 Research with captive grey parrots, especially Irene Pepperberg's work with an individual named Alex, has demonstrated they possess the ability to associate simple human words with meanings, and to intelligently apply the abstract concepts of shape, colour, number, zero-sense, etc.According to Pepperberg and other scientists, they perform many cognitive tasks at the level of dolphins, chimpanzees, and even human toddlers.Another notable African grey is N'kisi, which in 2004 was said to have a vocabulary of over 950 words which she used in creative ways.