Rats can tell the difference between Dutch and Japanese, suggests a new study. But it is not because some spy agency has bioengineered them to eavesdrop on conversations in Tokyo or Amsterdam.

They are simply recognising the difference in rhythmic properties of the languages, says Juan Toro, a neuroscientist at the University of Barcelona in Spain, whose study is part of an effort to trace the origins of the skills that humans use to analyse speech.

Human infants are extremely sensitive to the rhythmic regularities of language, which researchers think may help infants to break sound into patterns they can decipher as words. Earlier experiments showed that both tamarin monkeys and human infants can discriminate between Dutch and Japanese – two languages with rhythmic content that differs greatly.

Toro’s team trained rats to recognise either Dutch or Japanese – by pressing a lever in response to a short sentence – and then exposed them to sentences they had not heard before, in both languages.

They found that the rats responded significantly more often to the language they had been trained in – as long as the sentences were computer-synthesised or both languages were spoken by the same person. However, the rats could not tell the difference if the sentences were played backwards or were spoken by different people.

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