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. 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,
sometimes produce grammatical but meaningless speech. Another
kind of aphasias is conduction aphasia; in this condition, patients suffer difficulty
in repeating speech and have problems producing spontaneous speech.
Conduction aphasia is sometimes associated with damage to the parietal regions
shown in Figure 12.1.
Although the importance of these left-cortical areas to speech is well documented
and there are many well-studied cases of aphasia resulting from damage
in these regions, it has become increasingly apparent that there is no simple
mapping of damaged areas onto types of aphasia. Current research has focused
on more detailed analyses of the deficits and of the regions damaged in each
Although there is much to understand, it is a fact that human evolution and
development have selected certain left-cortical regions as the preferred locations
for language. It is not the case, however, that language has to be left lateralized.
There are those left-handers who have language in the right hemisphere, and
young children who suffer left-brain damage may develop language in the right
hemisphere, in regions that are homologous to those depicted in Figure 12.1 for
the left hemisphere.
Language is preferentially localized in the left hemisphere in prefrontal
regions (Broca’s area), temporal regions (Wernicke’s area), and parietal
regions (supramarginal and angular gyri).
•The Field of Linguistics
The academic field of linguistics attempts to characterize the nature of language.
It is distinct from psychology in that it studies the structure of natural
languages rather than the way in which people process natural languages.
Despite this difference, the work from linguistics has been extremely influential
in the psychology of language. As we will see, concepts from linguistics play
an important role in theories of language processing. As noted in Chapter 1, the
influence from linguistics was important to the decline of behaviorism and the
rise of modern cognitive psychology