Human evolution; our complex speech mechanism, 1 (Introduction)

by David Turell @, Tuesday, July 03, 2018, 23:41 (161 days ago) @ David Turell

Until it is understood how complex is our ability to speak, how the changes from the ape form are so different and require obviously a tremendous number of mutations, it becomes obvious we are highly different from apes, and much more than primates. We are a giant highly different step beyond. Please read the article for completeness provided by the diagrams and for the voluminous text which has new research beyond the book I've quoted from 1992:

https://www.the-scientist.com/features/why-human-speech-is-special--64351?utm_campaign=...

"as most speech scientists agree, there is no such thing as pure phonemes (though some linguists still cling to the idea). Discrete phonemes do not exist as such in the speech signal, and instead are always blended together in words. Even “stop consonants,” such as , [p], [t], and [g], don’t exist as isolated entities; it is impossible to utter a stop consonant without also producing a vowel before or after it. As such, the consonant [t] in the spoken word tea, for example, sounds quite different from that in the word to. To produce the vowel sound in to, the speakers’ lips are protruded and narrowed, while they are retracted and open for the vowel sound in tea, yielding different acoustic representations of the initial consonant.

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"computer systems that recognize and synthesize human speech are commonplace. All of these programs, such as the digital assistant Siri on iPhones, work at the word level. What linguists now know about how the brain functions to recover words from streams of speech now supports this word-level approach to speech reproduction. How humans process speech has also been molded by the physiology of speech production. Research on the neural bases of other aspects of motor control, such as learned hand-arm movements, suggests that phonemes reflect instruction sets for commands in the motor cortex that ultimately control the muscles that move our tongues, lips, jaws, and larynxes as we talk. But that remains a hypothesis. What is clear about language, however, is that humans are unique among extant species in the animal kingdom. From the anatomy of our vocal tracts to the complexity of our brains to the multifarious cultures that depend on the sharing of detailed information, humans have evolved the ability to communicate like no other species on Earth.

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" In the human body, the lungs serve as the bellows, providing the source of acoustic energy for speech production. The supra-laryngeal vocal tract (SVT), the airway above the larynx, acts as the pipes, determining the formant frequencies that are produced.

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"During speech, however, the diaphragm is immobilized and alveolar air pressure is maintained at an almost uniform level until the end of expiration, as a speaker adjusts her intercostal and abdominal muscles to “hold back” against the force generated by the elastic recoil of the lungs.

"This pressure, in combination with the tension of the muscles that make up the vocal cords of the larynx, determines the rate at which the vocal cords open and close—what’s known as the fundamental frequency of phonation (F0), perceived as the pitch of a speaker’s voice.

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Adult women produced formant frequencies that were higher for the same vowels because their SVTs were shorter than the men’s. Adolescents’ formant frequencies were higher still. Nonetheless, human listeners are typically able to identify these spoken vowel sounds thanks to a cognitive process known as perceptual normalization, by which we unconsciously estimate the length of a speaker’s SVT and correct for the corresponding shift in formant frequencies.

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"In short, people unconsciously take account of the fact that formant frequency patterns, which play a major role in specifying words, depend on the length of a speaker’s vocal tract. And both the fossil record and the ontogenetic development of children suggest that the anatomy of our heads, necks, and tongues have been molded by evolution to produce the sounds that clearly communicate the intended information.

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"In addition to the anatomy of the SVT, humans have evolved increased synaptic connectivity and malleability in certain neural circuits in the brain important for producing and understanding speech. Specifically, circuits linking cortical regions and the subcortical basal ganglia appear critical to support human language."

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