Having brains that weigh only about two grams apparently doesn't stop rats from discriminating between languages. A team of neuroscientists from the University of Barcelona in Spain has successfully trained rats to respond differently to randomly generated sentences in Japanese and Dutch.
This study, led by doctoral candidate Juan Toro, is the first to show language discrimination ability in a non-primate animal. Though there is no evidence that the rats understand meaning in these languages, they are, according to the theory of evolution, human's oldest ancestor that has demonstrated (in a controlled study) that they know when the language they've been trained with is spoken.
This language test focuses on distinctive rhythms, phoneme patterns and intonations in language - sentences played for the animals both during training and testing had no semantic content. Words were made up and strung together from typical syllable patterns in the language. Dutch and Japanese were chosen as test languages for their dramatically different rhythms.
Moreover, a computer generated voice had to be used for all sentences, since changes in pitch and tonal quality in different human voices confused the animals. Interestingly, human infants as well as students of a new foreign language are similarly confused by listening to different speakers in their earliest stages of language learning, but unlike rats, they rapidly pick up the differences in pitch and tone. The problem seems especially pronounced in switching from female to male Japanese speakers and vice versa - another reason for the use of the synthetic computer voice.
In the experiments, published in the journal "Animal Cognition," rats received a food reward for pressing a lever in response to their assigned language (only Dutch or only Japanese).
Next, these rats listened to multiple, different sentences in the language they had not previously heard. Japanese-trained and Dutch-trained rats alike were puzzled at the other language. Their reactions were similar to control animals that had heard random sentences played in reverse: No rats pushed their levers. In the midst of phrases in the other language, if a sentence is played in their original language, even if it's one they had never heard before, they did not hesitate to pounce on the food lever.
Although the results are interesting, they do not suggest that rodents with enough training have the potential to understand spoken languages. According to Toro, the results of this study simply define a "capacity to discriminate languages from different rhythmic classes [that] depends on general perceptual abilities that evolved at least as far back as the rodents."
Prior to this experiment, the most impressive study using this same language task was conducted with cotton-top Tamarin monkeys. The fact that these primates performed well on the Dutch-Japanese task was considered impressive, which revealed the perceptual abilities that these monkeys share with human infants.
This skill for deciphering rhythmic patterns in oral communication is essential to human acquisition of language. Though human linguistic abilities are unparalleled in any other species, it is fascinating how many abilities critical to language acquisition evolved long before even the earliest primate.
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