How the brain processes sign language
Date:
February 19, 2021
Source:
Max Planck Institute for Human Cognitive and Brain Sciences
Summary:
Over 70 million deaf people use sign languages as their preferred
communication form. Although they access similar brain structures
as spoken languages, it hasn't been identified the brain regions
that process both forms of language equally. Scientists have now
discovered that Broca's area in the left hemisphere, central for
spoken languages, is also crucial for sign languages. This is where
the grammar and meaning are processed, regardless of whether it
is spoken or signed language.
FULL STORY ==========================================================================
The ability to speak is one of the essential characteristics that
distinguishes humans from other animals. Many people would probably
intuitively equate speech and language. However, cognitive science
research on sign languages since the 1960s paints a different picture:
Today it is clear, sign languages are fully autonomous languages and have
a complex organization on several linguistic levels such as grammar and meaning. Previous studies on the processing of sign language in the human
brain had already found some similarities and also differences between
sign languages and spoken languages. Until now, however, it has been
difficult to derive a consistent picture of how both forms of language
are processed in the brain.
========================================================================== Researchers at the MPI CBS now wanted to know which brain regions are
actually involved in the processing of sign language across different
studies -- and how large the overlap is with brain regions that hearing
people use for spoken language processing. In a meta-study recently
published in the journal Human Brain Mapping, they pooled data from sign language processing experiments conducted around the world. "A meta-study
gives us the opportunity to get an overall picture of the neural basis of
sign language. So, for the first time, we were able to statistically and robustly identify the brain regions that were involved in sign language processing across all studies," explains Emiliano Zaccarella, last author
of the paper and group leader in the Department of Neuropsychology at
the MPI CBS.
The researchers found that especially the so-called Broca's area in
the frontal brain of the left hemisphere is one of the regions that
was involved in the processing of sign language in almost every study evaluated. This brain region has long been known to play a central
role in spoken language, where it is used for grammar and meaning. In
order to better classify their results from the current meta-study, the scientists compared their findings with a database containing several
thousand studies with brain scans.
The Leipzig-based researchers were indeed able to confirm that there
is an overlap between spoken and signed language in Broca's area. They
also succeeded in showing the role played by the right frontal brain
-- the counterpart to Broca's area on the left side of the brain. This
also appeared repeatedly in many of the sign language studies evaluated, because it processes non- linguistic aspects such as spatial or social information of its counterpart.
This means that movements of the hands, face and body -- of which signs
consist -- are in principle perceived similarly by deaf and hearing
people. Only in the case of deaf people, however, do they additionally
activate the language network in the left hemisphere of the brain,
including Broca's area. They therefore perceive the gestures as gestures
with linguistic content -- instead of as pure movement sequences, as
would be the case with hearing people.
The results demonstrate that Broca's area in the left hemisphere is a
central node in the language network of the human brain. Depending on
whether people use language in the form of signs, sounds or writing,
it works together with other networks. Broca's area thus processes not
only spoken and written language, as has been known up to now, but also abstract linguistic information in any form of language in general. "The
brain is therefore specialized in language per se, not in speaking,"
explains Patrick C. Trettenbrein, first author of the publication and
doctoral student at the MPI CBS. In a follow-up study, the research team
now aims to find out whether the different parts of Broca's area are
also specialized in either the meaning or the grammar of sign language
in deaf people, similar to hearing people.
========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Human_Cognitive_and_Brain Sciences. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. Patrick C. Trettenbrein, Giorgio Papitto, Angela D. Friederici,
Emiliano
Zaccarella. Functional neuroanatomy of language without speech:
An ALE meta‐analysis of sign language. Human Brain Mapping,
2020; 42 (3): 699 DOI: 10.1002/hbm.25254 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/02/210219124236.htm
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