Investigators in the Cognitive Neuroscience Research Group (GRNC) at the Universitat de Barcelona, and located in the Parc Científic de Barcelona (PCB, Barcelona Science Park), have published an article reporting that rats distinguish between speech (prosodic) cues, specifically between sentences expressed in Dutch and in Japanese. The article has been published in this month's issue of the Journal of Experimental Psychology: Animal Behavior Processes

Directed by the researcher Juan Toro, this experiment demonstrates that rats can pick up cues from the rhythm and intonation of human speech. This finding may be useful in the study of language development in humans. The ability of the rats to distinguish one type of speech from another, which is studied through a test that uses two very different spoken languages, has now been documented in humans (adults and newborn) and in Tamarin monkeys. These primates are studied because in these experiments they show similar responses to human newborns. This study demonstrates the capacity of rats, the first non-primate mammal studied in this field, to distinguish prosodic cues, thereby demonstrating that mammals share this ability.

According to the authors of the study, “rats have not developed this ability to track prosodic cues for linguistic purposes, as is the case of human newborns, who coordinate the speech information they pick up in order to eventually make sense of language. Rats show this behaviour as a by-product of other abilities that have evolutionary relevance for them.”

The researchers at the GRNC trained rats to press a lever when hearing a synthesised 5-second sentence in Dutch or Japanese. The animals rewarded for responding to Japanese did not respond to Dutch and vice versa.

However, in Juan Toro’s words, “the linguistic sophistication of rats is limited”. For example, when the researchers used distinct human voices to express sentences, the rats had difficulty in distinguishing the two languages. Moreover, when the sentences were said backwards, a test of great interest in speech studies since it alters the speech patterns, neither could the rats distinguish between the two. In comparison, humans overcome the difficulty of distinct voices from infancy by learning a lexicon and syntax, phonology, word segments and semantic information. However, when sentences are read backwards to newborns the result of this test is also negative. The GRNC is a research group that focuses on the study of processes involved in the perception and production of language, with particular attention to the bilingual population. Within this line of research, Juan Toro studies the mechanisms involved in language perception in general and how it is related with other cognitive abilities and their relation to the structures present in non-humans animals.