Background: The reserchers were investigating whether pygmy chimps could spontaneously use symbols to communicate with people. They found that unlike common chimps, the pygmy chimps could acquire the use of symbols by observing others use these symbols in everyday communications without any explicit training. Furthermore, researchers demonstrated that pygymy chimps were beginning to comprehend English words and identify lexigrams when they heard the spoken words. The common chimps were unable to do this. Previous research carried out by Gardner and Gardner also demonstrated the ability of chimps acquiring language. E.g. the Gardners demonstrated that Washoe, a common chimp, could produce symbols, such as sign langugge, to bring about a change, such as asking for a tickle. They taught Washoe American Sign Language, but they didn't teach chimps to talk because they don't have the vocal chords as language comprehension involves more than just responding to words. This type of learning is called Associative Symbol Learning (ASL). ASL occurs when an individal learn to associate specific symbols with specific objects e.g. naming pictures in a book. It has also been demonstrated that when chimps are systematically taught how to request, label and comprehend objects that a more sophisticated type of learnign can appear. E.g. Savage-Rumbaugh demonstrated that 2 common chimps (Austin and Sherman) were able to use Representational (referential) symbol learning (RSL). RSL occurs when an individual can refer to objects where there are no contextual cues to provide association. E.g. being able to respond to the request "get your ball" even if the ball is in another room. The foucs of the present study was language comprehension, rather than language production. The researchers believed that if the chimps could understand spoken language without any formal training, and do more than respond to a cue, then this would suggest they have similar language abilities to humans.