In the book, The Education of Koko, by Dr. Penny Patterson and Eugene Linden, Penny says:
“Then, some mornings, she sits on a chair before an electric teletype keyboard in the kitchen for a thirtyminute lesson in the production of English. Gorillas cannot generate the sounds necessary to speak, but through this Auditory Language keyboard, which is linked to a voice synthesizer, we have given Koko a device that enables her to talk as well as generate signs, Other morning we videotape or audiotape or work with flashcards."

The following video clip gives you a sense of how a "talking teletype" helped Koko vocalize her words. When she was older, Apple Computer gave her an updated device — one of the first touchscreen computers.

However, generally speaking, Koko preferred to use Sign Language over a keyboard ...