In English, changing the pitch of a word can change its emotion, but not its meaning. In a tone , however, pitch is of the word . Thai, example, has tones. The “mai” can mean “new”, “silk”, “wood” or “not”, on the rises, or stays level.

Newborn babies can hear the differences between the sounds of every human language. This , however, does not . By the of their first , infants specialists in the spoken them. They stop contrasts that their own language does not .

At birth, babies are what researchers call universal listeners. In experiments, infants from English-speaking homes can distinguish pairs of Hindi sounds that English-speaking adults find almost impossible to tell apart.

This remarkable ability changes during the first year. Studies by the psychologist Janet Werker and others have shown that between about six and twelve months of age, babies become better at hearing the sound contrasts of the language around them and worse at hearing contrasts that their language does not use. By their first birthday, many have lost much of their earlier sensitivity.

Researchers do not see this as a loss so much as a form of efficiency. A brain that focuses on the sounds that matter can process speech faster and learn words more easily.

Exposure appears to be crucial, and the quality of that exposure matters. In one well-known study, American infants who spent time with a Mandarin-speaking adult in person kept their ability to hear certain Mandarin sounds. Infants who heard the same language only through a video recording did not.

For many adult learners, the tones of Thai, Mandarin or Vietnamese are the hardest part of the language. English speakers do use pitch, but mainly to express attitude or to mark a question. When they hear a rising tone, their brains tend to treat it as emotion rather than as part of the word’s identity.

Research suggests that this habit can be changed with focused training. In laboratory studies, adults who practiced identifying tones for several hours, with immediate feedback on each answer, improved noticeably, and some of their gains lasted for months. Training that used many different voices was especially effective, perhaps because it taught learners to listen for the pattern rather than for one speaker’s voice.

Musical experience may help too. Several studies have found that musicians tend to perceive tones more accurately than non-musicians, although the advantage is modest.

The lesson for learners is encouraging. Hearing tones is not a talent that people either have or lack. It is a skill that responds to deliberate, well-designed practice.