Humans communicate by thinking of the information they wish to share, encoding it, and transferring it by either verbal, nonverbal or written mediums directly to a receiver who then decodes the information. Communication methods include eye contact, sign language, pictures, writing and sound.
Verbal communication includes listening and speaking a language, and contains non-verbal communication elements, such as posture and facial expression. Public speaking anxiety is experienced by 75 percent of Americans. Nonverbal communication includes clothing, tone of voice, gestures and handwriting style. Nonverbal facial expressions account for 55 percent of human communication. Written communication includes pictographs, alphabets and electronic signals. A zigzag pattern engraved 500,000 years ago by Homo erectus is the oldest known pictogram, as of 2014.
Communication impediments include ambiguity of phrases, physical barriers, individual linguistic ability, cultural differences and attitudinal barriers. Attitudinal barriers refer to the refusal or the delay of communication.
Animals, plants, fungi and bacteria also have communication methods. Animal communication is performed when the behavior of one animal influences the present or future behavior of another animal. Plants can communicate with insects and fungi in the soil using their roots. Plants also communicate via volatiles to warn neighboring plants of herbivores and to attract herbivore parasites. Fungi use molecules to coordinate actions, such as growth, mating and pathogenicity. Bacteria can use quorum sensing to detect the density of cells and adjust its gene expression.