A newborn can tell apart roughly 600 consonants and 200 vowels, the full set used across the world’s languages. By their first birthday, many of those distinctions have faded, narrowed down to the sounds their own family speaks.
Every sound, for a few months only
The shrinking starts around six months old, in a process researchers call perceptual narrowing. Before that point, an infant can hear a contrast between two sounds even when neither exists in the language spoken around them. After it, many of those contrasts disappear from what the baby notices.
An English-learning baby, for instance, loses the ability to tell apart two versions of the letter “t”. A baby hearing Hindi or Urdu keeps that ability, because those languages use the distinction to change a word’s meaning. Vowel sounds narrow first, around six months, because they are longer and more stable in speech. Consonants follow later, around ten to twelve months, since they are shorter and change faster in fluent speech.
The loss is part of learning. It helps a baby discover and learn the words of their own language.
The cost shows up later, when an adult tries to learn a second language. Japanese speakers, for example, often struggle to hear the difference between English “l” and “r”, because Japanese never treats them as separate sounds.
What babbling sounds like as it happens
While perception is narrowing, production is catching up in its own way. Canonical babbling, the repetitive “bababa” or “dadada” syllables that most people picture when they think of a baby’s babble, typically starts between six and eight months old. Simpler vowel sounds like “ah” appear earlier still, around three to four months.
Gert Westermann, a professor of psychology at Lancaster University, says babies favour the easiest sounds to make. “Ga” and “guh” need only an opening and closing of the throat. “Sh” and “f” sounds require pressing the lips and teeth together and blowing hard, which takes longer to master.
Babbling already carries the accent of the language a baby is hearing. Andrew Jessop, a psychologist at the University of Liverpool, points to a video of 19-month-old Orla as a clear example. Her babbled protests at nap time carry a distinct Liverpool accent. English-learning babies tend to babble syllables that end in consonants, such as “ack” or “et”. French-learning babies stretch out their final vowel sound instead, drawing out an “oh” into “oooh”.
Understanding arrives before speaking does
A baby understands far more than they can say. By nine months old, infants show signs of recognising common words such as “milk” and “nose”, long before their motor skills let them say the words back. Between one and two years old, a child’s vocabulary of understood words grows quickly, while the words they can produce lag behind. Researchers call this gap the comprehension-production asymmetry.
The same tuning that shapes perception also shapes what sound sequences a baby expects to hear. Nine-month-olds already show a preference for sound combinations that occur in their own language, favouring a plausible English word like “find” over an impossible one like “fnid”.
From babble to word
Most children say their first real word around twelve months old, though the exact age varies from child to child. By then, the vowel sounds in a baby’s babbling have moved toward those of the language they have been hearing.
Perception narrowing to one language and babbling shifting toward that language’s sounds develop in parallel. Researchers at the University of York study the relationship between babble and early words. They name how and when a baby’s perception and production come together as one of their major interests.
What the research agrees on is the sequence: a baby arrives able to hear almost anything, and spends the first year of life trading that range for expertise in the sounds of one language.
