Tuesday, May 8, 2018

Critical Periods in Speech Perception: New Directions

Werker, J. F., & Hensch, T. K. (2015). Critical periods in speech perception: new directions. Annual review of psychology66.

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

No comments:

Post a Comment