How the brain controls our speech

Date:
June 10, 2020
Source:
Goethe University Frankfurt
Summary:
Speaking requires both sides of the brain. Each hemisphere takes
over a part of the complex task of forming sounds, modulating the
voice and monitoring what has been said. However, the distribution
of tasks is different than has been thought up to now, as an
interdisciplinary team of neuroscientists and phoneticians has
discovered.



FULL STORY ========================================================================== Speaking requires both sides of the brain. Each hemisphere takes over
a part of the complex task of forming sounds, modulating the voice and monitoring what has been said. However, the distribution of tasks is
different than has been thought up to now, as an interdisciplinary team
of neuroscientists and phoneticians at Goethe University Frankfurt and
the Leibniz-Centre General Linguistics Berlin has discovered: it is
not just the right hemisphere that analyses how we speak -- the left
hemisphere also plays a role.


========================================================================== Until now, it has been assumed that the spoken word arises in left side
of the brain and is analysed by the right side. According to accepted
doctrine, this means that when we learn to speak English and for example practice the sound equivalent to "th," the left side of the brain controls
the motor function of the articulators like the tongue, while the right
side analyses whether the produced sound actually sounds as we intended.

The division of labour actually follows different principles, as Dr
Christian Kell from the Department of Neurology at Goethe University
explains: "While the left side of the brain controls temporal aspects
such as the transition between speech sounds, the right hemisphere
is responsible for the control of the sound spectrum. When you say
'mother', for example, the left hemisphere primarily controls the dynamic transitions between "th" and the vowels, while the right hemisphere
primarily controls the sounds themselves." His team, together with the phonetician Dr Susanne Fuchs, was able to demonstrate this division of
labour in temporal and spectral control of speech for the first time
in studies in which speakers were required to talk while their brain
activities were recorded using functional magnetic resonance imaging.

A possible explanation for this division of labour between the two
sides of the brain is that the left hemisphere generally analyses fast processes such as the transition between speech sounds better than the
right hemisphere. The right hemisphere could be better at controlling the slower processes required for analysing the sound spectrum. A previous
study on hand motor function that was published in the scientific
publication "elife" demonstrates that this is in fact the case. Kell
and his team wanted to learn why the right hand was preferentially used
for the control of fast actions and the left hand preferred for slow
actions. For example, when cutting bread, the right hand is used to
slice with the knife while the left hand holds the bread.

In the experiment, scientists had right-handed test persons tap with both
hands to the rhythm of a metronome. In one version they were supposed
to tap with each beat, and in another only with every fourth beat. As
it turned out, the right hand was more precise during the quick tapping sequence and the left hemisphere, which controls the right side of the
body, exhibited increased activity. Conversely, tapping with the left
hand corresponded better with the slower rhythm and resulted in the
right hemisphere exhibiting increased activity.

Taken together, the two studies create a convincing picture of how complex behaviour -- hand motor functions and speech -- are controlled by both
cerebral hemispheres. The left side of the brain has a preference for
the control of fast processes while the right side tends to control the
slower processes in parallel.


========================================================================== Story Source: Materials provided by Goethe_University_Frankfurt. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mareike Floegel, Susanne Fuchs, Christian A. Kell. Differential
contributions of the two cerebral hemispheres to temporal and
spectral speech feedback control. Nature Communications, 2020; 11
(1) DOI: 10.1038/s41467-020-16743-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200610094042.htm

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