2. What are communication media and how do they differ?

Although we often think initially about the physical aspects of communication media (screens, colour, sounds, etc.), the main attribute of a medium is that it provides a language for communication. This language will involve a syntax, semantics, and pragmatics, with the physical aspects of the medium providing constraints on the syntactic possibilities. Traditional computer media have usually been restricted to one sensory channel (e.g. text [visual], graphics [visual], sound [auditory]), but even within one sensory channel, a rich variety of media can be supported. The visual channel, for example, can support graphics, tables, diagrams, pictures, maps, graphical animation, and 3-D graphics, all of which communicate information in different ways. The auditory channel can support speech, verbal gestures, realistic sounds, artificial sounds, and music. The sensory channel can involve vibration and sensory input that might result from, for example, a data glove.

Some information already exists to guide us on the relative claims for different media for effective information transfer. Auditory media, such as radio, make dialogue salient. For example, children given a story in audio only or with a visual + audio combination (same soundtrack) recall dialogue better when it is given as audio only. Television presentation seems to be better for action information, which has improved recall when presented via television [5]. Whilst audio information seems to stimulate imagination, spatial visualization is better handled visually, as might be expected. Other studies have indicated that diagrams are better at conveying ideas, whereas text is better for detail [22]. However, the visual channel does not always dominate. Walker and Scott [24] found that human beings judge light as being of a shorter duration than an identical tone, and when these are presented together, the auditory channel dominates. Pezdek [21] carried out experiments to determine if the visual channel dominated over the auditory channel in the comprehension of information on television. Whilst there was evidence of visual domination, the presence of the auditory channel actually improved comprehension and vice versa.

Text is often better for communicating complex information to experts, whilst pictures are better for exploratory learning. In particular, visual representations are excellent for synthesis. These ideas are shown in figure 1, where the usability of different channels (visual and auditory) is contrasted with the previous knowledge and experience in the knowledge area. For some tasks, text can be a very effective medium of communication. Each different medium of communication, therefore, has properties that will enhance or restrict its capability for transmitting particular types of knowledge.

At a higher level, we can form new media by combining existing ones. When two media are combined, new syntactic and semantic units become possible. These higher level media often use more than one sensory channel. Examples would include movie films and animated diagrams with verbal talk-over. It might be thought that a more complex (or rich) medium would always be preferable to a simpler one, but this is not always so. For example, experiments with televised weather forecasts and radio weather forecasts have shown that the auditory medium is superior in many cases. One can also remember radio plays that are more "vivid" than television plays. As Kosslyn [13] states,

Multimedia technology can deliver information like a fire hose delivers water. Just as drinking from a fire hose is not an efficient way to quench one's thirst, high powered multimedia presentations can overload the senses and fail to communicate information effectively. Multimedia relies on the essential truth in the Chinese proverb that tells us a picture "is worth more than a thousand words." Unfortunately some pictures do not help to control the flow of information, and actually make it worse.

Work on the effectiveness of different media for communicating information has been carried out over many years, but interpretation of the results is not straightforward. Washburne [26] found, for example, that graphs were easier to interpret than tables, whilst Vernon [23] found the opposite. These apparent divergencies are not necessarily surprising. Later work [11, 9] has shown that the usefulness of the different display formats is highly dependent upon the tasks being performed. Effectiveness is dependent upon the nature of the information being sought by the reader.