Developmental linguistics is the study of the development of linguistic ability in an individual, particularly the acquisition of language in childhood. It involves research into the different stages in language acquisition, language retention, and language loss in both first and second languages, in addition to the area of bilingualism. Before infants can speak, the neural circuits in their brains are constantly being influenced by exposure to language.
The neurobiology of language contains a "critical period" in which children are most sensitive to language. The different aspects of language have varying "critical periods". Studies show that the critical period for phonetics is toward the end of the first year. At 18 months, a toddler's vocabulary vastly expands. The critical period for syntactic learning is 18-36 months. Infants of different mother languages can be differentiated at the age of 10 months. At 20 weeks they begin vocal imitation.
Beginning when babies are about 12 months, they take on computational learning and social learning. Social interactions for infants and toddlers is important because it helps associate "perception and action". In-person social interaction rather than audio or video better facilitates learning in babies because they learn from how other people respond to them, especially their mothers.
Babies have to learn to mimic certain syllables, which takes practice in manipulating tongue and lip movement. Sensory-motor learning in speech is linked to exposure to speech, which is very sensitive to language. Infants exposed to Spanish exhibit a different vocalization than infants exposed to English. One study took infants that were learning English and made them listen to Spanish in 12 sessions. The result showed consequent alterations in their vocalization, which demonstrated Spanish prosody. One study used MEG to record activation in the brains of newborns, 6 months olds and 12 months olds while presenting them with syllables, harmonics and non-speech sounds. For the 6 month and 12 month old, the auditory and motor areas responded to speech. The newborn showed auditory activation but not motor activation. Another study presented 3 month olds with sentences and recorded their brain activity via fMRI motor speech areas did activate. These studies suggest that the link between perception and action begins to develop at 3 months.
When babies are young, they are actually the most sensitive to distinguishing all phonetic units. During an infant’s 1st year of life, they have to differentiate between about 40 phonetic units. When they are older they have usually been exposed to their native language so much that they lose this ability and can only distinguish phonetic units in their native language. Even at 12 months babies exhibit a deficit in differentiated non-native sounds. However, their ability to distinguish sounds in their native language continues to improve and become more fine-tuned. For example, Japanese learning infants learn that there is no differentiation between /r/ and /l/. However, in English, "rake" and "lake" are two different words. Japanese babies eventually lose their ability to distinguish between /r/ and /l/. Similarly, a Spanish learning infant cannot form words until they learn the difference between works like "bano" and "pano", because the /p/ sound is different than the /b/ sound. English learning babies do not learn to differentiate between the two.
Babies learn early on to recognize prosodic cues. English speaking babies learn that the English language places a lot of stress on the first syllable, which is called trochaic or strong-weak prosody. The Polish prosodic pattern is the opposite and is called weak-strong or iambic prosody. At 7.5 months, English speaking infants can recognize their native pattern and segment words accordingly. They are able to identify the stress on words like "pencil" or "stapler". However, when they hear a phrase like "guitar is", they will perceive "tar is" as a unit since that is where the stress occurs.
Exposing babies to music can improve their listening skills. Music tunes their attention skills and helps them distinguish different sounds. A study was done that compared activity in the prefrontal cortex in a group of babies who had 12 sessions of music class compared to babies who took 12 sessions of a social class with no music. The study found that babies in the music classes had greater activity in the prefrontal cortex.
- Kuhl, Patricia K. (1 September 2011). "Early Language Learning and Literacy: Neuroscience Implications for Education". Mind, Brain and Education : The Official Journal of the International Mind, Brain, and Education Society. 5 (3): 128–142. doi:10.1111/j.1751-228X.2011.01121.x. PMC 3164118. PMID 21892359.
- "Babies Learn Language Socially - Cognitive Neuroscience Society". 29 March 2015.
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