the shovel to clean out the chicken shed!

In a similar test, a split-brain patient registered the word “bell” in the right hemisphere and “music” in the left. Again, selecting from a set of test pictures, the right hemisphere selected a picture of a bell. When asked why, the interpreter of the left hemisphere concocted a reason that incorporated the information of which it was currently aware: “Music—last time I heard any music was from the bells outside here, banging away,” making reference to the bells ringing from Dartmouth library.
⁶

The left hemisphere attempts to make sense of the emotional contents of the right hemisphere as well as its cognitive contents. Experimenters presented an emotionally positive stimulus selectively to the right hemisphere, as a means of inducing a positive mood shift within that half of the brain. The left hemisphere begins to interpret its current experience in a positive way, too. What was described moments before as a neutral experience by the interpreter is now reassessed as a positive emotional experience—in this way the sudden shift in the emotional state of the right hemisphere is made sense of by the left's interpreter.
⁷
In a converse situation, when the right hemisphere is shifted to a negative mood, the left hemisphere now expresses negative feelings instead of what had just been neutral.

Another example of the left hemisphere interpreter can be seen in hypothesis testing. The interpreter seeks explanations for events by formulating and testing hypotheses. Just as a scientist uses hypotheses to explain observations of the world, the left hemisphere does the same to explain its current conscious experience. Consider a test in which a light comes on either at the top or the bottom of a screen on a series of trials. On some trials, a small green screen appears at the top of the screen, while on other trials a small red square appears at the bottom. The participant in the experiment attempts to predict whether on the next trial the light will come on at the top or at the bottom. The prediction is made by pushing a button labeled
top
or one labeled
bottom
.
To test split-brain patients, the lights were flashed to the right visual field and the right hand was used to respond—this assessed the left hemisphere's performance of the task. Or, alternatively, the lights were flashed to left visual field and the left hand was used to respond in order to tap how the right hemisphere performed the task.

In this task, the actual sequence of lights is determined randomly, except that the probabilities of the light appearing at the top versus the bottom are not 50 percent each. Instead, the task is biased so that the top light comes on 60 percent of the time and the bottom light 40 percent of the time. To make the most correct predictions, the optimal strategy would be to guess the most probable response—the top light—every time. That way, it is certain that the prediction would be correct 60 percent of the time—one would maximize performance following such a simple strategy. In split-brain patients, when the task is presented to the right hemisphere, the choices made generally come close to the maximizing strategy.
⁸
In other words, the right hemisphere is able to perform the task in a manner that comes close to optimal guessing.

The left hemisphere interpreter, however, tries out all sorts of hypotheses about the sequence of lights seen in the past. It assumes there is some underlying explanation for why the lights occur in the order they do and sets about trying to figure out the pattern. As a consequence, the left hemisphere fails to take advantage of the simple strategy of picking the most probable outcome most of the time. Instead, it tries to figure out a rule that explains the pattern underlying the distribution of 60 percent top light and 40 percent bottom light. For example, the interpreter of the left hemisphere might hypothesize that the sequence for five lights is top, top, bottom, top, and bottom. Such a hypothesis is incorrect, since the lights come on at random, with the only constraint that the top light comes on 60 percent of the time. It could have just as easily been bottom, bottom, top, top, and top, which would still fit the 60 percent top rule. Hypothesis testing will inevitably lead to erroneous predictions, because the actual sequence is random. The key point is that the left hemisphere performs worse than the right hemisphere because the interpreter leads to complicated hypotheses that fail.
⁹
Normal participants in whom the corpus callosum is intact make the same mistake; they, too, come up with elaborate explanations of when the top or bottom light will appear, convinced
that they have discovered a pattern in what is random. In the normal human brain, then, the dominant left hemisphere overrules the passive, but in a sense brighter, right hemisphere. Ironically, then, the normal subjects make more mistakes in the task than the left hand of the split-brain subject.