American Sign Language (ASL) was selected by Dr. Penny Patterson as the primary language to teach Koko because of the success that other researchers had with . It turned out to be a good choice, as Koko (and later Michael) learned it quickly. Within just a few weeks the gorillas were using sign combinations. Much later, observations by other researchers at zoos revealed that gorillas seem to have a natural gestural language of their own, using dozens of gestures consistently to communicate with one another (). This may explain why Koko and Michael learned ASL so quickly; it's built on their intrinsic capabilities.
People often ask if gorillas are really using sign symbolically or are mimicking individual signs to "get rewards". Our research shows that gorillas Koko and Michael have used American Sign Language (ASL) in sophisticated ways, with sign phrase lengths of over 8 signs, and consistent grammatical structure. We have published some early papers on the subject (see, for example, "Language Acquisition by a Lowland Gorilla: Koko's First 10 Years", in ) and are now in the process of digitizing and analyzing four decades of data to shed more light on these linguistic questions. Our primary focus, however, is on cognitive questions such as: what can we learn about gorilla thought processes and emotions through two-way communication?
American Sign Language - Berkeley City College
As Koko and Michael were learning American Sign Language, Dr. Patterson always spoke to the gorillas simultaneously while signing to them. Thus, both gorillas learned to comprehend a great deal of spoken English (over 2,000 words for Koko and a similar number for Michael). This is often surprising to people who first meet Koko, and think they can make private side comments to Penny; Koko usually keeps up with the conversation and responds accordingly.