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ATLANTA - A team of researchers from Georgia State University working with a language-enriched chimpanzee have found that she can perceive words from both natural speech and distorted speech. This gives scientists more insight into questions surrounding human speech perception.
The researchers, led by Lisa Heimbauer, a doctoral student with associate professor Michael Owren, involved computerized tests given to Panzee, a chimpanzee at the university's Language Research Center (LRC). Panzee was raised from eight days old by humans, and she was spoken to and interacted with as human infants are, enriching her ability to understand human language.
Panzee can recognize about 130 spoken words that she reliably identifies by pointing to symbols, called lexigrams, which were developed in the 1970s by Duane Rumbaugh and his colleagues. In the experiments, Panzee and humans were tested with 48 different words, both in naturally spoken and computer-generated, synthetic forms.
Two types of synthetic speech were used, including noise-vocoded speech, which simulates the input hearing-impaired persons with cochlear implants experience, and sine-wave speech, consisting of three whistle-like tones.
Both synthetic forms are missing many of the cues that are normally present in speech, and some scientists believe that only humans can understand them only because of specialized language capabilities.
The researchers found that even without training, Panzee immediately was able to reliably identify words in these synthetic forms.
Panzee's ability to spontaneously recognize the synthetic words shows that experience, rather than specialization, is the critical factor in human speech-perception capabilities.
"It suggests to us that even though she never heard these synthetic forms, she is bringing similar kinds of perceptual mechanisms to bear that humans have, even though her knowledge of words and speech sounds is very limited by human standards," Owren said.
The research may help scientists better understand the development of speech perception abilities in human children, as well as providing information about when and how speech perception abilities evolved in humans.
The team plans to test Panzee in further speech perception tasks to gather more evidence about how she compares to humans. Finding similarities between the two species provides clues as to what the capabilities of their common evolutionary ancestor may have been.
"Next we would like to investigate in more detail what cues Panzee may be using in perception of both natural and synthetic speech, in comparison to what humans do," Heimbauer said.
The research team included Heimbauer, Michael J. Beran, a senior research scientist, and Owren. The article, "A Chimpanzee Recognizes Synthetic Speech with Significantly Reduced Acoustic Cues to Phonetic Content," is available in the journal Current Biology 21, 1-5, doi:10.1016/j.cub.2011.06.007.
July 7, 2011