The Mind of an Ape is a 1983 book by David Premack and his wife Ann James Premack. The authors argue that it is possible to teach language to (non-human) great apes. They write: "We now know that someone who comprehends speech must know language, even if he or she cannot produce it." The authors David Premack, emeritus professor of psychology at the University of Pennsylvania, and Ann James Premack, a science writer, began teaching language to apes in 1964. Premack started his work at the Yerkes Laboratories of Primate Biology in Orange Park, Florida, a program at the University of Florida, continued it at the University of Missouri, then at the University of California, Santa Barbara and the University of Pennsylvania. The apes The subjects of the program, nine chimpanzees, were reared in a laboratory environment specifically designed to stimulate their intellect, as animals raised otherwise fail to thrive. This was in contrast to the traditional psychology lab where the animals are caged and remain in solitude. Sarah, born in 1959, demonstrated use of an invented language. Gussie failed to learn any words. Elizabeth and Peony were trained in the language. Walnut, a late arrival, also was trained in the language, but failed to learn any words. Jessie, Sadie, Bert, and Luvie, 1975 controls, were not trained in the language, but demonstrated pointing. Language suitable for an ape The language designed by Premack for an ape was not verbal; Premack's chimpanzee program differed from that of a separate research program in which other chimpanzees were raised in a human family in parallel with human babies, and taught words. Eventually, the chimpanzees might get to a two-year-old human's list of words, but no further. Vicki was eventually trained to speak four words. The experiments with those chimpanzees did not demonstrate the existence of the faculties shown by Sarah discussed below, in her command of a language, for example. In other experiments, other chimpanzees have been taught American Sign Language (ASL), notably Washoe. Washoe could use 68 gestures after three years of training, eventually getting to 150 gestures. However, Nim, trained in ASL, was found to demonstrate no forms with grammar, his linguistic productions being sets of gestures in no particular order. Koko and Chantek were also trained in ASL. See also Kanzi's 400-word vocabulary of spontaneous productions as of 2005. The language tokens The language consisted of a series of