Kanzi, the bonobo chimp, is one of many examples illustrating ability for animal language. Kanzi’s mother was in a language learning study, and was taught to communicate via symbols on a computer (lexigrams). Researchers were not trying to teach Kanzi as he was a baby at the time, but he was present with his mother during the study. Later, researchers decided to test Kanzi as well, who ended up performing better than his mother. With much training, Kanzi was able to perform as well as Alia, an untrained two-year old girl (Figure 1 below). However, he was never able to develop the language skills of a five or six-year-old.
Figure 1. Task comparison between Kanzi and Alia.
Children are able to grasp vast amounts of psycholinguistic knowledge. For example, babbling occurs in the four to ten month old range. A great amount of phonological development takes place in their first year. One-year-old infants can discriminate all phonemes of all languages. However, these discriminations are gradually lost if they are not important to the native language. During their first year, infants reach the one-word stage. By age two, they are at the two-word stage. Past two years, language rapidly develops into complete sentences. By age five, kids know up to 15,000 words.
However, this rapid learning occurs only during the critical period. Those that learn a language past the age of ten to twelve never gain native ability. Learners of non-verbal language, such as sign language, also show critical period effects. Drastic problems of language can result in those that were raised in social isolation, to where they never learn language with native ability. Even more extreme linguistic impairment can result due to brain damage. Since there are not very many animal models for language, much was learned from studies of patients with brain damage and from neuroimaging studies.
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