This comprehensive
review paper discusses the steps that support language development within the
context of critical or sensitive periods. Critical or sensitive periods are
windows, typically early in development, during which a sensory system is open
to restructuring or learning based on input from the environment.
Original views on a critical period
for language acquisition proposed that this window closed at the onset of
puberty (e.g.: Lennenberg, 1967). However, this view has become much more
nuanced, with language acquisition being characterized by multiple critical and
sensitive periods throughout early development. The research reviewed in this
paper demonstrates that infants become attuned to the properties of language gradually
throughout development. This process of development starts with a sensitivity
to global properties of language, such as being able to distinguish speech
versus non-speech sounds. As infants develop, they become more sensitive to the
fine-grained details in their native language. These processes are defined by
critical periods, and development within these critical periods relies on both
biological and environmental factors.
Some of the strongest evidence for
critical periods in language acquisition comes from work examining phoneme
discrimination in young infants. Phonemes are the units of sound in a language,
such as the sounds /k/, /æ/, and /t/ in the word “cat”. Young infants are
capable of discriminating phonemes from across the world’s languages. However,
there is a process of perceptual
narrowing around 8 to 10 months of age, which sharpens their perception to
only those phoneme distinctions that are used in their native language. For
example, an infant reared in an Japanese-speaking environment could
discriminate between the phonemes /r/ and /l/ at 6 but not 10 months of age.
This is because the phonetic distinction between these phonemes is not present
in the Japanese language. However, an infant reared in an English-speaking
environment can continue to discriminate between these phonemes after 10 months
of age because the phonetic distinction between /r/ and /l/ is present in the
English language. Once phoneme categories are in place at around 10 months of
age, infants begin to show sensitivity to more complex aspects of language,
such as recognizing familiar words in their native language. This example
highlights how native language experience shapes perception, and the gradual and
sequential native of language development.
Critical periods can be impacted by both
biological and environmental factors. For instance, exposure to pharmacological
agents during pregnancy can affect language critical periods. Additionally,
factors such as being raised in a bilingual environment or receiving a cochlear
implant can alter critical periods. Critical periods are important to
understand because they demonstrate how early language exposure shapes later
language skills. Overall, by examining language critical periods, clinicians
and researchers can broaden their understanding of how language development
unfolds.
Blogger: Nicolette Noonan is a PhD Candidate in Psychology, supervised by Dr. Lisa Archibald and Dr. Marc Joanisse
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