At the time, previous attempts to teach chimpanzees to imitate vocal languages (the Gua and Viki projects) had failed.

The Gardners believed that these projects were flawed because chimpanzees are physically unable to produce the voiced sounds required for oral language.

Much like a human child, she underwent a regular routine with chores, outdoor play, and rides in the family car.

[16] After the first couple of years of the language project, the Gardners and Roger Fouts discovered that Washoe could pick up ASL gestures without direct instruction; she learned by observing humans around her who were signing amongst themselves.

Moreover, the Gardners began to realize that rewarding particular signs with food and tickles—the approach used in operant conditioning—interfered with the learning process.

Kat later remarked that one sign told her more about Washoe and her mental capabilities than all her longer, grammatically perfect sentences.

"[26][27] Primate expert Jane Goodall, who has studied and lived with chimpanzees for decades, believes that this might indicate some level of self-awareness.

[29] Washoe enjoyed playing pretend with her dolls, which she would bathe and talk to and would act out imaginary scenarios.

On October 30, 2007, officials from the Chimpanzee and Human Communication Institute on the CWU campus announced that she had died at the age of 42.

[6][11] Some believe that the fact that Washoe not only communicated, but also formed close and personal relationships with humans indicates that she was emotionally sensitive and deserving of moral status.

[35] Work with Washoe and other signing primates motivated the foundation of the Great Ape Project, which hopes to "include the non-human great apes: chimpanzees, orangutans and gorillas within the community of equals by granting them the basic moral and legal protections that only humans currently enjoy", in order to place them in the moral category of "persons" rather than private property.

[37] This included additional experiments which attempted to teach great apes to communicate in a more controlled environment.

He and Thomas Sebeok argued that the apparently impressive results may have amounted to nothing more than a "Clever Hans" effect.