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The most fundamental biological fact about language is that it is stored
in the brain, and, more importantly, that language function is localized
in particular areas of the brain. This is hardly a new idea, going back at
least to Franz Joseph Gall, the eighteenth-century neuroanatomist who
developed the field of phrenology. Gall believed that various abilities
such as wisdom, musical ability, morality, and language, were located
in different areas of the brain and could be discovered by feeling bumps
on a person's skull. Gall was, of course, wrong about the bumps, but it
seems to be true that some neurally based abilities, such as language,
have specific locations in the brain. The first conclusive demonstration
that language was localized in the brain took place in 1861 when a
French neurologist named Paul Broca presented to the Paris
Anthropological Society the first case of aphasia (Dingwall 1993).
Aphasia is 2 language impairment linked to a brain lesion. Broca had a
patient who had received a blow to the head with the result that he
could not speak beyond uttering Tan, Tan, and, thus, Broca called him
Tan-Tan. Upon autopsy, he was found to have a lesion in the frontal
lobe of the left hemisphere of his brain. Ten years later a German neu-
rologist named Carl Wernicke reported a different kind of aphasia, one
characterized by fluent but incomprehensible speech (Dingwall 1993)
Wernicke's patient was found to also have a left hemisphere lesion, far-
ther back in the temporal lobe. Neurolinguistics is the study of the rep-
resentation of language in the brain, and the discovery of aphasias led
to the birth of this interdisciplinary field.The two predominant kinds of aphasia are still called by the names of
the men who first described them, as are the areas of the brain associ-
ated with each. Broca's aphasia, also known as non-fluent aphasia, is
characterized by halting, effortful speech; it is associated with damage
involving Broca's area in the frontal lobe of the left hemisphere
Wernicke's aphasia, also called fluent aphasia, is characterized by fluent
meaningless strings; it is caused by damage involving Wernicke's area in the temporal lobe of the left hemisphere. These two kinds of aphasias.
among others, differ markedly in terms of the grammatical organiza-
tion of the patient's speech. The speech associated with Broca's aphasia
has been characterized as agrammatic; it consists of primarily content
words, lacking syntactic and morphological structure. In contrast, the
speech of people with Wernicke's aphasia has stretches of grammati-
cally organized clauses and phrases, but it tends to be incoherent and
meaningless. In conversation, it appears that people with Broca's apha-
sia comprehend what is said to them, while people with Wernicke's
aphasia do not. Thus, a general clinical characterization has been that
people with Broca's aphasia have more of a problem with speech pro-
duction than with auditory comprehension, whereas people with
Wernicke's aphasia produce fluent and well-articulated but meaning-
less speech, and have problems with auditory comprehension.
Psycholinguists studying the comprehension abilities of people
with Broca's aphasia discovered something very interesting. People
with Broca's aphasia had no difficulty in understanding sentences
like (3a), but had difficulty with sentences like (3b) (Caramazza and
Zurif 1976):

a. The apple the boy is eating is red.
b.
The girl the boy is chasing is tall.
Both sentences are constructed of common words; both sentences also
have identical structures, including a relative clause modifying the sub-
ject noun. There is, however, a profound difference between them: real-
world knowledge allows a person to successfully guess the meaning of
(3a), but not (3b). Comprehension of (3b) requires an intact syntactic
processing system. Caramazza and Zurif's result suggests an explanation
as to why people with Broca's aphasia seem to have little trouble with
comprehension in conversational contexts. People with aphasia compen-
sate for their impaired grammatical processing system by using real-
world knowledge to figure out the meanings of sentences in discourse. In
ordinary conversation with people one knows well and with whom one
shares a great deal of real-world knowledge one can understand much of
what is said without having to do a full analysis of sentence structure.
The question remains, of course, as to whether the grammatical problems
of people with aphasia are a result of an impaired linguistic competence
or are the result of difficulty in using that competence to produce and
understand speech. It is very difficult to answer this question experimen-
tally, but some researchers have found people with agrammatic aphasia
whose metalinguistic skills with respect to syntax are better than their ability to produce syntactically complex sentences (Linebarger, Schwartz,
and Saffran 1983). This would suggest that the performance system is
more impaired than the underlying grammar.
Figure 3.1 provides a sketch of the left hemisphere of the cortex of
the brain, with Broca's and Wernicke's areas indicated. Broca's area is
located near the motor area of the cortex, while Wernicke's is near the
auditory area. Importantly, despite the proximity of these areas to motor
and auditory areas, aphasias are purely linked to language, and not to
motor abilities or audition. Users of signed languages can also become
aphasic if they experience damage to the relevant areas in the left hemi-
sphere. Their signs are non-fluent, halting, and agrammatic. This is
true, despite the fact that they have no motor disability in their hands
and can use them in everyday tasks with no difficulty (Poizner, Klima,
and Bellugi 1987). The fact that signers become aphasic is dramatic con-
firmation of the fact that signed languages not only have all the formal
properties of spoken language, but are similarly represented in the
brain. It also demonstrates that the neurological damage that produces
aphasia impairs language systems, rather than motor systems.Aphasia is not a simple or clear-cut disorder. There are many different
kinds of aphasia in addition to those classified as fluent and non-fluent,
and many different behaviors that characterize the various clinical
types of aphasia. Furthermore, much more of the left hemisphere is
involved with language than just Broca's and Wernicke's areas; the area
all along the Sylvian fissure, deep into the cortex, is associated with
language function. Consequently, the localization of the damage for
Broca's or Wernicke's patients does not always neatly correspond with
the classical description (De Bleser 1988; Willmes and Poeck 1993).
People with aphasia differ greatly in the severity of their symptoms,
ranging from mild impairment to a global aphasia where ali four lan-
guage modalities - auditory and reading comprehension, and oral and
written expression - are severely impaired.