“Many tasks involve the processing of information from different sources. Some information needed resides in the memory of the person. Other information is in physical things: dials, screens even the position of objects. Physical (and similarly virtual) objects act as memory aids. Is that all they do?”
“Physical objects do not just act as memory aids. They allow information to be directly perceived without any explicit interpretation being applied. They physically afford or prohibit behaviours and they change the very nature of the task for the user. Noughts and Crosses is not just easier because the square provides memory cues, it is easier because the cognitive processes involved in spotting winning sets has been changed, for example to ones involving direct perception based on location. Take the representational effect into account when designing interfaces and you can actively simplify a task.” (courtesy of InfoDesign)
Read: Paul’s Interactions: Spit-Not-So, or What’s in the Layout?