Panzee doesn’t talk, but she knows a word when she hears one — even if it’s emitted by a computer with a synthetic speech impediment.
That’s not too shabby for a chimpanzee. Raised to recognize 128 spoken words by pointing to corresponding symbols, Panzee perceives acoustically distorted words about as well as people do, say psychology graduate student Lisa Heimbauer of Georgia State University in Atlanta and her colleagues. Panzee thus challenges the argument that only people can recognize highly distorted words, thanks to brains tuned to speech sounds and steeped in chatter, the scientists contend in a paper published online June 30 in Current Biology.
“Auditory processing abilities that already existed in a common ancestor of chimpanzees and humans may have been sufficient to perceive speech,” Heimbauer says.
Panzee’s immersion in talk began in infancy and fueled her word-detection skills, much as occurs in people, Heimbauer suggests.
Originally, the researchers thought that Panzee would need training to grasp the word task, since she had never heard artificially distorted words. But after hearing only one such word, the chimp identified the next four synthetically distorted words before making a mistake. “What were supposed to be training sessions became test sessions,” Heimbauer says.
Panzee’s immediate recognition of distorted words “is quite impressive and novel,” remarks psychologist Lori Holt of Carnegie Mellon University in Pittsburgh. In experiments conducted over the past 30 years, birds, rodents and other nonhuman animals have been trained to identify acoustically altered words. In contrast, Panzee apparently generalized from past experience hearing caretakers talk to distinguish acoustically transformed words, Holt says.
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Heimbauer’s group presented Panzee with spoken and synthetic versions of 48 words, such as apricot, that the chimp had previously learned to associate with symbols. Some synthetic words sounded fuzzy and noisy, much like what hearing-impaired persons perceive with cochlear implants. Other mock words consisted of three whistlelike tones.
Panzee identified a word by pointing to one of four symbols on a computer screen.
The researchers played the same natural and synthetic words for 32 college students, who wrote down what they heard.
Across several sessions, Panzee recognized substantially more words than would be expected if she guessed — an average of about 80 percent of spoken words, 55 percent of fuzzy words and 40 percent of tone words.
Human participants recognized all spoken words and an average of about 70 percent of fuzzy words and 40 percent of tone words.
It’s not known whether any other animals have Panzee’s word-recognition chops. Irene Pepperberg of Brandeis University in Waltham, Mass., predicts that parrots could decipher highly distorted speech on their own. Wild parrots recognize species-specific and individual vocal calls in noisy forests, amid cacophonous flocks of comrades, comments Pepperberg, who studies thinking and communication in African gray parrots.
Alex, a parrot trained by Pepperberg to use a vocabulary of roughly 100 words, immediately knew familiar words spoken in regional dialects and in thick foreign accents.
Researchers played words with different levels of distortion to Panzee the chimpanzee to test her word-recognition abilities. Hear the word “honeysuckle” as Panzee heard it in a natural voice
with fuzzy distortion (click here)
and as a series of synthetic tones (click here).
Credit: L. Heimbauer