Design Principles: 2. Mental models.

The main goal:design beacons the right model

  • User’s model develops through interaction with the system
  • Designers often expects user’s model to be the same as theirs
  • But often it isn’t!

People reason about new interfaces by analogy to old interfaces that they’re more familiar with. And when can leverage that — when you can figure out what people are familiar with — and use those metaphors intentionally in the construction of new interfaces, you’ll often be really successful.

The models that we build that guide our action: We have about our behaviour, of other people’s, of objects, of software — really anything and anybody that we interact with. But that’s not to say that everything is tidy and organized upstairs: Our mental models are incomplete; they’re inconsistent; they change over time; and they’re often rife with superstition.

Slips vs. Mistakes

With a slip, you have the right model of how a system works, but you just accidentally do the wrong thing. So, if I go to reach for one button and press another — just by a motor error — that would be a slip.

Slips you’ll most often try to prevent by improving the ergonomics or visual design of the user interface — spread things out so it’s less likely that you’ll hit the wrong thing; make targets bigger.

On the other hand, a mistake is when I do what I intend to do, but I have the wrong model of what I ought to do. So, if I’m driving, and I think that I ought to take this highway exit to get [to] where I need to go, and I take it exactly as I intend to, but I was wrong in my belief, that would be a mistake.

With mistakes, on the other hand, what you’ll need to do is [to] provide better feedback, or make clear what the options are.

Butterfly ballot, example of mistake
Electroic voting system — a solution for ballot case
Good example of UI: Mercedes S500 car seat controller

Direct manipulation enables users to behave with much more expertise by leveraging familiar real-world metaphors. This “directness in real-world” metaphor — like “to move a slider you move a slider” — helps give users a good idea of how each object works and how to control it. And also, the interface’s physical form discloses what functionality it provides.

Direct manipulation provides:

  • Leverages real-world metaphors
  • Good idea of how each object works and how to control it
  • Interface discloses how to use it

Jonathan Grudin points out, if technology is providing an advantage — if there is this new functionality — at some point, the correspondance to the real world has to break down. So this gap between the new technology and the current practice is necessarily going to be there. But your goal, as a designer, is to minimize this distance as much as possible.

Final Scratch system — a good example of real-word metaphor and innovation connection

When used well, physical interfaces that leverage people’s dexterity, manual abilities, and intuitions about the physical world can be incredibly powerful.

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