Chapter 6 Displays (13 Principles of Display Design (Perceptual…
13 Principles of Display Design
Make displays legible (or audible)
Integrates nearly all information in visual & auditory (contrast, visual angle, illumination, noise, masking, etc.)
Legible displays are necessary, although not sufficient.
Avoid absolute judgement limits
Do not require operator to judge level of a represented variable on a basis of ONE sensory variable (color / size / loudness) which contains more than 5 to 7 possible levels.
E.g. Using color-coded map with 9 hues invites errors for judgement.
People perceive and interpret signals according to what they expect to perceive based on past experience.
If signal is presented in contrary to expectation (warning / alarm), more physical evidence must be presented to guarantee correct interpretation.
Some expectencies are based on long term memory.
In degraded viewing or listening conditions, a message is more likely to be interpreted correctly when expressed more than once.
Particularly true when message is presented in other physical forms.
(e.g. tone + voice, voice + print, print + pictures, color + shape)
Using 2 or more forms, the degradation factor might only affect one of the forms.
Similarity causes confusion.
Similar signals are likely to be confused when perceived or after a delay when retained in working memory.
Designer should delete unnecessary similar features and highlight different ones to create distinctiveness.
Mental Model Principles
A display should look like the variable that it represents.
E.g. thermometer has a high and low value, therefore should be oriented vertically.
Displays with multiple elements should be configured in a manner that they would be configured in the environment.
Moving elements of displays of dynamic information should move in a spatial pattern compatible with users' mental model of how it moves in the physical system.
E.g. Element of altimeter of aircraft should move higher as pilot thinks that aircraft moves upward.
Principles Based on Attention
Minimizing information access cost
There is cost in time and effort to move selective attention from one display location to another to access information.
Good designs minimize net cost by keeping frequently-accessed sources in a location in which the cost of travelling between them is small.
E.g. keep displays small so that little scanning is required to access information, but it may reduce legibility
2 or more sources related to the same task must be mentally integrated to complete the task.
E.g. graph line related to its legend, Plant layout related to its warning indicator meanings.
Divided attention between two information sources for one task is necessary.
Complements principle 8 (put 2 sources close to reduce information access cost)
However, too much close proximity not always good. overlapping images make perception hard.
Principle of multiple resources
Processing a lot of information can be facilitated by dividing the information across visual / audio concurrently, rather than all information using one medium only.
Replace memory with visual information
People should not be required to SOLELY retain info in working memory / retrieve from long term memory.
E.g. experts may like retrieving information by direct commands, such as search box (knowledge in the head), rather than stepping through a menu (knowledge in the world)
Good design balances the two kinds of knowledge.
Prediction is difficult and cognitive task, heavy on working memory.
Displays that can explicitly predict what will happen are generally quite effective in supporting human performance.
Predictive display removes a resource-demanding cognitive task and replaces with a simpler perceptual one.
When long term memory works too well, it may continue to trigger actions no longer appropriate.
Good designers should accept and design displays that are consistent with other displays perceived previously.
E.g. Consistent color coding across a set of displays, so that red color always means the same thing.