INF385P – Software Usability Engineering

R. G. Bias | School of Information | SZB 562BB | Phone: 512 471 7046 | [email protected] 1

i

INF385P – Software Usability Engineering

Week 2 – Norman’s book and mental models


iI’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.


iChapter 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.


iGood 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.


iNatural 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?)


iMapping

• 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.


iGood 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:

http://www.asktog.com/basics/firstPrinciples.html


i“First Principles”

“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


iAffordance• 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.


iComplex 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.


iPrinciples of Design

• Four principles of Design for Understandability and Usability.

1. 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.


iPrinciples of Design (cont’d.)

2. Make things visible.3. 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.


iPrinciples of Design (cont’d.)

4. The principle of feedback.– Feedback is sending back to the user

information about what action actually has been done, what result has been accomplished.


iThe 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.


iChapter 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.


iModels• 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.


iModels (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.


iBlame• 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.


iExplanation

• 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.


i7 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:

1. Doing something (execution)

2. Checking (evaluation)


i7 Stages (cont’d.)

• Action is broken down into 7 stages:1. Perceiving the state of the world

2. Interpreting the perception

3. Evaluating the interpretations

4. Setting a goal

5. Intention to act

6. Sequence of actions

7. Execution of actions


i7 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.


iGulfs . . .

• 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.


iDesigning

• 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.


iDesigning (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!


iChapter 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.


iKnowledge• Precise behavior can emerge from

imprecise knowledge, because . . .1. Information is in the world (e.g., signs).

2. Great precision is not required. (Not just one path to school.)

3. Natural constraints are present. (Didn’t have to worry about going UP as you drove to school.)

4. Cultural constraints are present (e.g., driving on the right).


iBehavior

• 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.


iIn 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.


iKnowledge 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


iConstraints• 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.


iMemory

• . . . 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.)


iMemory 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


iMemory 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


i3 Categories of things remembered

• Memory for arbitrary things, meaningful relationships, memory through explanation

1. 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.


i3 Categories of things remembered (cont’d.)

2. Memory for meaningful relationships– Enabled by mental models– Interpretation is essential, but it is NOT

understanding.


i3 Categories of things remembered (cont’d.)

3. 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.


iMemory . . .

• . . . 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.)


iReminding• 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.


iIn the World

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


iNatural 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.


iTradeoff . . .

• . . . 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.


iCh. 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.


iDesign• 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.”


iConstraints - 4 Classes

• Physical

• Semantic

• Cultural

• Logical


iPhysical 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.)


iSemantic 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!


iCultural 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.”


iLogical Constraints

• Logic dictates that all parts be used, and fit together.

• Natural mappings work by providing logical constraints.


iThe 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.


iThe Problem with Switches• 2 fundamental problems

• Grouping problem (which switch goes with which function)– Controls that cause trouble should not be located

where they can be operated by accident.– Solution -- separate the switches for two sets of

functions – Another solution -- use different types of switches– Combine the two solutions


iThe Problem with Switches (cont’d.)

• Mapping Problem (which switch goes with which light)– Unsolvable given current light switch design

(mismatch in spatial arrangement (horiz. vs. vert.) makes a natural mapping impossible.

– Match the layout of the lights with the layout of the switches.


iVisibility and Feedback

• Visibility -- make relevant parts visible

• Feedback -- give each action an immediate and obvious effect


iUsing Sound for Visibility• Sounds should be generated to give info about the

source• Should convey something about the actions that are

taking place• Natural sounds (not beeps) reflect the complex

interaction of natural objects– The way one part moves against another– The material of which the parts are made -- hollow

or solid, metal or wood, soft or hard, rough or smooth

• One of the virtues of sounds is that they can be detected even when attention is applied elsewhere. But, thus, can be obtrusive.


iCh. 5 - To err is human

• Errors come in several forms– Slips -- result from automatic behavior,

when subconscious actions get waylaid en route (“performance errors”)

– Mistakes -- result from conscious deliberations (“competence errors”)


iIn terms of the 7 stages of action . . .

• If you form an appropriate goal, but mess up in the performance, you’ve made a slip.

• If you form a wrong goal, you’ve made a mistake.

• Slips are usually small things, relatively easy to discover.

• Mistakes can be more major, harder to detect. (Says Norman.)


iSlips

• Show up most often in skilled behavior. (Does that seem contradictory? Think about it.)

• We don’t make many when we are still learning.

• Result from lack of attention. (Or from a speed-accuracy tradeoff.)


iTypes of Slips• Capture errors -- a frequently done activity suddenly takes charge

instead of the intended one (e.g., typing THE instead of THY).• Description errors -- the intended action has much in common with

others possible (e.g., turn on the wrong burner on stove).• Data-driven errors -- automatic actions, triggered by the arrival of

some sensory data, intrude into an ongoing action sequence (e.g., pick up the phone when you hear a ring on TV).

• Associative activation errors -- internal thoughts and associations intrude, causing errors (e.g., think you’re leaving a phone message for your wife, end with “I love you”).

• Loss-of-activation errors -- simply forgetting to do something• Mode errors -- when devices have different modes of operation,

and the action appropriate for one mode has different meaning in another mode (e.g., hitting the accelerator pedal when in neutral).


iModes

• Modes can be detected only if there is feedback.

• Problem of level -- where (at what level in the sequence) is the error?

• Problems of level constantly thwart the correction of error.


iDesign

• Design lessons from the study of slips.– Don’t prevent errors by requiring

confirmation.– Rather, eliminate irreversible errors.


iMistakes

• Mistakes as errors of thought. (Competence errors.)

• Mistakes result from the choice of inappropriate goals.


iThree Models of Human

Cognition1. Photo Album Theory. (BUZZZ. Thank you for

playing.)

2. Schema Theory.– Filing cabinet model– Lots of cross-references and pointers– Basic beliefs

• There is logic and order to individual structures (schema)• Human memory is associative, with each schema pointing

and referring to multiple others (networked!)• Much of the power for deductive thought comes from using

the info in one schema to deduce the properties of another.


iThird Approach -- Connectionist

– Still unproven

– Less logical

– Each connectionist unit (whatever!) is connected to many others

– Signals are either positive (activation) or negative (inhibition)

– Thoughts = stable patterns of activity

– New thoughts are triggered by a change in the system (from within or without) -- new info arrives and changes the pattern of activation and inhibition

– Referred to as the “multiple exposure” theory of memory

– Good quote, p. 118, last para., through middle of p. 119.


iTasks

• The structure of tasks.

• Everyday structures are either shallow and wide (ice cream list) or narrow and deep (cookbook).

• Any task that involves a sequence of activities where the action to be taken at any point is determined by its place in the sequence is “narrow.”


iTasks (cont’d.)

• Most tasks of daily life are routine. Shallow or narrow.

• What are NOT everyday activities? Those with wide or deep structures, that require considerable conscious planning and thought, deliberate trial and error. (Did someone say surfing the web to find some particular info?)


iConscious and Subconscious Behavior

• Much human behavior is done subconsciously– without conscious awareness– not available to introspection

• Subconscious thought matches patterns– finding best match between past experience and

current needs– proceeds rapidly, automatically, without effort– good at generalizing– but can find inappropriate matches– a bias towards regularity and structure


iConscious Thought– Slow and labored– Ponder decisions, consider alternatives, compare

choices– Slow and serial– Limited by small STM– Uses subconscious thought as a tool– memory limitation is overcome by appropriate

organization structure• Mistakes are made by mismatch -- by taking current

situation and falsely matching it with something in the past.


iDesigning for Error• Everyone makes errors• Designers make the mistake of not taking errors into

account• Read p. 131 for list of what designers SHOULD do• Forcing functions -- form of physical constraint

– Can’t put convertible top up or down unless the car is in “park.”

• Read “A design philosophy,” p. 140.


iCh. 6 -- The Design Challenge

• Norman talks about what forces work against evolutionary, or natural design (pp. 142-143).– The demands of time (quick product cycles)– The pressure to be distinctive (related to the

curse of individuality)


iTypewriter - Case History

• Note the important design lesson on p. 150.

• To wit: Once a satisfactory product has been achieved, further changes may be counterproductive. – (What does that have to say about web site

design.)

• Norman says you have to know when to stop.


iPitfalls

• Three reasons why designers go astray:

1. Putting aesthetics first

2. Designers aren’t typical users

3. Designers’ clients may not be the users


iComplexity of the Design Process

• Not a lot of meat in this chapter

• Understand the concepts of – selective attention– the problem of focus

• Understand the “two deadly temptations for the designer”– creeping featurism– worshipping false images (e.g., complexity)


iFinally . . .

• . . . toward the end of the chapter (about p. 177) he starts getting into computer systems.

• That’s a pointer to our final projects.


iCh. 7 - UCD

• Chapter 7 is the “punch line” of the whole book.

• User-Centered Design

• Most of the chapter is given over to describing “seven principles for transforming difficult tasks into simple ones.”


iPrinciple 1

• Use both knowledge in the world and knowledge in the head.

• Here Norman refers to his distinction between the mental models of the designer and the user, and the relationship between these and the actual system.


iPrinciple 2• Simplify the structure of tasks• Here Norman recalls our discussion of STM and LTM,

and their different weaknesses. He also offers 4 “major technological approaches” that “can make the mappings more visible or, better, more natural.”– 1 Keep the task much the same, but provide mental

aids.– 2 Use technology to make visible what would otherwise

be invisible, thus providing feedback and the ability to keep control.

– 3 Automate, but keep the task much the same.– 4 Change the nature of the task.


i3, 4, 5

• Principle 3 -- Make things visible: Bridge the Gulfs of Execution and Evaluation.

• Principle 4 -- Get the mappings right.

• Principle 5 -- Exploit the power of constraints, both natural and artificial.


i6 and 7

• Principle 6 -- Design for error. Assume that any error than can be made will be made.

• Principle 7 -- When all else fails, standardize.


iEtc.

• He goes on to offer a section on why you might want to design something to be hard to use ON PURPOSE.

• And he ends with a few sections on writing, the home of the future, and a concluding section.


iNext . . . your homework

• Bad designs.• Good designs.

Famous quote: “No one ever raised a statue to a critic.” Sibelius

I want us all to remember that it is easier to criticize another design than it is to design something.


iNow . . .

• Let’s try to put it in Norman’s terms why the good designs were good and the bad designs were bad. (“Some important feature was, or was not, visible.”)


iNext week

• We’ll talk about perceptual and cognitive psychology – a little about what we know about how human beings take in and process information.

• Homework – good and bad WEB designs, to class next week.

• White paper due in five weeks. Don’t forget to have your topic OK’d by me.

• http://bbspot.com/News/2003/07/letter_c.html

Documents

INF385P – Software Usability Engineering