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Communicating has always been an important human activity. It has been responsible for the development of cultures and their evolution or downfall. Until recently, human communication techniques have been limited to the spoken and written words, sign language and forms of artwork. During the industrial revolution new communication techniques began to evolve. Telegraphs, telephones, radios, photographs, motion pictures and television have all been developed in a relatively brief period of time. Communication equipment and techniques are still being developed and improved. Although different methods of communication have been studied for many years, it has only been recently that the process of communicating itself has come under study.