To us, all rat squeaks may sound alike, but the same may not hold true for the rodents. A new study reveals that rats are able to tell the difference between spoken Dutch and Japanese—a skill previously thought to be shared by only humans and tamarin monkeys.
One way to help figure out how language evolved in humans is to study the language-related abilities of other animals. Tamarin monkeys pick up patterns in language from rhythmic cues such as stress and intonation, just as human infants do, but scientists have wondered if other animals can use similar cues to discriminate between different languages.
To test this, a research team led by neuroscientist Juan Toro from the University of Barcelona trained a group of rats to press a lever after they heard synthesized sentences of Japanese or Dutch--languages spoken with very different intonation, stress, and phrasing. Once trained, animals familiar with one language stopped pressing the lever when they heard the other language. They resumed pressing the lever once their "own" language started playing again.
The rats were hearing cues specific to language, the researchers say. In another experiment, where the researchers trained a new group of rats with Japanese and Dutch sentences played backwards and then tested their discrimination ability, the rats were not able to distinguish between the two languages, the team reports in this month's issue of the Journal of Experimental Psychology. "Rats are able to find the differences between Dutch and Japanese sentences, but whatever information they are using is lost in backwards speech," Toro says. The missing cues are probably stress and intonation. Apparently, the ability to recognize these patterns evolved long before language did.
Aaron Blaisdell, a psychologist at the University of California, Los Angeles, notes that "the backward sentences were the really strong part of the test." He says that any animal with the ability to time and perceive tone should be able to discriminate languages with distinct rhythms.