Communication
Communication (from , meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquiry studying them. There are many disagreements about its precise definition. John Peters argues that the difficulty of defining communication emerges from the fact that communication is both a universal phenomenon and a specific discipline of institutional academic study. One definitional strategy involves limiting what can be included in the category of communication (for example, requiring a "conscious intent" to persuade). By this logic, one possible definition of communication is the act of developing meaning among entities or groups through the use of sufficiently mutually understood signs, symbols, and semiotic conventions.

An important distinction is between verbal communication, which happens through the use of a language, and non-verbal communication, for example, through gestures or facial expressions. Models of communication try to provide a detailed explanation of the different steps and entities involved. An influential model is given by Claude Shannon and Warren Weaver, who argue that communicative motivation prompts the sender to compose a message, which is then encoded and transmitted. Once it has reached its destination, it is decoded and interpreted by the receiver.Fiske, John (1982): Introduction to Communication Studies. London: RoutledgeShannon, Claude E. & Warren Weaver (1949). A Mathematical Model of Communication. Urbana, IL: University of Illinois Press Communication is studied in various fields. Information theory investigates the quantification, storage, and communication of information in general. Communication studies is concerned with human communication, while the science of biocommunication is interested in any form of communication between living organisms.

Communication can be realized visually (through images and written language) and through auditory, tactile/haptic (e.g. Braille or other physical means), olfactory, electromagnetic, or biochemical means (or any combination thereof). Human communication is unique in its extensive use of abstract language.

 Definitions 
Communication is usually understood as the transmission of information. In this regard, a message is conveyed from a sender to a receiver using some form of medium, such as sound, paper, bodily movements, or electricity. In a different sense, the term "communication" can also refer just to the message that is being communicated or to the field of inquiry studying such transmissions. There is a lot of disagreement concerning the precise characterization of communication and various scholars have raised doubts that any single definition can capture the term accurately. These difficulties come from the fact that the term is applied to diverse phenomena in different contexts, often with slightly different meanings. Despite these problems, the question of the right definition is of great theoretical importance since it affects the research process on all levels. This includes issues like which empirical phenomena are observed, how they are categorized, which hypotheses and laws are formulated as well as how systematic theories based on these steps are articulated. The word "communication" has its root in the Latin verb "communicare", which means "to share" or "to make common".

Some theorists give very broad definitions of communication that encompass unconscious and non-human behavior. In this regard, many animals communicate within their own species and even plants like flowers may be said to communicate by attracting bees. Other researchers restrict communication to conscious interactions among human beings. Some definitions focus on the use of symbols and signs while others emphasize the role of understanding, interaction, power, or transmission of ideas. Various characterizations see the communicator's intent to send a message as a central component. On this view, the transmission of information is not sufficient for communication if it happens unintentionally. An important version of this view is given by Paul Grice, who identifies communication with actions that aim to make the recipient aware of the communicator's intention. One question in this regard is whether only the successful transmission of information should be regarded as communication. For example, distortion may interfere and change the actual message from what was originally intended. A closely related problem is whether acts of deliberate deception constitute communication.

According to an influential and broad definition by I. A. Richards, communication happens when one mind acts upon its environment in order to transmit its own experience to another mind. Another important characterization is due to Claude Shannon and Warren Weaver. On their view, communication involves the interaction of several components, such as a source, a message, an encoder, a channel, a decoder, and a receiver. The paradigmatic form of communication happens between two or several individuals. However, it can also take place on a larger level, for example, between organizations, social classes, or nations. Niklas Luhmann rejects the view that communication is, on its most fundamental level, an interaction between two distinct parties. Instead, he holds that "only communication can communicate" and tries to provide a conceptualization in terms of autopoietic systems without any reference to consciousness or life. John Peters sees communication as "an apparent answer to the painful divisions between self and other, private and public, and inner thought and outer world."

Communication models

Models of communication are conceptual representations of the process of communication. Their goal is to provide a simplified overview of its main components. This makes it easier for researchers to formulate hypotheses, apply communication-related concepts to real-world cases, and test predictions. However, it is often argued that many models lack the conceptual complexity needed for a comprehensive understanding of all the essential aspects of communication. They are usually presented visually in the form of diagrams showing various basic components and their interaction.

Models of communication are often categorized based on their intended applications and how they conceptualize communication. Some models are general in the sense that they are intended for all forms of communication. They contrast with specialized models, which aim to describe only certain forms of communication, like models of mass communication. An influential classification distinguishes between linear transmission models, interaction models, and transaction models. Linear transmission models focus on how a sender transmits information to a receiver. They are linear because this flow of information only goes in one direction. This view is rejected by interaction models, which include a feedback loop. Feedback is required to describe many forms of communication, such as a regular conversation, where the listener may respond by expressing their opinion on the issue or by asking for clarification. For interaction models, communication is a two-way-process in which the communicators take turns in sending and receiving messages. Transaction models further refine this picture by allowing sending and responding to happen at the same time. This modification is needed, for example, to describe how the listener in a face-to-face conversation gives non-verbal feedback through their body posture and their facial expressions while the other person is talking. Transaction models also hold that meaning is produced during communication and does not exist independent of it.

thumb|upright=1.5|alt=Diagram of Lasswell's model|Lasswell's model is based on five questions corresponding to five basic components.
All the early models, developed in the middle of the 20th century, are linear transmission models. Lasswell's model, for example, is based on five fundamental questions: "Who?", "Says What?", "In What Channel?", "To Whom?", and "With What Effect?". The goal of these questions is to identify the basic components involved in the communicative process: the sender, the message, the channel, the receiver, and the effect. Lasswell's model was initially only conceived as a model of mass communication, but it has been applied to various other fields as well. Some theorists have expanded it by including additional questions, like "Under What Circumstances?" and "For What Purpose?".

thumb|upright=1.5|alt=Diagram of the Shannon–Weaver model|The Shannon–Weaver model focuses on how a message is first translated into a signal and then back into a message.
The Shannon–Weaver model is another influential linear transmission model. It is based on the idea that a source creates a message, which is then translated into a signal by a transmitter. Noise may interfere and distort the signal. Once the signal reaches the receiver, it is translated back into a message and made available to the destination. For a landline telephone call, the person calling is the source and their telephone is the transmitter. It translates the message into an electrical signal that travels through the wire, which acts as the channel. The person taking the call is the destination and their telephone is the receiver. The Shannon–Weaver model includes an in-depth discussion of how noise can distort the signal and how successful communication can be achieved despite noise. This can happen, for example, by making the message partially redundant so that decoding is possible nonetheless. Other influential linear transmission models include Gerbner's model and Berlo's model.

thumb|upright=1.5|alt=Diagram of the feedback loop in Schramm's model of communication|Central to Schramm's model are the processes of encoding and decoding as well as feedback.
The earliest interaction model is due to Wilbur Schramm. For him, communication starts when a source has an idea and expresses it in the form of a message. This process is called encoding and happens using a code, i.e. a sign system that is able to express the idea, for example, through visual or auditory signs. The message is sent to a destination, who has to decode and interpret it in order to understand it. In response, they formulate their own idea, encode it into a message and send it back as a form of feedback. Another important innovation of Schramm's model is that previous experience is necessary to be able to encode and decode messages. For communication to be successful, the fields of experience of source and destination have to overlap.

thumb|upright=1.5|alt=Diagram of Barnlund's model of interpersonal communication|Barnlund's model of interpersonal communication. The orange arrows show how the communicators decode cues and the yellow arrows symbolize their behavioral responses.
The first transactional model was proposed by Dean Barnlund. He understands communication as "the production of meaning, rather than the production of messages". Its goal is to decrease uncertainty and arrive at a shared understanding. This happens in response to external and internal cues. Decoding is the process of ascribing meaning to them and encoding consists in producing new behavioral cues as a response.

Human
There are many forms of human communication. Important distinctions concern whether language is used, as in the contrast between verbal and non-verbal communication, and whether one communicates with others or with oneself, as in the contrast between interpersonal and intrapersonal communication. The field studying human communication is known as anthroposemiotics.

Mediums
 Verbal 

Verbal communication refers to the exchange of messages in linguistic form or by means of language. Some of the difficulties in distinguishing verbal from non-verbal communication come from the difficulties in defining what exactly language means. Language is usually understood as a conventional system of symbols and rules used for communication. Important in this regard is that the system is based on a set of simple units of meaning that can be combined with each other to express more complex ideas. The rules for combining the units into compound expressions are called grammar. This way, words are combined to form sentences. One hallmark of human language, in contrast to animal communication, lies in its complexity and expressive power. For example, it can be used to refer not just to concrete objects in the here-and-now but also to spatially and temporally distant objects and to abstract ideas. The academic discipline studying language is called linguistics. Important subfields include semantics (the study of meaning), morphology (the study of word formation), syntax (the study of sentence structure), pragmatics (the study of language use), and phonetics (the study of basic sounds).

An important distinction among languages is between natural and artificial or constructed languages. Natural languages, like English, Spanish, and Japanese, developed naturally and for the most part unplanned in the course of history. Artificial languages, like Esperanto, the language of first-order logic, C++, and Quenya, are purposefully designed from the ground up. Most everyday verbal communication happens using natural languages. The most important forms of verbal communication are speech and writing together with their counterparts of listening and reading. Spoken languages use sounds to produce signs and transmit meaning while for writing, the signs are physically inscribed on a surface. Sign languages, like American Sign Language, are another form of verbal communication. They rely on visual means, mostly by using gestures with hands and arms, to form sentences and convey meaning. In colloquial usage, verbal communication is sometimes restricted to oral communication and may exclude writing and sign languages. However, in the academic sense, the term is usually used in a wider sense and encompasses any form of linguistic communication, independent of whether the language is expressed through speech, writing, or gestures. Humans have a natural tendency to acquire their native language in childhood. They are also able to learn other languages later in life, so-called second languages. But this process is less intuitive and often does not result in the same level of linguistic competence.

Verbal communication serves various functions. One important function is to exchange information, i.e. an attempt by the speaker to make the audience aware of something, usually of an external event. But language can also be used to express the speaker's feelings and attitudes. A closely related role is to establish and maintain social relations with other people. Verbal communication is also utilized to coordinate one's behavior with others and influence them. In some cases, language is not employed for an external purpose but only for entertainment or because it is enjoyable. One aspect of verbal communication that stands out in comparison to non-verbal communication is that it helps the communicators conceptualize the world around them and themselves. This affects how perceptions of external events are interpreted, how things are categorized, and how ideas are organized and related to each other.

 Non-verbal 

Non-verbal communication refers to the exchange of information through non-linguistic modes, like facial expressions, gestures, and postures. However, not every form of non-verbal behavior constitutes non-verbal communication and some theorists hold that the existence of a socially shared coding system for interpreting the meaning of the behavior is relevant for whether it should be regarded as non-verbal communication. A lot of non-verbal communication happens unintentionally and unconsciously, like sweating or blushing. But there are also conscious intentional forms, like shaking hands or raising a thumb. Traditionally, most research focused on verbal communication. However, this paradigm has shifted and a lot of importance is given to non-verbal communication in contemporary research. For example, many judgments about the nature and behavior of other people are based on non-verbal cues, like their facial expressions and tone of voice. Some theorists claim that the majority of the ideas and information conveyed happens this way. According to Ray Birdwhistell, for example, 65% of communication happens non-verbally. Other reasons for its importance are that it is present in almost every communicative act to some extent, that it is able to fulfill many different functions, and that certain parts of it are universally understood. It has also been suggested that human communication is at its core non-verbal and that words can only acquire meaning because of non-verbal communication. The earliest forms of human communication are non-verbal, like crying to indicate distress and later also babbling, which conveys information about the infant's health and well-being. Non-verbal communication is studied in various fields besides communication studies, like linguistics, semiotics, anthropology, and social psychology.

Non-verbal communication has many functions. It frequently contains information about emotions, attitudes, personality, interpersonal relationships, and private thoughts. It often happens simultaneously with verbal communication and helps optimize the exchange through emphasis and illustration or by adding additional information. Non-verbal cues can also clarify the intent behind a verbal message. Communication is usually more effective if several modalities are used and their messages are consistent. But in some cases, the different modalities contain conflicting messages, for example, when a person verbally agrees with a statement but presses their lips together, thereby indicating disagreement non-verbally.

There are many forms of non-verbal communication. They include kinesics, proxemics, haptics, paralanguage, chronemics, and physical appearance. Kinesics investigates the role of bodily behavior in conveying information. It is commonly referred to as body language, even though it is, strictly speaking, not a language but belongs to non-verbal communication. It includes many forms, like gestures, postures, walking styles, and dance. Facial expressions, like laughing, smiling, and frowning, are an important part of kinesics since they are both very expressive and highly flexible. Oculesics is another subcategory of kinesics in regard to the eyes. It covers questions like how eye contact, gaze, blink rate, and pupil dilation form part of communication. Some kinesic patterns are inborn and involuntary, like blinking, while others are learned and voluntary, like giving a military salute. Proxemics studies how personal space is used in communication. For example, the distance between the speakers reflects their degree of familiarity and intimacy with each other as well as their social status. Haptics investigates how information is conveyed using touching behavior, like handshakes, holding hands, kissing, or slapping. Many of the meanings associated with haptics reflect care, concern, anger, and violence. For example, handshaking is often seen as a symbol of equality and fairness, while refusing to shake hands can indicate aggressiveness. Kissing is another form often used to show affection and erotic closeness.

Paralanguage, also known as vocalics, concerns the use of voice in communication. It depends on verbal communication in the form of speech but studies how something is said instead of what is said. It includes factors like articulation, lip control, rhythm, intensity, pitch, fluency, and loudness. In this regard, saying something loudly and in high pitch may convey a very different meaning than whispering the same words. Paralanguage is mainly concerned with spoken language but also includes aspects of written language, like the use of colors and fonts as well as the spatial arrangement in paragraphs and tables. Chronemics refers to the use of time, for example, what messages are sent by being on time or being late for a meeting. The physical appearance of the communicator also carries a lot of information, like height, weight, hair, skin color, gender, odors, clothing, tattooing, and piercing. It is an important factor for first impressions but is more limited as a mode of communication since it is less changeable. Some forms of non-verbal communication happen using artifacts, such as drums, smoke, batons, or traffic lights.

 Channels 
For communication to be successful, the message has to travel from the sender to the receiver. The term channel refers to the way this is accomplished. In this regard, the channel is not concerned with the meaning of the message but only with the technical means of how the meaning is conveyed. Channels are often understood in terms of the senses used to perceive the message, i.e. hearing, seeing, smelling, touching, and tasting. But in the widest sense, channels encompass any form of transmission, including technological means like books, cables, radio waves, telephones, or television. Naturally transmitted messages usually fade rapidly whereas many messages using artificial channels have a much longer lifespan, like books or sculptures.

The physical characteristics of a channel have an important impact on the code and cues that can be used to express the information. For example, telephone calls are restricted to the use of verbal language and paralanguage but exclude facial expressions. It is often possible to translate messages from one code into another to make them available to a different channel, for example, by writing down words instead of speaking them or by using sign language. For many technical purposes, the choice of channels matters regarding the amount of information that can be transmitted. For example, a wired Ethernet connection may have a higher capacity for data transfer than a wireless WiFi connection, making it more suitable for transferring large amounts of data. The same is true for fiber optic cables in contrast to copper cables.

The transmission of information can occur through multiple channels at once. For example, regular face-to-face communication combines the auditory channel to convey verbal information with the visual channel transmitting non-verbal information using gestures and facial expressions. Employing multiple channels can enhance the effectiveness of communication by helping the audience better understand the subject matter. The choice of channels often matters since the receiver's ability to understand may vary depending on the chosen channel. For example, a teacher may decide to present some information orally and other information visually, depending on the content and the student's preferred learning style.

 Interpersonal 
Interpersonal communication refers to communication between distinct individuals. Its typical form is dyadic communication between two people but it can also refer to communication within groups. It can be planned or unplanned and occurs in many different forms, like when greeting someone, during salary negotiations, or when making a phone call. Some theorists understand interpersonal communication as a fuzzy concept that manifests in degrees. On this view, an exchange is more or less interpersonal depending on how many people are present, whether it happens face-to-face rather than through telephone or email, and whether it focuses on the relationship between the communicators. In this regard, group communication and mass communication are less typical forms of interpersonal communication and some theorists treat them as distinct types.

Various theories of the function of interpersonal communication have been proposed. Some focus on how it helps people make sense of their world and create society while others hold that its primary purpose is to understand why other people act the way they do and to adjust one's behavior accordingly. A closely related approach is to focus on information and see interpersonal communication as an attempt to reduce uncertainty about others and external events. Other explanations understand it in terms of the needs it satisfies. This includes the needs of belonging somewhere, being included, being liked, maintaining relationships, and influencing the behavior of others. On a practical level, interpersonal communication is used to coordinate one's actions with the actions of others in order to get things done. Research on interpersonal communication concerns various topics, such as how people build, maintain, and dissolve relationships through communication, why they choose one message rather than another, what effects these messages have on the relationship and on the individual, and how to predict whether two people would like each other.

Interpersonal communication can be synchronous or asynchronous. For asynchronous communication, the different parties take turns in sending and receiving messages. An example would be the exchange of letters or emails. For synchronous communication, both parties send messages at the same time. This happens, for example, when one person is talking while the other person sends non-verbal messages in response signaling whether they agree with what is being said. Some theorists distinguish between content messages and relational messages. Content messages express the speaker's feelings toward the topic of discussion. Relational messages, on the other hand, demonstrate the speaker's feelings toward their relationship with the other participants.

 Intrapersonal 
Intrapersonal communication refers to communication with oneself. In some cases this manifests externally, like when engaged in a monologue, taking notes, highlighting a passage, and writing a diary or a shopping list. But many forms of intrapersonal communication happen internally in the form of inner dialog, like when thinking about something or daydreaming. 

Intrapersonal communication serves various functions. As a form of inner dialog, it is usually triggered by external events and may happen in the form of articulating a phrase before expressing it externally, planning for the future, or as an attempt to process emotions when trying to calm oneself down in stressful situations. It can help regulate one's own mental activity and outward behavior as well as internalize cultural norms and ways of thinking. External forms of intrapersonal communication can aid one's memory, like when making a shopping list, help unravel difficult problems, as when solving a complex mathematical equation line by line, and internalize new knowledge, like when repeating new vocabulary to oneself. Because of these functions, intrapersonal communication can be understood as "an exceptionally powerful and pervasive tool for thinking."

Based on its role in self-regulation, some theorists have suggested that intrapersonal communication is more fundamental than interpersonal communication. This is based on the observation that young children sometimes use egocentric speech while playing in an attempt to direct their own behavior. On this view, interpersonal communication only develops later when the child moves from their early egocentric perspective to a more social perspective. Other theorists contend that interpersonal communication is more basic. They explain this by arguing that language is used first by parents to regulate what their child does. Once the child has learned this, it can apply the same technique on itself to get more control over its own behavior.

 Contexts and purposes 
There are countless other categorizations of communication besides the types discussed so far. They often focus on the context, purpose, and topic of communication. For example, organizational communication concerns communication between members of organizations such as corporations, nonprofits, or small businesses. Important in this regard is the coordination of the behavior of the different members as well as the interaction with customers and the general public. Closely related terms are business communication, corporate communication, professional communication, and workspace communication. Political communication refers to communication in relation to politics. It covers topics like electoral campaigns to influence the voters and legislative communication, like letters to a congress or committee documents. Specific emphasis is often given to propaganda and the role of mass media. Intercultural communication is relevant to both organizational and political communication since they often involve attempts to exchange messages between communicators from different cultural backgrounds. Important in this regard is to avoid misunderstandings since the cultural background affects how messages are formulated and interpreted. This is also relevant for development communication, which is concerned with the use of communication for assisting in development, specifically concerning aid given by first-world countries to third-world countries. Another important field is health communication, which is about communication in the field of healthcare and health promotion efforts. An important topic in this field is how healthcare providers, like doctors and nurses, should communicate with their patients.

Many other types of communication are discussed in the academic literature. They include international communication, non-violent communication, strategic communication, military communication, aviation communication, risk communication, defensive communication, upward communication, interdepartmental communication, scientific communication, environmental communication, and agricultural communication.

Non-human

Besides human communication, there are also many forms of non-human communication found, for example, in the animal kingdom and among plants. Sometimes, the term extrapersonal communication is used in this regard to contrast it with interpersonal and intrapersonal communication. The field of inquiry studying non-human communication is called biosemiotics. There are additional difficulties in this field for judging whether communication has taken place between two individuals. For example, acoustic signals are often easy to notice and analyze for scientists but additional difficulties come when judging whether tactile or chemical changes should be understood as communicative signals rather than as other biological processes.

For this reason, researchers often use slightly altered definitions of communication in order to facilitate their work. A common assumption in this regard comes from evolutionary biology and holds that communication should somehow benefit the communicators in terms of natural selection. In this regard, "communication can be defined as the exchange of information between individuals, wherein both the signaller and receiver may expect to benefit from the exchange." So the sender should benefit by influencing the receiver's behavior and the receiver should benefit by responding to the signal. It is often held that these benefits should exist on average but not necessarily in every single case. This way, deceptive signaling can also be understood as a form of communication. One problem with the evolutionary approach is that it is often very difficult to assess the influence of such behavior on natural selection. Another common pragmatic constraint is to hold that it is necessary to observe a response by the receiver following the signal when judging whether communication has occurred.

Animals
Animal communication refers to the process of giving and taking information among animals. The field studying animal communication is called zoosemiotics. There are many parallels to human communication. For example, humans and many animals express sympathy by synchronizing their movements and postures. Nonetheless, there are also important differences, like the fact that humans also engage in verbal communication while animal communication is restricted to non-verbal communication. Some theorists have tried to distinguish human from animal communication based on the claim that animal communication lacks a referential function and is thus not able to refer to external phenomena. However, this view is often rejected, especially for higher animals. A different approach is to draw the distinction based on the complexity of human language, especially its almost limitless ability to combine basic units of meaning into more complex meaning structures. For example, it has been argued that recursion is a property of human language that sets it apart from all non-human communicative systems. Another difference is that human communication is frequently associated with a conscious intention to send information, which is often not discernable for animal communication.

Animal communication can take a variety of forms, including visual, auditory, tactile, olfactory, and gustatory communication. Visual communication happens in the form of movements, gestures, facial expressions, and colors, like movements seen during mating rituals, the colors of birds, and the rhythmic light of fireflies. Auditory communication takes place through vocalizations by species like birds, primates, and dogs. It is frequently used to alert and warn. Lower animals often have very simple response patterns to auditory messages, reacting either by approach or avoidance. More complex response patterns are observed for higher species, which may use different signals for different types of predators and responses. For example, certain primates use different signals for airborne and land predators. Tactile communication occurs through touch, vibration, stroking, rubbing, and pressure. It is especially relevant for parent-young relations, courtship, social greetings, and defense. Olfactory and gustatory communication happens chemically through smells and tastes. 

There are huge differences between species concerning what functions communication plays, how much it is realized, and the behavior through which they communicate. Common functions include the fields of courtship and mating, parent-offspring relations, social relations, navigation, self-defense, and territoriality. An important part of courtship and mating consists in identifying and attracting potential mates. This can happen through songs, like grasshoppers and crickets, chemically through pheromones, like moths, and through visual messages by flashing light, like fireflies. For many species, the offspring depends for its survival on the parent. One central function of parent-offspring communication is to recognize each other. In some cases, the parents are also able to guide the offspring's behavior. Social animals, like chimpanzees, bonobos, wolves, and dogs, engage in various forms of communication to express their feelings and build relations. Navigation concerns the movement through space in a purposeful manner, e.g. to locate food, avoid enemies, and follow a colleague. In bats, this happens through echolocation, i.e. by sending auditory signals and processing the information from the echoes. Bees are another often-discussed case in this respect since they perform a dance to indicate to other bees where flowers are located. In regard to self-defense, communication is used to warn others and to assess whether a costly fight can be avoided. Another function of communication is to mark and claim certain territories used for food and mating. For example, some male birds claim a hedge or part of a meadow by using songs to keep other males away and attract females.

Two competing theories in the study of animal communication are nature theory and nurture theory. Their conflict concerns to what extent animal communication is programmed into the genes as a form of adaptation rather than learned from previous experience as a form of conditioning. To the degree that it is learned, it usually happens through imprinting, i.e. as a form of learning that only happens in a certain phase and is then mostly irreversible.

Plants, fungi, and bacteria
Plant communication refers to plant processes involving the sending and receiving of information. The field studying plant communication is called phytosemiotics. This field poses additional difficulties for researchers since plants are very different from humans and other animals: they lack a central nervous system and have rigid cell walls. These walls restrict movement and make it impossible for plants to send or receive signals that depend on rapid movement. However, there are important similarities as well since plants face many of the same challenges as other animals, like finding resources, avoiding predators and pathogens as well as finding mates and ensuring that their offspring survives. Many of the evolutionary responses to these challenges are analogous to those in animals but are implemented using different means. One important difference is that chemical communication is much more prominent for plant communication in contrast to the importance of visual and auditory communication for animals.

thumb|upright=1.5|alt=Diagram of the steps of plant communication|Steps of plant communication
Communication is a form of behavior. In regard to plants, the term behavior is usually not defined in terms of physical movement, as is the case for animals, but as a biochemical response to a stimulus. This response has to be short relative to the plant's lifespan. Communication is a special form of behavior that involves conveying information from a sender to a receiver and is distinguished from other types of behavior, like defensive reactions and mere sensing. Theorists usually include additional requirements, like that there is some form of response in the receiver and that the communicative behavior benefits both sender and receiver in terms of natural selection. Richard Karban distinguishes three steps of plant communication: the emission of a cue by a sender, the perception of the cue by a receiver, and their response. It is not relevant to what extent the emission of a cue is intentional but it should be possible for the receiver to ignore the signal.

Plant communication happens in various forms. It includes communication within plants, i.e. within plant cells and between plant cells, between plants of the same or related species, and between plants and non-plant organisms, especially in the root zone. Plant roots also communicate with rhizome bacteria, fungi, and insects within the soil. A prominent form of communication is airborne and happens through so-called volatile organic compounds (VOCs). For example, many plants, like maple trees, release VOCs when they are attacked by a herbivore to warn neighboring plants, which then react accordingly by adjusting their defenses. Another form of plant-to-plant communication happens through mycorrhizal fungi. These fungi form underground networks, sometimes referred to as the Wood-Wide Web, and connect the roots of different plants. The plants use the network to send messages to each other, specifically to warn other plants of a pest attack and to help prepare their defenses.

Communication can also be observed for fungi and bacteria. Some fungal species communicate by releasing pheromones into the external environment. For example, they are used to promote sexual interaction (mating) in several aquatic fungal species, like Allomyces macrogynus, the Mucorales fungus Mucor mucedo, Neurospora crassa and the yeasts Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Rhodosporidium toruloides.O'Day, D.H. (1981). Modes of cellular communicatin and sexual interactions in eukaryotic microbes.  In: Sexual Interactions in Eukaryotic Microbes. (O'Day, D.H. & Horgen, P.A., eds), pp. 3-17. New York: Academic Press An important form of communication between bacteria is called quorum sensing. It happens by releasing hormone-like molecules, which other bacteria detect and respond to. This process is used to monitor the environment for other bacteria and to coordinate population-wide responses, for example, by sensing the density of bacteria and regulating gene expression accordingly. Other possible responses include the induction of bioluminescence and the formation of biofilms.

 Interspecies 
Most communication happens between members within a species as a form of intraspecies communication. This is because the purpose of communication is usually some form of cooperation, which happens mostly within a species while different species are often in conflict with each other in their competition over resources. However, there are also some forms of interspecies communication. This occurs especially when there are symbiotic relationships and significantly less for parasitic or predator-prey relationships.

Interspecies communication plays an important role for various plants that depend for their reproduction on external agents. For example, flowers need insects for pollination and provide resources like nectar and other rewards in return. They use various forms of communication to signal their benefits and attract visitors, for example, by using colors that stand out from their surroundings and by using symmetrical shapes. This form of advertisement is necessary since different flowers compete for potential visitors. Many fruit-bearing plants rely on plant-to-animal communication to disperse their seeds and move them to a favorable location. This happens by providing nutritious fruits to animals. The seeds are eaten together with the fruit and are later excreted at a different location. Communication is central to make the animals aware of where the fruits are and whether they are ripe. For many fruits, this happens through their color: they have an inconspicuous green color until they ripen and take on a new color that stands in visual contrast to the environment. Another example of interspecies communication is found in the ant-plant relationship. It concerns, for example, the selection of seeds by ants for their ant gardens and the pruning of exogenous vegetation as well as plant protection by ants.

Several animal species also engage in interspecies communication, like apes, whales, dolphins, elephants, and dogs. For example, different species of monkeys use common signals to cooperate when threatened by a common predator. An example of interspecies communication involving humans is found in their relation to pets. For example, acoustic signals play a central role in communication with dogs. Dogs are able to learn to respond to various commands, like "sit" and "come". They can even learn short syntactic combinations, like "bring X" or "put X in a box". They also react to the pitch and frequency of the human voice by reading off information about emotions, dominance, and uncertainty. Humans can understand dog signals in the form of interpreting and reacting to their emotions, such as aggressiveness, fearfulness, and playfulness.

Communication studies

Communication studies, also referred to as communication science, is the academic discipline studying communication. It is closely related to semiotics, with one difference being that communication studies focuses more on technical questions of how messages are sent, received, and processed while semiotics tackles more abstract questions in relation to meaning and hows signs acquire meaning. Communication studies covers a wide area overlapping with many other disciplines, such as biology, anthropology, psychology, sociology, linguistics, media studies, and journalism. 

Many contributions in the field of communication studies focus on developing models and theories of communication. Models of communication aim to give a simplified overview of the main components involved in communication. Theories of communication, on the other hand, try to provide conceptual frameworks to accurately present communication in all its complexity. Other topics in communication studies concern the function and effects of communication, like satisfying physiological and psychological needs and building relationships as well as gathering information about the environment, others, and oneself. A further issue concerns the question of how communication systems change over time and how these changes correlate with other societal changes. A related question focuses on psychological principles underlying those changes and the effects they have on how people exchange ideas.

Communication was already studied as early as Ancient Greek. Important early theories are due to Plato and Aristotle, who gave a lot of emphasis on the role of public speaking. For example, Aristotle held that the goal of communication is to persuade the audience. However, the field of communication studies only became a separate research discipline in the 20th century, especially starting in the 1940s. The development of new communication technologies, such as telephone, radio, newspapers, television, and the internet, has had a big impact on communication and communication studies. Today, communication studies is a wide discipline that includes many subfields dedicated to topics like interpersonal and intrapersonal communication, verbal and non-verbal communication, group communication, organizational communication, political communication, intercultural communication, mass communication, persuasive communication, and health communication. Some works in communications studies try to provide a very general characterization of communication in the widest sense while others attempt to give a precise analysis of a specific form of communication.

Barriers to effectiveness
Barriers to effective communication can distort the message or intention of the message being conveyed. This may result in failure of the communication process or cause an effect that is undesirable. These include filtering, selective perception, information overload, emotions, language, silence, communication apprehension, gender differences and political correctness.Robbins, S., Judge, T., Millett, B., & Boyle, M. (2011). Organisational Behaviour. 6th ed. Pearson, French's Forest, NSW pp. 315–317.

Noise
In any communication model, noise is interference with the decoding of messages sent over the channel by an encoder. To face communication noise, redundancy and acknowledgement must often be used. Acknowledgements are messages from the addressee informing the originator that his/her communication has been received and is understood.North Atlantic Treaty Organization, NATO Standardization Agency AAP-6 – Glossary of terms and definitions, p. 43. Message repetition and feedback about message received are necessary in the presence of noise to reduce the probability of misunderstanding.

The act of disambiguation regards the attempt of reducing noise and wrong interpretations, when the semantic value or meaning of a sign can be subject to noise, or in presence of multiple meanings, which makes the sense-making difficult. Disambiguation attempts to decrease the likelihood of misunderstanding. This is also a fundamental skill in communication processes activated by counselors, psychotherapists, interpreters, and in coaching sessions based on colloquium. In Information Technology, the disambiguation process and the automatic disambiguation of meanings of words and sentences has also been an interest and concern since the earliest days of computer treatment of language.Nancy Ide, Jean Véronis. "Word Sense Disambiguation: The State of the Art", Computational Linguistics, 24(1), 1998, pp. 1–40.

Cultural aspects
Cultural differences exist within countries (tribal/regional differences, dialects and so on), between religious groups and in organisations or at an organisational level – where companies, teams and units may have different expectations, norms and idiolects. Families and family groups may also experience the effect of cultural barriers to communication within and between different family members or groups. For example: words, colours and symbols have different meanings in different cultures. In most parts of the world, nodding your head means agreement, shaking your head means "no", but this is not true everywhere.Nageshwar Rao, Rajendra P. Das, Communication skills, Himalaya Publishing House, 9789350516669, p. 48

Communication to a great extent is influenced by culture and cultural variables. Understanding cultural aspects of communication refers to having knowledge of different cultures in order to communicate effectively with cross culture people. Cultural aspects of communication are of great relevance in today's world which is now a global village, thanks to globalisation. Cultural aspects of communication are the cultural differences which influence communication across borders. So in order to have an effective communication across the world it is desirable to have a knowledge of cultural variables effecting communication.

According to Michael Walsh and Ghil'ad Zuckermann, Western conversational interaction is typically "dyadic", between two particular people, where eye contact is important and the speaker controls the interaction; and "contained" in a relatively short, defined time frame. However, traditional Aboriginal conversational interaction is "communal", broadcast to many people, eye contact is not important, the listener controls the interaction; and "continuous", spread over a longer, indefinite time frame.

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Further reading

 Fogel, A., Nwokah, E., Dedo, J.Y., Messinger, D., Dickson, K.L., Matusov, E. and Holt, S.A., 1992. Social process theory of emotion: A dynamic systems approach. Social Development, 1(2), pp.122-142.
 

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Category:Communication studies
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