Design is not only used to attract attention to marketing material but also to make information appear more readable and easier to understand. The way this affects HCI is by designing user interfaces that are easily understood the user is better able to interact with the computer without being confused.

An interaction object has 3 main apsects: state, control, display / presentation. (Control could be subdivided into dispatch, interactors, coordination with other objects.)

 Filling dialogue box once opened, the user can fill in the form in any order, whereas they must follow the menu hierarchy strictly. The form shows all the options at once and leaves them in view, whereas pulldown menus are only visible once opened, and once an option is set it is hidden again. Because of the free order, there must be a special "do it" key in the form, whereas selecting a terminal item on a menu automatically signals completion of the sequence. The error potential is the same: probably no invalid selections will be possible. Feedback is probably the same.

HCI has as a central lesson - that is, we cannot design user interfaces right first time, so we must design iteratively.

There are 5 types of interaction style: command languages (e.g. csh Unix shell), function keys (e.g. OK and cancel buttons), direct manipulation (e.g. scroll bar sliders), form filling (e.g. Print dialogue box), and menus (e.g. Mac pull down menus)