Evolution and humans: our speech is highly complex (Evolution)

by David Turell , Saturday, June 02, 2018, 00:24 (2365 days ago) @ David Turell

It requires around 100 muscles and several parts of a coordinated brain to control it all:

https://www.sciencedaily.com/releases/2018/06/180601134731.htm

"When we speak, we engage nearly 100 muscles, continuously moving our lips, jaw, tongue, and throat to shape our breath into the fluent sequences of sounds that form our words and sentences. A new study reveals how these complex articulatory movements are coordinated in the brain.

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"The new research reveals that the brain's speech centers are organized more according to the physical needs of the vocal tract as it produces speech than by how the speech sounds (its "phonetics"). Linguists divide speech into abstract units of sound called "phonemes" and consider the /k/ sound in "keep" the same as the /k/ in "coop." But in reality, your mouth forms the sound differently in these two words to prepare for the different vowels that follow, and this physical distinction now appears to be more important to the brain regions responsible for producing speech than the theoretical sameness of the phoneme.

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"In the new study, Chartier and Anumanchipalli asked five volunteers awaiting surgery, with ECoG electrodes placed over a region of ventral sensorimotor cortex that is a key center of speech production, to read aloud a collection of 460 natural sentences. The sentences were expressly constructed to encapsulate nearly all the possible articulatory contexts in American English. This comprehensiveness was crucial to capture the complete range of "coarticulation," the blending of phonemes that is essential to natural speech.

"'Without coarticulation, our speech would be blocky and segmented to the point where we couldn't really understand it," said Chartier.

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"The experiments revealed that a remarkable diversity of different movements were encoded by neurons surrounding individual electrodes. The researchers found there were four emergent groups of neurons that appeared to be responsible for coordinating movements of muscles of the lips, tongue, and throat into the four main configurations of the vocal tract used in American English. The researchers also identified neural populations associated with specific classes of phonetic phenomena, including separate clusters for consonants and vowels of different types, but their analysis suggested that these phonetic groupings were more of a byproduct of more natural groupings based on different types of muscle movement.

"Regarding coarticulation, the researchers discovered that our brains' speech centers coordinate different muscle movement patterns based on the context of what's being said, and the order in which different sounds occur. For example, the jaw opens more to say the word "tap" than to say the word "has" -- despite having the same vowel sound (/ae/), the mouth has to get ready to close to make the /z/ sound in "has." The researchers found that neurons in the ventral sensorimotor cortex were highly attuned to this and other co-articulatory features of English, suggesting that the brain cells are tuned to produce fluid, context-dependent speech as opposed to reading out discrete speech segments in serial order.

"'During speech production, there is clearly another layer of neural processing that happens, which enables the speaker to merge phonemes together into something the listener can understand," said Anumanchipalli.

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"'This study highlights why we need to take into account vocal tract movements and not just linguistic features like phonemes when studying speech production," Chartier said. He thinks that this work paves the way not only for additional studies that tackle the sensorimotor aspect of speech production, but could also pay practical dividends.

"'We know now that the sensorimotor cortex encodes vocal tract movements, so we can use that knowledge to decode cortical activity and translate that via a speech prosthetic," said Chartier."

Comment: All the hoopla about possible ape or monkey speech pals beside these findings. Like our consciousness our speech mechanism is amazingly complex and was developed from an enlarged brain ready to learn about 50+ thousand years ago , after our arrival 315,000 years ago. Earlier in our evolution our palate started to arch and our larynx began dropping, both to the advanced positions they have today. Why did that happen unless the future was planned for by a designer?