Animals to communicate with humans use animal language. The animal language is a modified version of early human language itself only that animals lack complexity and are less expressive. Great ape language is a means to communicate among apes such as bonobos, orangutans, chimpanzees, and gorillas. Humans communicate with these animals using sign language, lexigrams, yerkish and physical tokens. Jacques Vauclair, Francine Patterson and David Premack are well-known researchers in great ape language.
Humans have used sign language since a very long time. One of the important sign language used by humans is American Sign Language. Animals also use signs to express their feelings and for communication sake. Vocabulary words have been taken from American Sign Language to communicate with the apes. Lexigrams are symbols, which represent something. The symbols are laid down on a flat board called the lexigram board. The lexigram board has three panels with three hundred and eighty four keys. These boards are especially used to communicate with chimpanzees and bonobos. Yerkish also involves keyboard with punch keys, which have the lexigram symbols. It is actually an artificial language. Computer keyboards are also used to aid animals as most of them can be easily trained for keyboard operation.
Plastic tokens are also used for communication with apes. The apes select a specific token when they want to communicate something. The animal is given training to select the right token. Tokens have symbols or pictures. Not all the apes learn this method of communication properly. During the training, the animal is made to learn by rewarding them upon an achievement.
Although animals lack vocal cords and speech organs like humans, some animals have vocals of their own. Wild apes are known to talk to each other to make the other aware of a possible danger. Animal language does not have discreteness like human languages. In human languages, discrete units are combined together to make a new word with a meaning. So signs or sounds, in animal language, cannot be combined to form another sign or sound, which means something. But researchers have proved it that the animal language does meet certain requirements. But the validity is still disputed upon by many and that is the reason why animal language hasn't been given the status of a true language.
People have questioned the practice of great ape language. The researchers try to understand whether the usage of this language aid the animals to solve the problem better. Also, whether the teaching experiences with a primate can be of use when human children are taught. This is because, there is without doubt a difference in the ability of the animal and a human, while they may be similar at some level. Some say that the apes do not actually understand the language, but instead do a clever trick to get a reward. Also some researches say that the signed gesture do not make a grammatically right sentence. The arbitrariness is sometimes missing, that is, there is no clear relationship between the signs or sounds.
Many animals have behaviors, which is similar what we speak. They can understand the language, they can also use it to reflect their thoughts and communicate with a human. Other than primates, animals such as sea lions and dolphins also use sign language and vocals to communicate with human.