Fluctuation is variation. The term fluctuation indicates changes or disturbances in the output of the human voice. It is a significant change indicating the voice is unstable. Although the difference in voicing is desirable artistically such as singing, too much variability leads to speech that is unintelligible. Verbal change is also indicative of lying which includes more pauses, slower speech, stuttering, and an elevation in pitch. Humans are the only primates who can control the pitch of our voices, and this pitch is crucial as it can convey information regarding our mood, words of emphasis, and even whether a sentence is a declaration or a question. Scientists at the University of California are now researching what area of the brain controls our ability to alter our speech.
The research seeks to pioneer advanced brain prosthetics that allow those who can’t speak to express themselves in natural ways. This research demonstrates that although one part of the brain causes the lip, tongue, and throat muscles to work in unison to form combinations of vowels and consonants to create the phonetic sounds of speech, a different region of the brain works independently to control speech fluctuations.
To fully understand how the brain can control speech, an understanding of what is happening in the brain in real time while someone is speaking is needed. The activity occurring in the brain is an understanding of brain function beyond just where speech functions localize in the brain. More critical to the research is understanding how the cells of the brain encode command indicators for throat and mouth muscles to form speech.
Volunteers modulated changes in pitch to emphasize different words in a sentence. The volunteers read sentences multiple times, and each time they emphasized different words which changed the meaning of the sentence subtly. This procedure allows the research team to look at the differences in brain activity depending upon how the speakers emphasized different words by changing pitch and not altering the words of the sentence. Neurons in adjacent areas activate when speakers change the overall pitch of their voice.
The team notes that activation of neurons in an area of the brain known as the dorsal laryngeal motor cortex is linked to changes in pitch when a variety of words within a sentence receive emphasis. As this area of the cortex activates, the higher a speaker’s pitch on individual words will be. This finding was present when the volunteers were speaking and when the patients sang a simple song.
The research group is already working on their next project which involves reverse engineering the way the brain controls pitch. In other words, can a word being emphasized be predicted by looking at the neural activity? The researchers hope this research may lead to a speech prosthetic that could provide a naturalistic voice to those who are not in possession of one. It will be fascinating seeing what other surprises the brain has in store for us.