International Journal of Comparative Psychology

When humans perceive speech they process the acoustic properties of the sounds. The acoustics of a specific word can be different depending on who produces it and how they produce it. For example, a whispered word has different acoustic properties than a word spoken in a more natural manner; basically, the acoustics are “noisier.” A word will also sound differently depending on who speaks it, due to the different physical and physiological characteristics of the talker. In this instance, humans routinely normalize speech to retrieve the lexical meaning by solving what is termed the “lack of invariance” problem. We investigated these speech perception phenomena in a language-trained chimpanzee ( Pan troglodytes ) named Panzee to ascertain if more generalized auditory capabilities, as opposed to specialized human cognitive processes, were adequate to accomplish these perceptual tasks. In Experiment 1 we compared the chimpanzee’s performance when identifying words she was familiar with in natural versus whispered form. In Experiment 2 we investigated Panzee’s ability to solve the “lack of invariance” problem when familiar words were spoken by a variety of talkers (familiar and unfamiliar male and female adults, and children). The results of Experiment 1 demonstrated that there was no difference in her recognition for the two word types. The results of Experiment 2 revealed no significant difference in Panzee’s performance across all talker types. Her overall performance suggests that more generalized capabilities are sufficient for solving for uncertainty when processing the acoustics of speech, and instead favor a strong role of early experience.