How human species are special
How human species are special
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
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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