The Hayes' experiment with Vicki

The film

The star

Vicki was common chimpanzee raised by the psychologists Keith and Catherine Hayes in their home for about seven years. She is the third such "experiment" that I know of -- Nadia Kohts and Joni, the Kellogg's and Gua.-- being the first two. Keith Hayes at the time worked at the Yerkes lab in Orange, FL.

A number of films, articles, and books have been published about Vicki. Catherine Hayes (1951) wrote the popular "The ape in our House" that gives many details of Vicki's growth and adaptation to a human family environment


It is likely that Vicki inspired the Bonzo Hollywood films. Compare the dialogue in "Bonzo" with Catherine Hayes (1951). "Does a child mature into intelligence bit by bit as decreed by his heredity? Or does he acquire intelligence through experience in his social and physical environment?…We believe that by substituting a home raised ape for one of the subjects and by equating its environment with the child's we would see the working of a greater difference in heredity than exists between any two children. We have shown in actual fact that Vicki's education caused her to resemble the child considerably at eighteen months. Those ways that she differed could now be fairly attributed to her anthropoid heredity. P.95.


"The significance of Vicki's speech training lies not in the fact that she learned a few words (JL, maybe three Mama, Papa, cup) , but rather in her great difficulty in doing so, and in keeping them straight afterward." (C. Hayes, 1951, p 241

Indeed, all these home-raised studies come to the same conclusions: apes and humans are fairly similar until age two other than in regards to language. In regards language, while there is substantial comprehension of human language, there is absolutely no evidence of its production. The idea of a "Language Instinct" (Pinker, 1994) gains strong support from these home-raised chimps.


Film contents and comment

Vicki appears to be under lots of stress. She moves side to side nervously and rarely seems relaxed. She is always "on stage" and rarely performs successfully. She seems unable to utter any type of voluntary or instrumental vocal response.

In one study she is expected to vocalize to open a door -- analogous to a Thorndike escape box. It appears she knows what is required and is going through all sorts of gyrations to vocalize but rarely can do it. Any dog would be barking successfully after a few trials -- if not before!

In famous scenes, Vicki is trying to say "Papa" or "cups" and has to resort to using her hands to close her lips to get an unvoiced "puh." If nothing else this indicates that chimps lack the sensori-motor wiring for anything like human speech.

This is no surprise in that brain stimulation studies to elicit vocalization have not shown in non-human primates anything like the results of Penfield and Roberts (1959). These investigators found that human vocalization could be elicited by stimulation on the surface of the human cortex but not in non-human primates. To get vocalization from these species, stimulation in "older" deeper parts of the brain was required. See Limber (1977), and Leyton and Sherrington (1917).

There is also evidence that food rewards were widely used; it is my (JL) guess that these are counterproductive, maybe destructively interfering with any possible instrumental use of vocalization.


Hayes, C. (1951). The ape in our house. New York, Harper.

Hayes, K.J. and Hayes, C (1952). Imitation in a home-raised chimpanzee. Journal of Comparative and Physiological Psychology, 45, 450-459.

Hayes, K.J. and Nissen, C.H. (1971). Higher mental functions of a home-raised chimpanzee. In Schrier, A.M. and Stollnitz, F. (eds). Behavior of Non-human Primates, Vol. 4, New York, Academic Press, 50-115.

Leyton, A. S. F. and C. S. Sherrington (1917). "Observations on the excitable cortex of the chimpanzee, orangutan, and gorilla." Quarterly Journal of Experimental Physiology 11 135-222.

Limber, J. (1977). "Language in child and chimp?" American Psychologist 32: 280-295 (Reprinted in Sebeok, T. & Sebeok, J. (Eds.) (1980). Speaking of Apes (pp.197-218). New York: Plenum Press.).

(Abstract) Recent successes teaching chimpanzees to engage in symbolic communication have again brought into question the Cartesian supposition that language is uniquely possessed by homo Sapiens. Despite the very remarkable achievements of Washoe and Sarah, an objective comparison of these chimps' linguistic performances with those of a typical 3-year-old child provides scant evidence for rejecting Descartes' view. An organism uses human language if and only if it uses structures characteristic of those languages. The ability of apes or even 2-year olds to communicate and use simple names is NOT sufficient reason to attribute the use of human language to them. The creative or projective aspect of human language cannot be overlooked. Efforts to explain the language of deficits of apes in terms of impoverished language experience, anatomical deficits, or cognitive-structure differences are not convincing.

Penfield, W. and L. Roberts (1959). Speech and brain mechanisms. Princeton, NJ, Princeton University Press.

Pinker, S. (1994). The language instinct. New York, William Morrow and Company.

Thorndike, E. L. (1901). "The mental life of the monkeys." Psychological Monographs 3: 1-57.