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Abstract:
Most linguistics textbooks present a rather simple picture of
the representation of language processing in the brain, involving
two areas, Broca's area (left inferior frontal lobe) and Wernicke's
area (left posterior temporal lobe), and the connection between
them (arcuate fasciculus). Versions of this model have been around
since the end of the 19th century (Wernicke and Lichtheim).
In this paper we want to discuss a number of experiments looking
at the comprehension of sentences of different degrees of
complexity, making use of neuroimaging techniques, more
specifically positron emission tomography (PET) and functional
magnetic resonance imaging (fMRI), which cast serious doubt on the
correctness of the generally accepted picture. The following issues
will be discussed:
- The functions of the two traditionally distinguished language
areas are not as clear-cut as is usually assumed, i.e. Broca's area
underlying syntax and Wernicke's area underlying semantics. Broca's
area, for instance, becomes activated when subjects read word lists
as well as when they read complex sentences.
- There is evidence that more than just these two areas in the
left hemisphere are involved in language comprehension. The
anterior temporal lobe, for instance, is more highly activated when
subjects read sentences than when they read word lists, indicating
that it supports sentence comprehension.
- It will be shown that areas in the right hemisphere,
especially the right frontal lobe, and also the cerebellum are
involved in language processing in addition to left hemisphere
areas. The right frontal lobe, for instance, is activated when
subjects have to read sentences which contain a lexically ambiguous
word that is disambiguated to the non-preferred interpretation
later in the sentence.
- Language processing shares components with several
non-linguistic cognitive systems, necessitating a revision of the
notion of modularity. A comparison of subject and object relative
clauses, for instance, shows that the visual cortex is more
activated in the latter than the former; the same area has been
shown to be active in visual attention tasks. This suggests that
the language module is not completely informationally encapsulated:
some information internal to the language 'module' is available to
affect processes in other cognitive 'modules'.
In conclusion, the function of a number of traditional language
areas in the brain has to be re-evaluated; moreover, a number of
additional areas, both in the left and the right hemisphere have
been shown to be active in language understanding. As a result of
these findings, the 'language module' must be conceived of as a
much more complex network of functionally specialized areas than
has traditionally been assumed in linguistics; some of these areas
may interact with other cognitively specialized areas/networks.
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