How human species are special

How human species are special

Language Structure

What makes the human species special? There are two basic hypotheses about

why people are intellectually different from other species. In the past few chapters,

I indulged my favorite theory, which is that we have unmatched abilities to solve

problems and reason about our world, owing in large part to the enormous development

of our prefrontal cortices. However, there is another theory at least as popular in cognitive

science, which is that humans are special because they alone possess a language.

This chapter and the next will analyze in more detail what language is, how people

process language, and what makes human language so special. This chapter will focus

primarily on the nature of language in general, whereas the next chapter will contain

more detailed analyses of how language is processed. We will consider some of the

basic linguistic ideas about the structure of language and evidence for the psychological

reality of these ideas, as well as research and speculation about the relation between

language and thought. We will also look at the research on language acquisition. Much

of the evidence both for and against claims about the uniqueness of human language

comes from research on the way in which children learn the structure of language.

In this chapter, we will answer the questions: • What does the field of linguistics tell us about how language is processed? • What distinguishes human language from the communication systems of other

species? • How does language influence the nature of human thought? • How are children able to acquire a language?

•Language and the Brain

The human brain has features strongly associated with language. For almost all

of the 92% of people who are right-handed, language is strongly lateralized in

the left hemisphere. About half of the 8% of people who are left-handed still

have language left lateralized. So 96% of the population has language largely

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in the left hemisphere. Findings from studies with split-brain patients (see

Chapter 1) have indicated that the right hemisphere has only the most rudimentary

language abilities. It was once thought that the left hemisphere was

larger, particularly in areas taking part in language processing, and that this

greater size accounted for the greater linguistic abilities associated with the left

hemisphere. However, neuroimaging techniques have suggested that the differences

in size are negligible, and researchers are now looking to see whether

there are differences in neural connectivity or organization (Gazzaniga, Ivry, &

Mangun, 2002) in the left hemisphere. It remains largely a mystery what differences

between the left and the right hemispheres could account for why language

is so strongly left lateralized.

Certain regions of the left hemisphere are specialized for language, and

these are illustrated in Figure 12.1. These areas were initially identified in studies

of patients who suffered aphasias (losses of language function) as a consequence

of stroke. The first such area was discovered by Paul Broca, the French surgeon

who, in 1861, examined the brain of such a patient after the patient’s death (the

brain is still preserved in a Paris museum). This patient was basically incapable

of spoken speech, although he understood much of what was spoken to him.

He had a large region of damage in a prefrontal area that came to be known

as Broca’s area. As can be seen in Figure 12.1, it is next to the motor region that

controls the mouth. Shortly thereafter, Carl Wernicke, a German physician,

identified patients with severe deficits in understanding speech who had damage

in a region in the superior temporal cortex posterior to the primary auditory

cortex. This area came to be known as Wernicke’s area. Parietal regions

close to Wernicke’s area (the supramarginal gyrus and angular gyrus) also have

also been found to be important to language.

Two of the classic aphasias, now known as Broca’s aphasia and Wernicke’s

aphasia, are associated with damage to these two regions. Chapter 1 gave

Brain Structures

Broca’s area

Wernicke’s area

Supramarginal gyrus

Angular gyrus

Motor face area

Primary auditory area

FIGURE 12.1 A lateral view of

the left hemisphere. Some of

the brain areas implicated in

language are in boldface type.

(From Dronkers, Redfern, & Knight, 2000.)

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examples of the kinds of speech problems suffered by patients with these two

aphasias. The severity of the damage determines whether patients with Broca’s

aphasia will be unable to generate almost any speech (like Broca’s original

patient) or be capable of generating meaningful but ungrammatical speech.

Patients with Wernicke’s aphasia, in addition to having problems with comprehension,

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