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INF385P – Software Usability Engineering

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  1. INF385P – Software Usability Engineering Week 2 – Norman’s book and mental models

  2. I’m gonna go fast because . . . • It ain’t rocket science. • You’ve already read the book. • I’d rather make you scramble to keep up than bore you. • I have 80 slides I’m gonna do in 60 minutes (yeah, right!). • While I’m presenting this, see if you can characterize your good and bad designs that you’ve discovered this week in Norman’s terms.

  3. Chapter 1 • The PsychoPATHOLOGY of everyday things • Assumption: We blame ourselves for errors, but the real culprit is faulty design. • Assumption: There’s nothing special about computers. They have the same sorts of design problems as simpler, everyday things.

  4. Good Design • Well designed objects . . . • are easy for the mind to understand • contain visible cues to their operation • Poorly designed objects . . . • provide no clues, or • provide false clues.

  5. Natural Signals • Natural signals lead to natural design. • A metal plate “naturally” is to be pushed. • Visible hinges “naturally” indicate attachment, and that the other side swings open. (And swings open TOWARD me?)

  6. Mapping • Mapping is a relationship between two things (e.g., between what you want to do and what appears possible). • Good design allows for a clear (visible) mapping between . . . • intended actions and • actual operations. • Now -- think of what this might mean in a web site.

  7. Good Design • Principles of good design • the importance of visibility • appropriate clues • feedback of ones actions. • Just so you’ll know -- others have proposed OTHER principles of good design. Go check out the web site of Bruce Tognazzini:

  8. “The following principles are fundamental to the design and implementation of effective interfaces, whether for traditional GUI environments or the web.” Anticipation Autonomy Color Blindness Consistency Defaults Efficiency of the user Explorable Interfaces Fitts’s Law Human-Interface Objects Latency Reduction Learnability Metaphors, Use of Protect Users’ Work Readability Track State Visible Interfaces “First Principles”

  9. Affordance • Affordance is the perceived and actual properties of a thing. • Primarily those fundamental properties that determine how a thing could possibly be used. • “Affords” means, basically, “is for.” • A chair affords support, therefore affords sitting. • Affordances provide strong clues to things’ operations. • When affordances are taken advantage of, the user knows what to do just by looking. • No label, picture, or instruction (“Push”) is required. • - When simple things need pictures, labels, or instructions, the design has failed.

  10. Complex World • 30,000 readily discriminable objects. How do we deal with all of them? • Partly, the way the mind works. • Partly, the information available from the appearance of objects. • Partly, the ability of the designer to: • make the operation clear, • project a good image of the operation, and • take advantage of the other things people might know. • Here is where the designer’s knowledge of the psychology of people coupled with the knowledge of how things work becomes crucial.

  11. Principles of Design • Four principles of Design for Understandability and Usability. • Provide a good conceptual model. • A good conceptual model allows us to predict the effects of our actions. • Simply knowing the relationship between the controls and the outcomes.

  12. Principles of Design (cont’d.) • Make things visible. • The principle of mapping. • Natural mapping (taking advantage of physical analogies and cultural standards) leads to immediate understanding. • Move the control up, the sound gets louder. • Seat adjustment in Fig. 1.13 is a good example.

  13. Principles of Design (cont’d.) • The principle of feedback. • Feedback is sending back to the user information about what action actually has been done, what result has been accomplished.

  14. The Paradox of Technology • Added functionality generally comes along at the price of added complexity. • The same technology that simplifies life by providing more functions also complicates life by making the device harder to learn and use. • The Paradox of Technology should never be used as an excuse for poor design. • Added complexity cannot be avoided when functions are added, but with clever design they can be minimized.

  15. Chapter 2 -- Psy of Everyday Actions • Norman’s credo on errors -- if an error is possible, someone will make it. • The designer must design so as to: • minimize the chance of errors in the first place • minimize the effects of an error • make errors easy to detect • make errors reversible, if possible.

  16. Models • Mental Models = our conceptual models of the way . . . • objects work • events take place • people behave • Mental models result from our tendency to form explanation of things. • Models are essential in helping us . . . • understand our experiences • predict the outcomes of our actions • handle unexpected occurrences.

  17. Models (cont’d.) • We base our models on whatever knowledge we have: • real or imaginary • naïve or sophisticated • even fragmentary evidence. • Everyone forms theories (mental models) to explain what they have observed. • In the absence of feedback to the contrary, people are free to let their imaginations run free. • More on models in Chapter 3.

  18. Blame • People assign causal relation whenever two things occur in succession. • When we try something and fail, we blame ourselves (especially when we know others have succeeded). • Thus, a “Conspiracy of Silence,” leading to • guilt • helplessness • Learned Helplessness • Taught Helplessness • Badly designed objects constructed so as to lead to misunderstanding (faulty mental models). Think of an internally inconsistent app or web site.

  19. Explanation • The nature of human thought and explanation. • We want to have an explanation, and we will construct one in order to eliminate any puzzle or discrepancy in our lives.

  20. 7 Stages of Action • On p. 47 is a series of four figures that illustrate Norman’s view of the structure of action. • Actions have two major aspects: • Doing something (execution) • Checking (evaluation)

  21. 7 Stages (cont’d.) • Action is broken down into 7 stages: • Perceiving the state of the world • Interpreting the perception • Evaluating the interpretations • Setting a goal • Intention to act • Sequence of actions • Execution of actions

  22. 7 Stages (cont’d.) • Specific actions bridge the gap between • What we would like to do (goals and intentions) and • All possible physical actions. • 7 stages form an “approximate model,” not a complete psychological theory. • One key -- continual feedback loop. • Process can be started at any point.

  23. Gulfs . . . • Of Execution and Evaluation. • Gulf of Execution -- the difference between intentions and allowable actions. • Gulf of Evaluation -- difficulty in interpreting the physical state of a “system,” interpreting how well the expectations and intentions have been met.

  24. Designing • The 7-stage structure can be a valuable design aid. • Provides basic checklist of questions to ask to ensure that • the Gulf of Execution and • the Gulf of Evaluation are bridged.

  25. Designing (cont’d.) • There’s a question to ask for each stage (see Fig. 2.7) and they boil down to the principles of good design: • visibility • good conceptual model • good mappings • feedback. • Next time you can’t immediately figure out the shower control in a motel, remember that the problem is in the design!

  26. Chapter 3 - Knowledge in the Head and in the World • Not all knowledge required for precise behavior must be in the head. It can be distributed: • partly in the head • partly in the world • partly in the constraints of the world.

  27. Knowledge • Precise behavior can emerge from imprecise knowledge, because . . . • Information is in the world (e.g., signs). • Great precision is not required. (Not just one path to school.) • Natural constraints are present. (Didn’t have to worry about going UP as you drove to school.) • Cultural constraints are present (e.g., driving on the right).

  28. Behavior • In everyday situations, behavior is determined by the combination of . . . • internal knowledge • external info • constraints. • There’s a tradeoff between the amount of mental knowledge and the amount of external knowledge needed.

  29. In the world • An example. • Typing: • Letter names on keycaps. • Requires that the typist look at keycaps. • Goal of power typing is to get that knowledge from the world into the head of the typist.

  30. Knowledge OF and Knowledge HOW • Knowledge OF = Declarative Knowledge • Knowledge of facts and rules • Easy to write down, teach • Knowledge HOW = Procedural Know. • Difficult or impossible to write down, teach • Best taught by demonstration and learned through practice • Largely subconscious

  31. Constraints • The power of constraints -- the “memory” for epic poetry is found to be mostly reconstruction, with the aid of the constraints of rhyme, meter, etc. • We use constraints to simplify what we must remember. • For example, putting mechanical parts together. • Some are constrained by what will and will not fit together. • Also cultural constraints -- screws tighten clockwise.

  32. Memory • . . . Is knowledge in the head. • Think of all you can remember. Phone numbers, postal codes, passwords, SSN, birthdays, etc., etc. • It’s tough! • So, we put memory in the world. (Daytimers. Palm Pilots. Address books. Stickies.)

  33. Memory Structure • Two major classes of memory: STM & LTM • STM • Memory of the just-present • Retained automatically • Retrieved without effort • Limited capacity (7 +/- 2) • Items easily bumped • Capacity can be increased by chunking • Items retained by rehearsal

  34. Memory Structure (cont’d.) • LTM • Memory for the past • Storage and retrieval takes time • Items stored according to interpretation (multi-keyed indexing) • Virtually unlimited capacity • Storage and retrieval are easier when the material makes sense

  35. 3 Categories of things remembered • Memory for arbitrary things, meaningful relationships, memory through explanation • For arbitrary things: • Rote learning • Takes more time to encode • When there’s a problem, memorized sequence of events gives no hint of what’s gone wrong or how to fix it. • We impose structure or associations to help • E.g., tune to help remember the alphabet • Items aren’t understood. No mental model.

  36. 3 Categories of things remembered (cont’d.) • Memory for meaningful relationships • Enabled by mental models • Interpretation is essential, but it is NOT understanding.

  37. 3 Categories of things remembered (cont’d.) • Memory through explanation. • Most powerful form of internal memory • Mental models play a major role -- simplify learning because the details can be DERIVED when needed. • NOTE: The use of mental models to DERIVE behavior is not ideal for tasks that must be done rapidly or smoothly. • Designers should provide users with appropriate models, ‘cause people make ‘em up, otherwise. • The power of mental models -- let you figure out what would happen in novel situations.

  38. Memory . . . • . . . is also knowledge in the world. • But only available when you are there. (What if you don’t see that note you left for yourself.)

  39. Reminding • A good example of the interplay between info in the world and in your head. • Strategies for reminding: • Rehearsal • Notes to self • Put the burden on the thing to be remembered (put the book by the door) • Two different aspects of a reminder • The signal (string around finger) • The message (ring around finger) • The ideal reminder has both components.

  40. In the World • Lots of products make it easier to put knowledge in the world. • Alarm clocks • Diaries • Calendars • Watches • PDAs

  41. Natural Mappings . . . • . . . Reduce the need for information in memory. • Simple design principle: • If a design depends on labels, it may be faulty. • Labels are important, and often necessary. • But the appropriate use of natural mappings can minimize their need. (E.g., stove controls.) • Wherever labels seem necessary, consider another design.

  42. Tradeoff . . . • . . . between info in the world and in the head. • Knowledge in the world acts as its own reminder. • Knowledge in the head is efficient. (You can travel light.) • Knowledge in the world is easier (no learn time), but often difficult to use. Relies heavily on the physical presence of info. • See Fig. 3.6, p. 79.

  43. Ch. 4 -- Knowing what to do • When we encounter a novel object, either • We’ve dealt with something similar before, and we transfer old knowledge, or • We get instruction. • Thus, information in the head.

  44. Design • How can the design of an object (NOTE: info in the world) signal the appropriate actions? • Natural (physical) constraints • Affordances, that convey messages about the item’s possible uses, actions, and functions • “The thoughtful uses of affordances and constraints together in design lets a user determine readily the proper course of action even in a novel situation.”

  45. Constraints - 4 Classes • Physical • Semantic • Cultural • Logical

  46. Physical Constraints • Constrain possible operations • Rely on properties of the physical world, so no special training is required. • Are made more effective and useful if they are easy to see and interpret. (Example: Glass over fire alarm.)

  47. Semantic Constraints • Rely on the meaning of the situation to control the set of possible actions. • Rely on our knowledge of the situation and the world. Example -- Windshield goes in front of rider, in Legos!

  48. Cultural Constraints • Signs are meant to be read. • Guidelines for cultural behavior are represented in the mind by schemas. • Schemas are “knowledge structures that contain the general rules and info necessary for interpreting situations and for guiding behavior.”

  49. Logical Constraints • Logic dictates that all parts be used, and fit together. • Natural mappings work by providing logical constraints.

  50. The Problem with Doors • An example of applying affordances and constraints to everyday objects. • When we approach a door we expect to find some visible signal. • Tells us where to act • Next step is to figure out how to act • Sometimes we need a manual (a one-word manual) • The proper hardware will operate a door smoothly PLUS will indicate how the door is to be operated • It will exhibit proper AFFORDANCES. • Focus on aesthetics can blind the designer (and the purchaser) to the lack of usability.