Researchers from Germany have found that, contrary to popular belief, it's not just the right hemisphere of the brain that analyzes speech. The left hemisphere plays a role too.
Scientists previously assumed that while spoken words are picked up by the left side of the brain, they are analyzed on the right side. While the left side of the brain was believed to control motor functions, like making certain linguistic sounds, the right side was thought to decipher whether the sound was correct.
In this new research however, scientists measured the brain activity of speakers while talking with fMRI (functional magnetic resonance imaging) techniques to see which parts of the brain receive the most blood flow when speaking. In doing so, they found that both sides work together more than previously thought.
"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." says Dr. Chirtian Kell, one of the authors of the research.
One theory for this is that the left side of the brain is better at analyzing fast processes like the transition between sounds than the right side of the brain, which may be better at slower processes like analyzing a sound spectrum.
To test this theory out, Kell and his team set up an experiment in which they asked participants to tap with both hands to the rhythm of a metronome while recording their brain activity. In one test, they were asked to tap to each beat, and on another test, they were asked to tap once every four beats.
In the end, the researchers found that the participant's right hand was better at the quick tapping. This corresponded with the brain's left hemisphere (which controls the right side of the body) having more activity too. Meanwhile, the left hand tended to be better at tapping to the slower rhythm and corresponded to more activity in the right side of the brain.
Together, both studies demonstrate that hand motor function and speech are controlled by both sides of the brain, as opposed to just one. While the brain's left hemisphere is better suited for fast processes, its right hemisphere is better for slower processes.