2. Good Design Visibility is key to interaction design Take advantage of affordances/constraints Provide a good conceptual model for the user

3. Mental models People form mental models of things they interact with Design model User’s model Designer User System image System

4. Mental models People form mental models of things they interact with When the number of possible actions exceeds the number of controls, there will be difficulty Added functions mean added difficulty

5. Mental models People form mental models of things they interact with When the number of possible actions exceeds the number of controls, there will be difficulty Added functions mean added difficulty QUICK! How do you take a screenshot on an iPhone?

6. Natural mappings

7. Seven stages of action 1.Forming the goal 2.Forming the intention 3.Specifying an action 4.Executing the action 5.Perceiving the state of the world 6.Interpreting the state of the world 7.Evaluating the outcome ExecutionEvaluation

8. Errors Everyone makes mistakes – designers make the mistake of not taking errors into account

9. Errors Types of error: 1.Mistakes: when you form the wrong goal 2.Slips: when you form an appropriate goal but mess up the performance – Types of slips: capture errors, description errors, data-driven errors, associative activation errors, loss-of- activation errors, mode errors

10. Errors Why we make mistakes: Human thought is based on past experiences Decision trees: width + depth = difficulty – Ice-cream menu = wide and shallow – Cookbook recipe = deep and narrow – Chess = oh God oh God oh God oh God oh God (Width and depth are often found in games)

11. Errors Designers should make errors as cost-free as possible Errors should be easy to detect, have minimal consequences, and be reversible

13. Psychology We have two kinds of knowledge 1.Knowledge of (declarative): Facts and rules, easy to write and teach 2.Knowledge how (procedural): Best learned by practice

14. We have three different types of memory 1.For arbitrary info 2.For meaningful relationships 3.For memory through explanation Rule of thumb If a design depends upon labels, it may be faulty.

15. Precise behaviour can emerge from imprecise knowledge if: The necessary information is in the world Precision is not required Natural constraints are in effect Cultural constraints are in effect Knowledge in the head can be more efficient, but it requires learning, which can be hard 

16. Constraints There are four classes of constraints: 1.Physical 2.Semantic 3.Cultural 4.Logical

17. Questions that guide our interactions: Which parts move? What part is to be manipulated? What movement is possible? What are the relevant physical characteristics of the movement? (How hard, how far...) What parts are supporting surfaces? How much size and weight will it support?

18. Problems of design Once it works, refinement may be counterproductive Users are often experts at the task, designers are experts at the device There is no such thing as the average person – design for flexibility/adjustability Account for handicaps, old age, physique, etc.

19. Problems of design Don’t focus on either satefy, usability, aesthetics, or manufacturability to the exclusion of the others Avoid feature creep by cutting features or by organising and modularising them Don’t worship false idols complexity

20. Explorable systems 1.User must readily see and be able to do the allowable actions in each system state 2.The effect of each action must be both visible and easy to interpret 3.Actions should be without cost

21. Computer systems Two modes of computer usage: – Third person: issue commands – First person: direct manipulation Make the computer system invisible

22. Left-over points Simplifying the structure of tasks: 1.Provide mental aids 2.Use technology to make visible what would be invisible, improving feedback 3.Automate but keep tasks the same 4.Change the nature of the task When automating, don’t take away control Some things should be difficult Difficulty and challenge ≠ frustration and error