Infants Recognize Voices, Emotions By 7 Months

A new study suggests that our brains develop specialized circuits to process human voices long before we learn to speak.

The study, which appears in the journal Neuron, looked at brain activity in 32 infants as they listened to recorded sounds. Half the children were 4 months old and the other half were 7 months old.

Some of the sounds they heard were nonhuman sounds, like chickens clucking, a bell ringing or a cuckoo clock. The rest were clearly human utterances including some words, though not in any language the children would have heard before.

While the children listened, researchers from Germany and the U.K. measured activity in certain areas within a part of the brain called the superior temporal cortex, which is just above the ear. Other studies have shown that these areas are where voices are processed in adults.

In 4-month-old infants, these areas did not differentiate between human voices and nonhuman sounds, says Tobias Grossman from the Centre for Brain and Cognitive Development at the University of London and the Max Planck Institute for Human Cognitive and Brain Sciences.

But it was a different story in the 7-month-old infants, Grossman says. The brain responses showed that "they process human voice distinctly from other kinds of sounds," he says.

The researchers wanted to know whether the older children's brains would also respond to the emotional meaning that's often conveyed through vocal intonation.

So they played unfamiliar words spoken with happy, unhappy and neutral intonations, and once again, certain areas of the brain seemed to know the difference.

The findings provide strong evidence that specialized voice processing in the brain develops sometime between the fourth and seventh month of life, Grossman says.

Problems with the brain systems that recognize and process human voices could offer an early warning of language difficulties.

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