Theories of Language Development

Humans, especially children, have an amazing ability to learn language. Within the first year of life, children will have learned many of the necessary concepts to have functional language, although it will still take years for their capabilities to develop fully. Some people learn two or more languages fluently over their lives (often starting from childhood); these people are bilingual or multilingual. Multiple theories have been proposed to explain the development of language, and related brain structures,  in children.

Skinner: Operant Conditioning

B. F. Skinner believed that children learn language through operant conditioning; in other words, children receive "rewards" for using language in a functional manner. For example, a child learns to say the word "drink" when she is thirsty; she receives something to drink, which reinforces her use of the word for getting a drink, and thus she will continue to do so. This follows the four-term contingency that Skinner believed was the basis of language development—motivating operations, discriminative stimuli, response, and reinforcing stimuli. Skinner also suggested that children learn language through imitation of others, prompting, and shaping.

Chomsky: Language Acquisition Device

Noam Chomsky's work discusses the biological basis for language and claims that children have innate abilities to learn language. Chomsky terms this innate ability the "language acquisition device." He believes children instinctively learn language without any formal instruction. He also believes children have a natural need to use language, and that in the absence of formal language children will develop a system of communication to meet their needs. He has observed that all children make the same type of language errors, regardless of the language they are taught. Chomsky also believes in the existence of a "universal grammar," which posits that there are certain grammatical rules all human languages share. However, his research does not identify areas of the brain or a genetic basis that enables humans' innate ability for language.

Piaget: Assimilation and Accommodation

Jean Piaget's theory of language development suggests that children use both assimilation and accommodation to learn language. Assimilation is the process of changing one's environment to place information into an already-existing schema (or idea). Accommodation is the process of changing one's schema to adapt to the new environment. Piaget believed children need to first develop mentally before language acquisition can occur. According to him, children first create mental structures within the mind (schemas) and from these schemas, language development happens.

Vygotsky: Zone of Proximal Development

Lev Vygotsky's theory of language development focused on social learning and the zone of proximal development (ZPD). The ZPD is a level of development obtained when children engage in social interactions with others; it is the distance between a child's potential to learn and the actual learning that takes place. Vygotsky's theory also demonstrated that Piaget underestimated the importance of social interactions in the development of language.

Piaget's and Vygotsky's theories are often compared with each other, and both have been used successfully in the field of education.

Language and Cognition

The following timeline gives an overview of the ages at which children generally acquire language:

• 4–6 months: Babbling using all sounds.
• 6–9 months: Babbling becomes more focused—narrowing of sounds.
• 10–12 months: First words develop.
• 18–24 months: Children begin using two-word phrases (example: "Me up" or "Get milk").
• 2–3 years: Children begin using three-word phrases in correct order with inflection.
• 4–5 years: Children start speaking with nearly complete syntax.
• 5–7 years: Children begin using and understanding more complex language.
• 9 years and older: Children understand almost all forms of language.

In language acquisition, there is a hypothesis that a "critical period," or a time when it is optimal to learn a language, exists in children. Part of this hypothesis is that if a child is not exposed to a language in the early years of life, he or she will never have full intuitive command of a first language. 

One of the canonical case studies that supporters of the critical-period hypothesis turn to is Genie the "feral child," a young girl born in 1957 who, due to horrible abuse and neglect, never learned a language. She never managed to fully acquire verbal language as a result.