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The mysterious process of speech production: Do you know how we turn thoughts into words?
Speech production is the process of converting thoughts into speech sounds, a process that includes the selection of words, the organization of relevant grammatical forms, and the subsequent use of the vocal tract through the motor system to produce sounds. Speech production can be spontaneous, such as the custom-made words produced by a person while having a conversation; reactive, such as naming a picture or reading written text; or imitative, such as repeating speech. In everyday fluent conversation, people can produce about four syllables, ten to twelve phonemes, and two to three words per second from their vocabulary, although the total vocabulary may be one hundred thousand to more than one hundred thousand. Surprisingly, the error rate in speech production is relatively low, with errors occurring at a frequency of approximately one in 900 words in spontaneous speech.
Behind speech is a complex psychological process that involves a deep understanding of thought and the organization of corresponding language.
In the process of speech generation, airflow through the lungs is usually required to provide pressure, and sound is produced through the vocalization of the glottis, which then forms different vowels and consonants through changes in the vocal tract. However, speech production does not always rely on the lungs and glottis; for example, in the case of alaryngeal speech, phonation can occur via the upper part of the vocal tract. Guttural sounds like Donald Duck are examples of this type of speech.
The production of speech can be associated with the production of gestures that enhance the intelligibility of spoken utterances. Speech development throughout a person's life begins with a baby's first babbling and becomes mature language by the age of five. The early speech stage usually begins around one year of age and is called the holophrastic phase. Between one and a half and two and a half years old, infants can produce short sentences, a period known as the telegraphic phase. After two and a half years old, the infant's language system gradually develops, and over time they can produce language like adults.
The process of speech production can be broken down into three main stages: conceptualization, formation, and articulation.
During the conceptualization stage, the speaker's intention links the desired concept to the specific speech sound to be uttered. Predictive intent information is formed here to specify the concept that needs to be expressed. Next comes the formative stage, during which the required language forms are created, including grammatical coding, morpho-phonological coding, and phonetic coding. Finally, the articulation stage is performed by the articulatory organs such as the lungs, glottis, larynx, tongue, lips, and jaw, which ultimately produce speech.
In neuroscience, right-handed speech production mainly relies on areas of the left cerebral hemisphere, including the bilateral supplementary motor areas, the left posterior inferior frontal gyrus, the left insular area, the left primary motor cortex, and the Temporal lobe. The cerebellum is also involved in the rapid, smooth, and rhythmic organization of speech syllables.
Disorders of speech production
The speech production process can be affected by a variety of disorders, which may manifest as various challenges in the speech process. In the process, researchers have discovered that the study of speech errors not only helps us understand the mechanisms of speech production, but also reveals the rule cognition reflected by speech errors. Even in our errors, speech is usually still grammatically correct.
Evolution of speech production models
With the in-depth study of speech production, scholars have proposed a variety of speech production models to try to explain this complex process. The core elements of these models include: concept identification, selection of grammatical framework, lexical retrieval, phonemic conversion, and preparation of pronunciation instructions.
From the history of speech production, early research focused on speech comprehension. It was not until the late 1960s that the study of speech errors promoted the establishment of speech production models.
For example, Fromkin's 1971 generative model of pronunciation, which consists of six stages, attempts to explain the results of speech error research. Subsequently, Garrett's model published in 1975 further improved the old model and reconstructed it based on speech error data. Both Fromkin's model and Garrett's model aim to better understand various aspects of speech production.
In addition, the lexical network model proposed by Dell in 1994 provides a basis for speech production, helping people understand the process of word selection and its organization in speech. Levelt's model further refined the concept of lexical network in 1999 and revealed how people use relevant grammatical and semantic information when choosing appropriate language.
The developmental process of speech production is also important. Babies begin to imitate facial expressions and try to coordinate sounds at seven months old, a process that lays the foundation for later language development. Through language stimulation and reading, infants and young children's vocabulary increases significantly. Studies have shown that children who lack language input can have a vocabulary of up to 32 million words less than children who are read to regularly.
So, have you ever thought about which factors in the speech production process have the greatest impact on our communication effectiveness?
