Final answer:
Infants are born with the ability to differentiate between all human phonemes, known as universal phoneme sensitivity, which narrows to the phonemes of their environment by their first birthday. This early specialization aids language acquisition. Adults learning a second language, however, do not have the same level of phoneme sensitivity and often require more effort and instruction.
Step-by-step explanation:
Universal Phoneme Sensitivity in Infants and Adults
Infants are born with the remarkable ability to differentiate between all human phonemes, which are the distinct units of sound that distinguish one word from another in language. This ability, known as universal phoneme sensitivity, enables babies to perceive sounds from all languages, regardless of the language environment they are exposed to. According to Jensen (2011), infants can initially discriminate among the phonemes of any language, but this ability becomes specialized to the phonemes of their environment by around one year of age. Similarly, research by Werker and Tees (1984) and Werker and Lalonde (1988) supports that the sensitivity to non-native language sounds decreases as infants tune into their native language. This specialization is essential for language acquisition as it helps infants focus on the sounds relevant to their language, but it also means that the ability to effortlessly learn any language's phonemes declines.
For adults learning a second language, this phoneme sensitivity is not as sharp as it is during infancy. Language learning in adulthood often requires explicit instruction and practice to recognize and produce non-native phonemes correctly. Research has shown that the foundations laid in early infancy play a significant role in future language development and proficiency in both first and second languages (Jensen, 2011).
Beyond phoneme sensitivity, infants are also sensitive to prosody—the rhythm, stress, and intonation of speech—which is evidenced by their preference for speech and synchronization between visual and audio cues (Blossom & Morgan, 2006). Moreover, infants have been found to prefer their mother's voice over a stranger's, reinforcing the significance of the early acoustic environment on language and communication development (Mills & Melhuish, 1974).