Rats can distinguish languages,
New York Times
Jan. 10, 2005
If you talk to a rat, you will not get an answer. But a team of Spanish
neuroscientists has shown that a well-trained rat may be able to determine what
language you are speaking.
Every language has distinctive
rhythms and intonations, and awareness of them is an important step in acquiring
language. Only humans can learn to speak, but it has been demonstrated that
tamarin monkeys, like newborn human infants, can distinguish the unique rhythms
of a language even though meaning escapes them.
In other words, they know when someone is speaking their language, even though
they have no idea what is being said. Researchers have theorized that this
ability extends to other mammals as well, but until now no nonprimate has ever
demonstrated the capacity.
In the new study, led by Juan Toro, a doctoral candidate at the University of
Barcelona, researchers found that rats trained in either Dutch or Japanese
appeared able to distinguish the two languages.
The rats were trained by having them listen to synthesized sentences in the
languages. Dutch and Japanese were chosen because of their vastly different
rhythms. The sentences had no semantic content, but were intended to reproduce
the rhythms of the language without using any real words - approximately what a
comedian might do with foreign languages for humorous effect.
This simplified form of language, when spoken in a synthesized voice, leaves
only rhythm as a cue, eliminating complicating factors like semantic content or
the quality of the voice of a particular speaker.
For the Dutch group, the rats were rewarded with food only when they pressed a
lever after hearing Dutch sentences. The Japanese group was rewarded only for
lever pressing after hearing Japanese sentences. Eventually, both groups learned
to press the lever only when hearing a sentence in their own languages.
Next, the rats listened to four synthesized sentences in the language they had
not learned. When the Dutch mice were presented with Japanese sentences, they
showed no recognition; when the Japanese mice were presented with Dutch, they
were similarly baffled. But when presented with a sentence in their own
languages, even a sentence they had never heard before, the rats recognized the
characteristic rhythm and pressed the lever correctly.
The researchers said the rats appeared to have generalized some of the rules of
their language and, at least in this limited way, were able to understand an
entirely new sentence, a distinctive mark of language acquisition. When the
researchers played the same sentences with the tape running backward, the rats
were unable to understand what language was being spoken - exactly what happens
with tamarins and human infants.
Rats, of course, have limitations. They had considerably more difficulty in
telling one language from another when listening to normal speech, especially
when uttered by different speakers, the researchers found. The multiplicity of
cues in ordinary conversation - intonation, the speaker's sex, pitch and so on -
utterly confused them.
Human infants have some difficulty with different voices, too, but they quickly
overcome it, learning to recognize their own language no matter who is talking
and however varied the pitch and intonation.
"What these results suggest," Toro said in an e-mail interview, "is that we
share with other animals the ability to perceive some regularities, such as
rhythm, in the speech signal. This is interesting because several studies with
human infants have shown that these regularities may open the door to language
Does this mean rats and monkeys have the potential to understand human speech?
No, said Toro. But he added, "Even though human language is special and does not
seem to have parallels in the communicative systems of other species, some basic
abilities we use for acquiring it may be present in other animals."