London: If you believe speech perception is a unique human trait, think again -- chimpanzees may also have the ability to understand language, says a new study.
The new research with a 25-year-old chimp named "Panzee" showed that the "well educated" animal can understand over 130 English words and can even recognise words in sine-wave form, a type of synthetic speech that reduces language to three whistle-like tones.
This shows that she isn't just responding to a particular person's voice or emotions, but instead she is processing and perceiving speech as humans do.
"The results suggest that the common ancestor of chimpanzees and humans may have had the capability to perceive speech-like sounds before the evolution of speech, and that early humans were taking advantage of this latent ability when speech did eventually emerge," lead researcher Lisa Heimbauer, at Georgia State University's Language Research Centre, said.
For their study, Heimbauer and colleagues tested Panzee on her ability to understand words communicated via sine-wave speech, which replicates the estimated frequency and amplitude patterns of natural utterances.
"Tickle," "M&M," "lemonade," and "sparkler" were just a few of the test words.
Even when the words were stripped of the acoustic constituents of natural speech, Panzee knew what they meant, correctly matching them to corresponding photos.
The findings, presented at the annual meeting of the Acoustical Society of America in San Diego, refute what is known as the "Speech is Special" theory.
"This argument proposes that besides humans being the only species able to produce speech, due to their anatomy, they also have a specialised cognitive module to process
speech," Heimbauer explained.
Supporters of the "Speech is Special" view have pointed to the fact that humans can understand speech, even when it is incomplete or highly distorted.
The alternative view to the hypothesis, she said, is that auditory processing is fundamentally similar across most mammals, and that many animals have latent abilities for
speech perception.
"What we are saying is that humans do not need unique cognitive abilities to process speech, and that instead, the general auditory processes that we share with apes, and probably a common ancestor, can be used to accomplish speech perception tasks," she said.
"Panzee then is able to understand speech because of her early experience in a speech-rich environment, and because she was taught about the association between words and their
meaning from a very early age."
"These are the same things that allow humans to learn how to understand speech," she said.
There is evidence that non-human primates use specific vocalisations in certain situations, but researchers hesitate in labelling these as being part of a "language."
Nonetheless, the findings suggested that, with education and experience, chimps can become proficient in aspects of human languages, allowing them to communicate certain feelings and desires with us, the researchers said.