The Representation of how, a software program, mobile gadget or a UI works is called Implementation Model.
To use a gadget or a program, the user need not completely understand how the gadget works. Its way too complicated for the User to do the same. The User then creates a simpler cognitive short hand, which is good enough for him to perform his tasks and achieve his goals. This is called User Mental Model.
When a user plugs his mobile charger into any electrical plug point, he “associates” electricity flow to that of water flow. In reality, the “flow” is different.
While watching a movie, a user simply thinks that the projector is projecting light on to a screen. He is not really bothered about how many frames are projected per minute and how sound tracks are synched with video track etc.,
Mental models include what a person thinks is true, not necessarily what is actually true.
Mental models are similar in structure to the thing or concept they represent.
Mental models allow a person to predict the results of his actions.
Mental models are simpler than the thing or concept they represent. They include only enough information to allow accurate predictions.
Most software conforms to Implementation Model. However, a lot of Interface Designers follow what is called as “Represented Model”. This model displays UI more in terms of Mental Model of the user than in terms of Implementation Model.
While changing the “variations”(Image > Adjust > Variations) value in Adobe Photoshop, one will be able to see a real time preview of the image in multiple colors. This conforms more to the User’s Mental Model Vs the usage of values (0 to 100: implementation model)
Represented Models must shift more towards User’s Mental Model and away from Implementation Model