Information Representation Need to break representations into component forms, for analysis and for design Establish a common language for discussion Few frameworks available

Wood’s levels of Representation Workspace Views Graphic Forms Graphic Fragments The Graphic Atom

Workspace A coordinated set of view and the global relationships between them. Design decisions: salience of process views, organisation and arrangement of process views, positioning of viewports, size and background overall display issues, navigation

Prototype Hercules Display

Process Views Graphic Forms joined with a common context Design Issues are: salience and arrangement of graphic forms, organisation, grouping, backgrounds Valve 1 Valve 2

Graphic Forms A more meaningful unit shows changes and anomolies Design issues are how to convey context, and salience

Graphic Fragments Words, numbers, bars, scale, labels Design decisions: position, content of numbers, words, relation to near fragments, (proportion, salience) temperature

Graphic Atom Smallest unit a letter, digit, line, colour block Design decisions: colour, size, shape, length, thickness, angle, etc. A 3

Forms of Reference 3 kinds Propositional Iconic Analogical Describe how the visual token relates between the user and the world

Propositional Form Token tells the observer about the world Relation between the token and the world is arbitrary Typically words, numbers, some graphics Relies on stored knowledge such as language, numbers Gives current state but little more ObserverTokenWorld “tells” arbitrary

Iconic Reference Relies on observer experience with the world depends on quality of visual form to look like the world should evoke recognition typical “icons” ObserverTokenWorld recognizes looks like

Analogical Reference May or may not look like world Typically graphs on contextual backgrounds ObserverTokenWorld Processes constraint captures natural constraint

Examples Stop light propositional

Airline departure and arrival signs iconic

Stop Sign STOP propositional

Stove Labels “REAR” “FRONT” propositional iconic

Can you have too many icons? Early trend of using icons as “user-friendly” A good idea taken too far? Examples: Iconization of non-visual things (is that still iconic reference?) Poorly drawn or obscure icons Aiding with words an indicator

Mixed Forms of Reference Windows Recycle Bin –Recycle Biniconic –darkens/lightenspropositional –fills/emptiespropositional

Map Wordspropositional Symbolspropositional landmark imagesiconic spacing and scaleanalogical

Final Notes Propositional and Iconic usually give 1 piece of information Analogical usually gives many pieces Representation is not right or wrong but changes the work of the observer

Work involved in processing representations Analogicalperceptual Propositionalmemory Iconicrecognition memory (Propositional and Iconic both rely to some degree on knowledge in the head. Analogical leaves knowledge in the world.)

Graphic Forms Analog vs. Digital DIGITAL: –uses propositional reference –set of numerical strings that describe the referent e.g –observer reads the information

Digital Forms only current state is available very difficult to display history of the referent past or future states must be –remembered –calculated Memory and mental workload for user

Analog Uses analogical reference data is represented by a relationship between visual tokens on the screen representation is not as direct as digital requires the interpretation of a position in space

Analog Relationship is typically between an indicator and a reference scale Reference scale = Frame of reference.

Frames of Reference 1-dimensional frame of reference indicator scale 2-dimensional frame of reference scales indicator

Main Differences (A/D forms) 1. Generality vs. Precision –digital is precise and explicit –analog is more general, harder to extract precise values 2. Parallel vs. Serial Display –digital tells you 1 piece of data (serial) –analog permits parallel data display and integration with other data

Main Differences (A/D forms) 3. Context –analog shows current value against the complete set of values that the referent can take –digital just shows the current value Max value Min value Current value Distance to max value Distance to min value

In terms of Workload Analog is generally easier because it is processed perceptually Digital requires mental comparisons and memory The Principle of the Primacy of Perception: Whenever you can offload a mental task to a perceptual task you take advantage of human capabilities and make work easier.

Using Digital Forms Digital Forms typically consist of two parts –1. An identifier or label tells you what the referent is –2. A dynamic description of the referent the value The visual form is typically a string of alphanumeric characters but could be icons.

Design Issues with Digital Forms 1. Precision –how much precision (# of significant digits) should you have – vs. 100

Design Issues with Digital Forms 2. Context –how will you show context? When the referent hits its max value? When the referent hits its min value? On/off a desired value? –People often change colour (propositional ref)

Design Issues with Digital Forms 3. How will you handle change and rate of change information? Change over time? Direction of change? 4. Digital is best choice when precise reading is required 5. Digital makes the most efficient use of screen space. 6. Digital forms are overused.

Showing Context with Digital Forms Change the colour of the numbers for meaning e.g. red for alarms Arrows to show rate and direction of change Ratios to show performance relative to a target value C Units also add context.

Design Issues with Analog Forms 1. You need to show all the values that the referent could take –maximum –minimum –offscale –failed sensor

Design Issues with Analog Forms 2. Put the value in the context of reference values 3. Design multiple elements –indicator –scale –labels

Possible Reference Values 1. Value vs. its past values –changes over time, rate of change 2. Value vs. its future values –predicted values 3. Value vs its target value (or range) –setpoints

Possible Reference Values 4. Value vs. its alarm limits –is it approaching a dangerous value? 5. Value vs. its max/min values 6. Value vs. decision points that affect operation. –Eg. Automatic system activations.

Graphical Techniques “Trend plot” –plot variable against time –gives current value (x), history, rate of change (dx/dt), rate of rate of change (d2x/dt2) x time

Graphical Techniques “Trend plot” –shade regions to show target values or alarm limits x time Alarm region Target region

Graphical Techniques “Trend plot” –“marker bars” on the scale –improved salience by adding indicator x time Alarm region Target region

Hercules display Mostly analog forms Polar star - several scales put together Trends - used a combination of analog and digital forms to get context and precision.

Polar Star Display scale Current value High limit Low limit

Other Analog Forms Combined with digital

Stacked Bar Graphs - multiple analog forms v1 v2 v3 v4 Height=v1+v2+v3+v4

“Icons” that are Analog Icon “fills” with water to show level

More analog forms Degree of rotation shows degree valve is open.

Air Traffic Control Display

Design Exercise You have been hired as an interface designer to work for Mrs. Field’s cookies. Mrs. Fields needs to know when the oven isn’t working correctly. Sometimes it overheats and sometimes the burners break and don’t come on. Sometimes it heats up too slowly and the first few batches of cookies are ruined, being either burned or not baked through. Mrs. Fields wants to monitor her oven performance so that she can replace the burners before they break by knowing when they are not heating up properly anymore. In general, the oven thermometer has a range of 0 to 500 degrees F. Because of the different kinds of cookies, the oven is set to a new temperature with each new batch. Mrs. Fields needs to set her oven temperature to within 25 degrees. The cookie temperature can only range 25 degrees higher or lower from the setpoint temperature before the cookies are ruined. Design a display for the cookie oven. Identify the appropriate frame of reference, boundary conditions, reference values, and make decisions about what events to highlight.

Topics Summary Cognitive Ergonomics –Salience –Alarms Memory & Attention Display Representations –Information Representation (decomposition) –Forms of Reference (propositional, iconic, analogical) –Analog vs. digital