Apple Learning Interchange - KokoTV:
Koko began learning American Sign Language (ASL) from Dr. Penny Patterson when she was only 1 year old. It was supposed to be just a 4-year PhD thesis for Penny, but “personal” bonds developed, and it has become a life-long study/relationship.
Today Koko uses over a thousand words of ASL to express her thoughts and feelings in complex phrases, and she invents new signs as the need arises. She also understands spoken English.
A comprehensive description of Koko’s signing abilities through age 10, with comparisons to human children, can be found in the book: The Education of Koko by Penny Patterson."