CMC: interactional coherence It is possible for CMC to be simultaneously incoherent and enjoyable because the availability of a persistent textual record of the conversation renders the interaction cognitively manageable, hence offsetting the major "negative" effect of incoherence in spoken interaction. It also opens up possibilities for other types of interaction that go beyond what is available in speech. In this as in other respects, CMC is both "less" and "more" than spoken language—or put another way, it is both dysfunctionally and advantageously incoherent. Two properties of the medium are often cited specifically as obstacles to interaction management: (1)lack of simultaneous feedback, caused by reduced audio-visual cues and the fact that messages cannot overlap; (2)disrupted turn adjacency, caused by the fact that messages are posted in the order received by the system, without regard for what they are responding to. The first property, lack of simultaneous feedback, is a consequence of two separate features of CMC systems. First, text-only CMC is a "lean" medium [15, 16] which relies on fewer channels than face-to-face interaction for transmission of the message. Users do not see or hear their interlocutors and thus do not have access to non-verbal information about how others are responding. Second, most multi-participant CMC systems make use of "one-way" rather than "two-way" transmission—messages are sent in their entirety when the message originator presses 'send' or 'return', rather than one keystroke at a time [8] disrupted turn adjacency, arises from the fact that one-way CMC systems transmit messages linearly, in the order in which they are received by the system. Thus in multi-participant interactions, a message may be separated in linear order from a previous message it is responding to, if another message or messages happen to have been sent in the meantime. overlap of exchanges is rampant in computer-mediated environments. In dyadic communication, users—unable to tell whether their interlocutor is in the process of responding or not—may become impatient and send a second message before a response to the first has been received, resulting in incomplete or interleaved exchange sequences [13, 39]. In group communication, unrelated messages from other participants often intervene between an initiating message and its response, in a likelihood proportional to the number of active participants involved in the communication [8, 37, 45]. there is not a one-to-one correspondence between an initiation and its response. Multiple responses are often directed at a single initiating message, and single messages may respond to more than one initiating message, especially in asynchronous CMC, where longer messages tend to contain multiple conversational moves [5, 14]. Moreover, many initiations receive no response. some participants adopt a strategy of sending out multiple messages in an attempt to attract a response…The overall frequency of multiple initiations may be seen to reflect the difficulty users have in determining others' intentions due to the paucity of feedback in text-only CMC environments. A participant cannot safely assume if he receives no response to a message that this is an intentional communication (e.g., a refusal to engage) on the part of the addressee. The addressee may not have received the message due to technical problems, may not have noticed it if she did receive it (e.g., because it was "buried" among other messages, or because she was away from her terminal when it arrived), or may have tried to return a response but failed for any number of reasons. Redundancy thus compensates for "noise" in the channel (as it does in face-to-face communication), suggesting that the computer medium is "noisy" in regard to turn-taking. [In spoken conversation,] on the local level we find minimal units of conversational structure known as "adjacency pairs" [52] or "exchanges" [55], depending on whether such minimal units are thought to consist of two or three turns. On the global level, extended sequences of related turns comprise "topics" or "discourse topics" [7]… Violations of sequential coherence are the rule rather than the exception in CMC. Adjacency pairs are regularly disrupted by intervening, irrelevant messages, In asynchronous CMC, the task of reconstructing adjacent conversational moves is additionally complicated by the fact that a single message may contain two or more moves which are physically, but not functionally, adjacent [4, 5, 14] Disruptions of extended sequences are also common. The problem of keeping track of topically-related "threads", or sequences of exchanges on a particular topic, is similar to that confronted by the user in tracking single exchanges, only more cognitively challenging. Multiple threads may become entangled, and individual threads are rarely free of disruption by irrelevant messages. In addition, keeping track of longer sequences places a greater burden on users' memories. Perhaps for these reasons, topics decay quickly in computer-mediated discussions, hastened along by off-topic digressions and tangential observations which move the discussion away from its original focus. Empirical research on topic decay (in any communicative modality) is limited. However, some as yet unpublished research supports the perception that topics tend to decay rapidly in computer-mediated groups. In their study of a social chat channel on the Internet, Herring and Nix [30] found that nearly half (47%) of all turns were "off-topic" in relation to the turn to which they were responding. Moreover, the thread of discourse regularly digressed in chains of associatively-related semantic shifts, the only coherence being when the chains were loosely associated with a global topic [26]. Asynchronous discussions also tend towards topic decay. In a study of an Internet discussion list devoted to the 1995 Oklahoma City bombing, Lambiase [35] found that during the first nine days of the list's existence, the percentage of messages on the group's global topic decreased steadily from 65% to 33%. The list met an untimely demise less than a month after it started, Lambiase maintains, largely as a result of disputes over topic management. A tendency for global topics to fragment into competing subtopics was also found for three asynchronous listserv discussion groups studied by Herring [29]. To be sure, topical fragmentation over time is also characteristic of spoken multi-party conversation. However, the tendency is exacerbated in one-way group CMC due to a lack of feedback. Participants compose responses to a topic simultaneously without knowing what (or even that) others are writing; as a result, multiple competing new directions for discussion are introduced. As participants respond to others' responses, the chances that they will move further away from the original topic—and that new topics of discussion will arise—increase exponentially. As Lambiase's study shows, even when computer-mediated groups consciously place a high value on keeping on-topic, "on-topicness" is difficult to enforce. the availability of a persistent textual record of the interaction in most forms of text-only CMC. E-mail leaves a record which must be actively deleted by the user in order to dispose of it, and many listservs archive list discussions. Even in synchronous CMC such as IRC and MUDs, where logs are not automatically kept by the system, users still have the benefit of seeing the immediately preceding interaction preserved on their computer screens for as long as it takes for new messages to cause the old ones to scroll up and off the screen. In this respect, even the least persistent synchronous interface is more persistent than spoken language, which disappears immediately once it is uttered. Persistent conversation aids the user's cognitive processing.