Speech perception in a language-trained chimpanzee (Pan troglodytes).
Lisa A. Heimbauer, Michael J. Beran, Michael J. Owren · The Journal of the Acoustical Society of America · 2008
After decades of research, the question of whether humans perceive spoken language using a specialized “speech mode” remains unresolved. Studies in nonhumans suggest that animals perceive phonemic contrasts much as humans do, but involve subjects trained for thousands of trials on single discriminations. This work reports initial speech perception results from Panzee, a chimpanzee (Pan troglodytes) reared by humans speaking to her as they would to a child and also training her to use graphical wordlike “lexigrams.” Panzee comprehends approximately 126 spoken words, documented through a procedure in which a digitally presented spoken word is matched to one of four lexigrams presented on a monitor. First experiments have compared performance with natural digitized versions of 24 spoken words to synthetic LPC-based replicas and to whispered versions. Using a different subset of eight test words within each of three 96-trial sessions showed comparable mean performance for natural (83.3%), synthesized (82.5%), and whispered (78.5%) versions. Percent-correct performance on 24 trials representing the first time a given test word was heard was also comparable for synthesized (79.2%) and whispered (78.5%) sounds. The possibility that Panzee is showing speech-mode perception will be tested in experiments with noise-vocoded and sine-wave speech. [Work supported by NICHD.]