memory. Through such cognitive factors Interactive designers can determine for example that a large number of every day users can only be required to remember a few items of information, hence they should not be forced to trawl back through repetitive and distant memories of training programs in order to operate the system. In fact according to Addison Wesley, Human Computer Interaction, the use of cognition led to an increasingly common trick in user interface design, which is to support short term memory by representing additional information on the display or on index cards. This is effectively what a menu does: it provides fast access to a list of commands that do not have to be memories. In contrast, Johnson-Laird, P., (1988) The Computer and the Mind, states that help facilities are regarded, in terms of cognitive design, as a more long-term memory process. We have to load them and trawl through them to find the information that we need. He also states an important example, seven is often regarded as the `magic number' in HCI. We can see this all around us. Important information is kept within the seven-item boundary. For instance, postcodes have up to seven components G12 8QT etc. In some cases, it is necessary to break this rule. In these circumstances, the information is broken up into components with less than seven items. In the United Kingdom, phone number are usually divided in this way, (0141) 339 8855. It follows that users will have difficulty in remembering the contents of menus with over ten items. Command languages with many different options will need additional visual cues if operators are to learn them. Why is seven the magic number? It is as easy for users to hold seven words in short-term memory as it is for them to hold seven unrelated items. Additional information can be held but only if users employ techniques such as chunking. This involves the grouping of information into meaningful sections. It can also in...
