NASA

· 08 Jun 2022

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How is speech formed in children?

Inner speech is an enigmatic everyday phenomenon that has been suggested to play an important role in psychological processes as diverse as memory, cognition, emotional regulation, auditory verbal hallucinations, and even consciousness and self-reflection.

The origins of modern interest in inner speech can be traced to the Russian developmental psychologist Vygotsky, who proposed that inner speech develops through the gradual internalization of linguistic interactions that have been shaped by social interaction.

Research has confirmed Vygotsky's view that private speech peaks in the preschool and early school years and gradually reduces in frequency in middle childhood. Children begin to understand the concept of inner speech in the preschool and middle school years.

Recent studies have shown that the neural correlates of self-directed speech are different for inner speech and overt speech. This suggests that there may be distinct neural mechanisms supporting inner speech and overt speech.

In the last 40 years, hundreds of functional imaging studies have examined the neural correlates of inner speech. These studies point to the involvement of the left inferior frontal gyrus, left angular and supramarginal gyri in the production and processing of inner speech.

Studies of task-dependent inner speech have shown that the IFG, temporo-parietal junction, and superior temporal regions are activated during spontaneous inner speech. However, a study of a single participant experiencing spontaneous inner speech showed that the IFG was not activated during spontaneous inner speech.

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The dorsal language pathway is divided into three segments: the fronto-temporal, fronto-parietal, and temporo-parietal segments.

According to different studies, the fronto-temporal and fronto-parietal tracts are the most likely to support inner speech, but the exact end points are not agreed upon.

The human language system is supported by a ventral language stream that runs medially to the temporal lobe. It includes the inferior fronto-occipital fascicle and the inferior longitudinal fascicle.

A tractography reconstruction of the left hemispheric language pathways shows that the pathway I fibers terminate in the premotor cortex.

Two influential models of language development and processing assign specific functions to the dorsal language stream, but developmental studies suggest that the dorsal language stream is under-developed in early childhood and is only used for higher language functions in adults.

Studies of word learning and repetition emphasize a specific functional directionality of the dorsal language pathway, in which processing of input phonological data in posterior regions precedes retrieval of articulatory information in frontal regions. However, direct cortical stimulation of anterior regions also results in evoked potentials in posterior regions.

Adult patient studies show that information propagates along both anterior and posterior directions in the human dorsal language pathway, and that some reciprocal fibers might be essential for inner speech development.

Some studies suggest that individuals with autistic spectrum disorder (ASD) use less inner speech than typically developing children, but further studies are needed to determine whether inner speech is affected by white matter abnormalities and whether behavioral performance correlates with dorsal stream anatomical integrity.

Three different lines of research suggest that the development of the dorsal language stream and inner speech occur at the same time in children, and that there is a link between these neuro-anatomical and psychological developments.

The development of language is not solely influenced by maturation of brain structures. Environment can induce brain changes, including changes in diffusivity parameters and FA, and these changes can be specific to the group that underwent the remediation program.

Using neurocomputational modeling, Schomers et al. (2017) demonstrated that the human anatomy of the dorsal pathway gives rise to stronger and longer-lasting neural activations, as well as parallel, rather than serial, activation. This suggests that human language evolved through changes in the AF.

Genetic studies have linked the FOXP2 gene to speech and language in humans. A specific variant of the FOXP2 gene is associated with inner speech in healthy individuals, putting inner speech as a main component in the evolution of language as a whole.



TimeLine:

From gurgles to giggles
Infant vocalisations are automatic to begin with. Then more intentional vocal communication develops.
Birth – 2 months
Reflexive sounds (e.g. crying, coughs)
2 – 4 months
Cooing and laughter
4 – 6 months
Vocal play, including with pitch, loudness, and funny sounds
6 months onwards
Babbling sounds
10 months onwards
Babble that sounds like speech (jargon & conversational babble)
Early language users (12 - 36 months)
have growing understanding and use of speech sounds
learn to say longer words with more sounds and more syllables
may have some typical "speech errors", such as gliding (rabbit—>’wabbit’).
Language and emergent literacy learners (30 - 60 months)
speech sounds and words are pronounced clearly while some typical speech errors still occur
have a growing awareness of how sounds work (phonology)
Language and emergent literacy learners may have very clear speech or may have some typical speech “errors”.