Patterson, F. 1991. Self-awareness in the gorilla Koko. Gorilla 14(2), 2-5.

Responses of an adult female gorilla (Koko) to her own mirror reflections are described, documented and analyzed. During every session, Koko frequently exhibited self-directed behaviors such as grooming her underarms and picking at her teeth with the aid of the mirror ... or using the mirror to inspect a spot on her cheek. ... The evidence provided by the mirror study combined with that provided by Koko's linguistic abilities leaves little doubt that she is capable of self-recognition and is self-aware.