The Critical Period Hypothesis (CPH) suggests that there is a specific time frame during which an individual can acquire a new language with native-like proficiency. This critical period typically begins at the age of two and ends before puberty¹. According to this theory, learning a new language after this crucial window is more challenging and less successful.
In the field of developmental psychology, the critical period refers to a stage of development during which an individual's nervous system is highly receptive to environmental stimuli. If an individual does not receive appropriate experiences during this time, their ability to acquire new skills may weaken, ultimately affecting various social functions in their adult life. For language acquisition specifically, not learning a language during the critical period makes it highly unlikely for an individual to develop native fluency in their first language².
The critical period is closely tied to the concept of neuroplasticity, where an individual's brain is highly adaptable to learning new skills. During this time, the brain's connections, known as synapses, are receptive to forming new pathways in response to new experiences. As an individual ages, the brain becomes less plastic and less capable of forming new connections.
Similar to the critical period, researchers also use the terms "sensitive period" or "weak critical period" to describe a time when the brain is highly plastic and quickly forms new synapses. However, the sensitive period is believed to extend beyond puberty, although the exact timeframe is not strictly defined.
The Critical Period Hypothesis regarding language acquisition was first introduced by Eric Lenneberg in his book Biological Foundations of Language (1967). He proposed that achieving high-level proficiency in a language can only occur during this critical period and becomes increasingly difficult later in life. Lenneberg's theory was based on evidence from individuals who had certain childhood experiences that affected their first language acquisition. These cases included deaf children who did not develop native proficiency in verbal language after puberty, children who experienced brain injuries with better recovery prospects compared to adults, and children who were victims of child abuse during early childhood and had difficulty acquiring language due to a lack of exposure during the critical period.
One notable case that supports Lenneberg's theory is that of Genie, a victim of domestic abuse and social isolation. From the age of 20 months until 13 years old, Genie had no language exposure. When authorities discovered her, she was unable to speak. With direct teaching, she gradually acquired some language skills, but still struggled with basic grammar and conversation. Scientists working with Genie concluded that her inability to learn language during the critical period would greatly impact her ability to attain full competency in language throughout her life. Though she did show some improvement in her speech, it still exhibited abnormalities, and she struggled with social interaction.
While Genie's case largely supports Lenneberg's theory, there is still debate among academics and researchers. Some argue that her developmental delays were a result of inhuman and traumatic treatment, rather than her inability to learn a language during the critical period.
The Critical Period Hypothesis can also be applied to the acquisition of a second language. It pertains to adults or children who are fluent in their first language and attempt to learn a second one. Proponents of the CPH point to older learners' ability to grasp a second language compared to children and adolescents as evidence for its validity.
In general, younger learners tend to have a better grasp of a new language compared to older learners. This can be attributed to the role of the neuromuscular system in pronunciation.
While there may be exceptions where adults achieve fluency in a new language, they often retain a foreign accent that is not common among younger learners. This further supports the idea of a critical period for language acquisition and highlights the importance of early exposure to a language for achieving native proficiency.
It is widely believed that adults are less able to learn a second language fluently, as they have already passed the critical period for developing new neuromuscular functions. However, there have been rare cases of adults who have achieved near-native proficiency in a second language, making it difficult for researchers to determine a definitive correlation between age and language acquisition success.
While the concept of the Critical Period Hypothesis (CPH) has been widely accepted, there are some who argue that it may not apply to second language acquisition. They suggest that various factors, such as the amount of effort put in, the learning environment, and the duration of learning, may have a greater impact on a learner's success than their age.
The critical period refers to the optimal time for a person to learn a new language with native proficiency. It is believed that during this period, the brain is more malleable and can easily absorb and process new linguistic information.
The critical period is heavily influenced by the brain's increased neuroplasticity during this time. This makes it easier for a person to learn a new skill, such as a new language, as their brain is more adaptable to forming new connections and pathways.
The concept of the critical period was first proposed by Eric Lenneberg in his book 'Biological Foundations of Language' (1967). Through his research on language acquisition in children, he suggested that there is a specific period in a person's life where language learning is optimal.
Adults are past the critical period, so their brains are less neuroplastic than children, making it more challenging to learn a new language. This means that it may take more effort and practice for an adult to acquire a second language fluently compared to a child.
The critical period typically occurs from 2 years old until puberty, though some academic sources may have slightly different age ranges for this period. It is important to note that this period is not an exact science and may vary from person to person.
