Outside of the laboratory
settings one rarely encounters situations where one would have to try to understand
discourse without contextual information. When those instances do take place,
it is often difficult to comprehend until one gets clues on the relevant
context; on the other hand, with the appropriate context provided, it is often
very easy to predict what another is about to say, even if the information that is provided per se would be rather limited. The contextual cues can further be broken down
to local and global; when listening to narrated stories or discourse,
the one or two preceding sentences are though to provide the local context,
whereas the preceding paragraph typically is thought to provide the global context that
guides comprehension. The underlying neural mechanisms have, however, remained
largely unexplored, with some cognitive theories speculating that availability
of local and global contextual information in working memory would be the
determining factor.
In their recent study Egidi and
Caramazza (2013) probed, by combining behavioral measures and functional
magnetic resonance imaging in healthy volunteers, the neural structures
supporting integration of narrative information by local and global contextual
information. They specifically used short stories where the endings were
consistent vs. inconsistent with the global vs. local context, set up
by distally vs. proximally preceding sentences. Thirty subjects first
participated in a self-paced reading task where they were instructed to move to
the next sentence only when they had comprehended the one at hand. The subjects read locally consistent sentences
quicker, but slower when the sentences were globally inconsistent, and vice versa, thus demonstrating robust
behavioral interaction effects. Fourteen subjects took part in the functional magnetic
resonance imaging study that disclosed involvement of three different networks
of brain areas, one comprising superior parietal areas and intraparietal sulcus
associated with integration of story endings with both local and global
contextual information, one that consisted of supramarginal gyrus, superior
parietal lobule, and anterior intraparietal sulcus sensitive to availability of
global context, and a third one comprising of multiple areas that was associated with fluency of the
processing given the local context.
These results are highly exciting
in that they illuminate how global and immediate/local contextual information
is integrated by the brain to facilitate comprehension. The setup and findings of
the authors provide interesting possibilities for further neuroimaging research
on this very important topic that is one of the most fundamental research questions concerning human language comprehension. After all, language comprehension is a process
that to a large degree relies on (and in case of misinterpretations is biased by) preceding contextual
information. Understanding the underlying neural mechanism provides
important insights as to how contextually-driven language comprehension is possible.
Reference: Egidi G, Caramazza A. Cortical systems for local and
global integration in discourse comprehension, NeuroImage (2013), advance
online publication prior to print. http://dx.doi.org/10.1016/j.neuroimage.2013.01.003
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