Regardless of the language they are primarily immersed in at home, newborn infants have a well-documented penchant for identifying the slightest differences in the sounds of the world’s languages.
By the time a baby reaches one year in age, however, their perceptual abilities are more finely tuned to their native language’s sounds. This process makes us really good at listening to our native language but it also makes it really difficult for monolingual individuals to process the different sounds of a foreign language — for example, native English speakers may struggle to hear the difference between the “r” and “rr” sounds in the Spanish words “pero” and “perro.”
While this phenomenon has been observed for several decades, researchers are still seeking out the underlying learning mechanism that more concretely explains why it occurs. A team of researchers at the University of Maryland and Ecole Normale Supérieure in Paris recently published a study that’s shedding light on that very mechanism.
“Understanding how this early learning proceeds is important as it serves as a foundation for later development,” reads the study. “However, it has proven difficult to identify a learning mechanism that works on the true input infants hear.”
In order to understand the sounds of their native language, children need to understand which sounds contrast with which sounds. For example, children learning North American English will grow to learn that the first consonants in “tore” and “door” represent different phonemes of the language and are contrastive.
Children begin narrowing in on the contrasts in their native language by around one year of age — before that, they can identify contrasts like this in pretty much any human language. In past studies, this has typically been observed by analyzing the way infants respond to very clean and carefully produced audio segments, rather than spontaneous speech, which can be noisy and sometimes unclear even to adults.
“This is one of the first phonetic learning accounts that has been shown to work on spontaneous data, suggesting that infants could be learning which acoustic dimensions are contrastive after all,” said Kasia Hitczenko, a psycholinguist and the lead author of the paper.
The recently published study attempts to do so with more natural speech tokens. In this study, the researchers observed infants listening to Dutch, Japanese, and French speech, paying close attention to the way they recognize vowel length. While Dutch and Japanese both have contrasts between long and short vowels, French does not.
The researchers proposed that the infants recognize the different contexts in which the vowels occur, allowing them to determine a general distribution of the environments in which the sounds are typically pronounced. This further enables them to draw conclusions about what sounds contrast with which in their native language.
