Human Factors Psychology #1

failure occurs at execution ex. taking wrong medication

error in planning ex. substituting butter for vegetable oil

intended action forgotten and not carried out ex. forget attachment in email

purposely ignore rule or procedure ex. ignore hand-washing at job

Mode Error
action is appropriate in one system mode, but is carried out in a different mode ex. forgetting to put car in drive after reverse

The study of designing equipment and devices that fit the human body, its movements, and its cognitive abilities.

Error of Commission
perform inappropriate action ex. timing, sequence, selection

Human Factors
The science of understanding the properties of human capability and applying this understanding to the design, development, and deployment of systems and services.

What is a human factor
A human factor is a physical or cognitive property of an individual that influences functioning of technological systems as well as human-environment equilibriums.

Error of Omission
fail to perform action

Input Error
information from the sensory and perceptual processes

Output Error
due to the selection and execution of physical responses

Mediation Error
cognitive processes that translate between perception and action

Recoverable Failure
can be corrected and consequences minimized

Non-Recoverable Failure
system failure is inevitable

Economic Ergonomics
By preventing health problems such as work-related musculoskeletal disorders, ergonomists not only improve well-being but reduce costs to companies and individuals

Can also improve quality of products

Successful HFE
Enhances performance
Reduce error
Increase productivity

Increases safety

Improves user satisfaction

Difficulty for human factors design:
Systems should be designed in a way that they are suited to every user…

If the system (simple or complex) does not work the way a person thinks it should work then the person will be unsuccessful when attempting to use the system

Relationship between the properties of a physical object and the capabilities of the human that determine how the object could possible be used

Solutions to the difficultys of human factors
System design
Task design
Environmental design

Foundations of Science
Based on empiricism:
Knowledge by observation

Continually test scientific statements with observations
Revise scientific statements

Systematically apply the scientific method

Scientific Method
Logical approach to obtaining answers to questions
Often equated with hypothesis generating and testing

1.Goals of Science.
2. How is it obtained?
2.This is achieved by collecting data (gathering facts) to build a theory
The theory provides the best explanation for the findings in the research

Four Benefits of theory
1.Enables sensible interpolation to a specific real-world problem when there are no data

2.Provides quantitative predictions of the type demanded by engineers and designers

3.Allows the practitioner to recognize relations between problems that seem unrelated on the surface

4.Can be used cheaply and effectively to aid system design

How do we understand the problem and how do we know what to measure?
1.Defines a domain of interest
-In HFE, this is usually human performance within a system
2.Defines the conditions under which we can make useful measurements
-If we are interested in the effects of cell phone use while driving, then we need to see people using cell phones while driving

1.What is an operational definition of a variable?
2.Why define them this way?
1.A definition of the variable in terms of the operations or techniques the researcher uses in order to measure or manipulate it
2.Forces us to describe abstract concepts in concrete terms

Independent variables
The variables that are manipulated or chosen by the researcher

Dependent variables
The variables that are measured by the researcher (in other words, the variables you want to know). They “depend” on the independent variable because you set up your experiment with the prediction that the dependent variable(s) will change based on the independent variable(s)

Human characteristics AKA individual differences

The consistency of measurements

Any measure has 2 parts:
True effects
Random error

Operating Error
a system is not used according to correct procedure

anything which
– Is not an inherent characteristic of the human/machine system
– Is not inherent in the information to be processed
– Is (usually) expected to degrade system performance

general energy level of the operator (more stress –> more arousal)

Yerkes-Dodson Law
Yerkes-Dodson Law

Psychological Stressors
anxiety, frustration, fatigue, fear of failure, threat, incentive

Environmental Stressors
noise, temperature, vibration etc.

Design Error
system designer creates an error-likely situation by failing to consider human tendencies or limitations

Stress on arousal/alertness
– increase attentional selectivity
– under low stress, attention can be too non-selective
– under high stress, attention can be too narrow

Stress on working memory
– complex tasks rely more on working memory

Stress on decision making
– less deliberative, more intuitive/fast
– more OR less risk averse

– a tendency to repeat the response to an experience in later situations where it is not appropriate
– increased by stress

Reduce negative effects of stress
– strategies to cope with stressors
– minimize working memory demands

Hindsight bias
errors look obvious in retrospect

Stress on speed and accuracy
Under high stress people are more likely to emphasize speed at the expense of accuracy

The Goal of human factors
Use knowledge about human cognitive, physical, and social characteristics to design machines, tools, and systems that are easy and safe to use

Stress and Performance
For best performance, the optimal level of arousal depends on task complexity (high arousal on simple task, low arousal on difficult tasks)

Data-Limited Processing
The information input to a stage is degraded or imperfect ex. visual stimulus only briefly flashed

Resource-Limited Processing
The system is not powerful enough to perform the operations required for a task efficiently ex. system used to remember phone number before dialing

Perceptual Stage
what is perceived by sensory organs, depends on quality of input

Model of Working Memory
Model of Working Memory
phonological loop: articulatory loop and acoustic store

Working Memory
Second in cognitive stage: from attended sensory memory
– maintained with rehearsal
– unrehearsed information is quickly lost
– can retrieve from long-term
– phonological loop (sound of language)
– Visuo-spatial sketchpad (visual and spatial info)

Cognitive Stage
classifies stimulus, may include: retrieval of information from memory, comparison of displayed items, comparison of items and memory, arithmetic operations, and decision-making

Sensory Memory
first in cognitive stage: from sensory input
– unattended information is lost
iconic: visual
echoic: auditory
haptic: touch

Long-Term Memory
third in cognitive stage: from encoded working memory
– some info lost over time

Action Stage
overt response is selected, programmed through neuromuscular commands, and executed

Why is human factors important?
Daily occurrences such as accidents at work, in traffic, and at home, as well as disasters involving cranes, airplanes, and nuclear power stations can often be attributed to human error

Analysis of these failures shows the cause is often a poor and misunderstood relationship between operators and their task

Three Stage Model
Stimulus -> Perception -> Cognition -> Action -> Response

Human Information Processing
human as a communication system that receives input from the environment, acts on that input, and then outputs a response back to the environment

Structurally Limited Processing
Inability of one system to perform several operations at once ex. two competing movements performed simultaneously with the same limb

the absolute limits of the sensory systems to provide information that a stimulus is present

the ability to determine that two stimuli differ from each other

Psychophysical Scaling
discovering the relation between perceived magnitude and physical magnitude

Absolute threshold
Smallest amount of intensity needed for a person to notice a stimulus, Developed by Fechner

The degree to which an experiment, a procedure, or a measurement represents what it is supposed to represent

Construct validity
does the measure that is employed actually measure the construct it is intended to measure?

Internal validity
can the relations observed can be attributed with a high degree of confidence to the variables of interest? i.e., the ability to draw conclusions about causal relationships from our data.

Classical Methods
absolute and difference thresholds
pros: learn what is within range of perception
cons: measures are subjective and vary between people, response bias

Signal Detection
Observer is required to discriminate trials on which the stimulus is present from trials on which it is not
yes response and signal = hit
yes response and noise = false alarm
no response and signal = miss
no response and noise = correct rejection

Direct Scaling Procedure
Ask the perceiver to rate the perceived intensity of the stimuli

Indirect Scaling Procedure
Derive the quantitative scale indirectly from a perceiver’s performance at discriminating stimuli, i.e. choosing which is louder

descriptive research method cont:Naturalistic observations and ethnographic methods
-Great ecological validity
-Used to characterize how people interact with a system in the “real world”
-Measurement issues:
Observations can be recorded at the time they are made or later
Content and amount of detail in observations vary
Length of time during which observations are made can be short or long
Observations can vary in terms of the amount of inference, or degree of interpretation, that is required to classify events into measurement categories

descriptive research cont:Surveys and Questionnaires
-The best way to begin addressing a problem by asking people in the natural environment
-Steps to a good survey/questionnaire
1.Decide on the information you want the questionnaire to provide
2.Decide what type of questionnaire should be used
If you decide to write your own questionnaire, the third 3.step is to write a first draft
4.Revise questionnaire
5.Pretest the questionnaire
6.Finalize the questionnaire

Simple reaction time (SRT)
fastest, single response is made after the action occurs ex. press button when you hear sound

descriptive research cont:Interviews and Focus Groups
-Structured and unstructured interviews with users at any phase of the research process and for a variety of purposes
-Do not work well for discovering specific usability problems in a system

Descriptive research cont….again: Correlational and Differential Research
-Must decide ahead of time which behavioral variables we will measure
-Measure the degree of relationship between the variables
-This can be used with any data obtained from Descriptive Methods
-Valuable because they enable prediction based on the previously observed relationships

Correlational research
measure the strength of a relationship between two or more variables

Experimental research
-Test a hypothesis that makes a causal statement about the relation among variables
-Compare a dependent measure at at least two levels of an independent variable
-Randomly assign people to experimental conditions to make sure that the effects of many potentially confounding factors are distributed equally across conditions

Recognition reaction time (RRT)
single response is made after some stimuli (the “memory set”), but not after others (the “distractor set”) i.e. only press button for high pitch, not low pitch

Choice reaction time (CRT)
more than one response can be made and the correct response depends on the stimulus that occurs i.e. press left arrow key for left, right arrow key for right

Stevens' Law
Stevens’ Law
The relationship between physical intensity and psychological magnitude (perceived magnitude)

S = aI^n

S reported sensory experience
a constant
I physical intensity
n exponent that varies between senses

Reaction Time
amount of time between event and person’s response

Differential research
observe two or more groups that are differentiated on the basis of some preexisting variable

types of research methods:
2.Correlational and Differential

Descriptive research method
When you want to examine a situation that cannot be replicated
You are unable to exercise any control over the events under the investigation
Control can lead to a loss of ecological and external validity
Using sources like Archival Data to obtain information about a system
Archival data is data obtained from preexisting data collections like the census

External validity
can the results or the principles derived from the results can be generalized to a variety of other settings?

Ecological validity
do the behaviors observed in the study reflect the behaviors that actually occur in a natural setting?

Method of Limits
different stimuli intensities in sequential order

Difference threshold
Smallest amount of difference needed for a person to perceive two stimuli as different, Developed by Fechner

Method of Constant Stimuli
different stimuli intensities in random order

Color Perception
determined by wavelength (and other psychological factors), white/purple largest and red smallest

Within Subjects experiments
-Use the same participants in each condition
-Increases sensitivity of the design (more likely to find significant effects)
-Reduces the number of participants needed
-Major drawbacks:
Carryover effect: previously received treatment conditions influence a subject’s performance on subsequent conditions
Practice/Fatigue effects: increase/decrease in performance due to experience

Spectral Colors
comprised of single wavelength: ROYGBIV

Non-Spectral Colors
color comprised of more than one wavelength

Whenever possible, use experimental designs
Optimizes internal validity
With the right setting, can be excellent external validity

Descriptive methods can provide info about real-world systems that cannot be obtained from controlled experiments
Good for obtaining quick info about user characteristics and usability

– how easy is it to learn?

Design involves:
Designing new products
Modifying existing products
Designing environments
Develop training programs or instruction manuals
Organizational development and restructuring

Physically measured in Luminosity, perceived as “brightness”

how quickly and accurately can you do it?

how easy is it to remember?

increase the user’s satisfaction with the system

Low Error Rate
reduce the number of possible errors

Defined 7 principles for transforming difficult tasks into simple ones (aka achieving usability):
1.Knowledge in the World + Head
2.Simplify the Structure of Tasks
3.Make Things Visible
4.Get the Mapping Right
5.Exploit the Power of Constraints
6.Design for Error

Knowledge in the World
Sources of information outside of the individual
Ex. Maps, signposts, labels, recipes, speedometer in a car

Knowledge in the Head
Information from the world that has been internalized
Ex. Affordances

Make things visible: Gulf of execution & evaluation
Gulf of Execution:
The gap between the user’s goal of action and the means to execute that goal

Gulf of Evaluation:
The degree to which the system provides representations that can be directly perceived and interpreted in terms of the expectations and intentions of the user


Get the Mapping Right- Make sure that the user can determine the relationships:
Between intentions and possible actions
Between actions and the effects on the system
Between actual system state and what is perceivable by sight, sound, or feel
Between the perceived system state and the needs, intentions, and expectations of the user

Described as “Response Compatibility”-
Movement of control should match outcome goal
When you turn the steering wheel left, the car should turn left

Simplify the Structure of Tasks
-Provide simple mental aids
Ex. Warning labels
-Manage visible information
Ex. Provide speedometers to drivers
-Change the nature of the task
Ex. Cashiers scan barcodes instead of typing in numbers
-Making a task too simple can cause the user to lose some control of the system
Ex. Preprogrammed radio buttons inhibit finding new stations

Make Things Visible: Feedback
When a user interacts with a system, the system should provide information that the interaction was successful or an error was made

When you can’t exploit the previous principles… make everything the same
Creates Knowledge in the Head
Ex. Driving on the right side of the road
Without conforming to standards, you can confuse people which causes errors
Ex. Walking on the left side of a two-way door

Exploit the Power of Constraints
Constraints can be used to prevent error:
-Only one option

-Forcing function

Design for Error
People will make errors
Make it easy to recover from them!
Design around them when possible

When Difficulty is Good
Sometimes we want things to be difficult
Ex. Fences block dangerous areas
Ex. Child-proofing medications

Use the same principles.. only opposite

Evaluating:Front End Analysis
Before any design solutions are generated, answer the following:

Who are the system users?

What are the major functions of the system?

What are the environmental conditions?

What are user preferences and requirements?

Evaluating:User Analysis
Who are your users?
-Characteristics of users
-Include all types of current users
-Anticipate for potential users

Develop personas
-Hypothetical person derived from real user statistics

Evaluating:Function Analysis
What functions should be performed by the system?
Functions represent a general goal, not the actual tasks

Function: Record a TV show
Tasks: Turn on the TV and cable box, select the channel to record, select the time period to record, set recording settings

Evaluating:Task Analysis
What are the specific activities performed by the human when interacting with the system?
Should include:
-Functions of system
-More specific tasks to be performed
-Concurrent activities

Complexity will vary

Evaluating:Task Analysis cont.
Define the Purpose
-How will the data be used?
-How are processes related? (e.g., Information flow, Task sequence)
-What type of data should we collect?

Collect Task Data
-Under what conditions will this be performed?
-Collection methods: observation, think-aloud, task performance with questions, interviews, and focus groups

Summarize Data
-Identify the task process by using an outline, flow chart, timeline, or map

Analyze Data
-Determine the quality of a task by conducting a workload analysis, simulation and modeling, safety/hazard analysis, or scenario specification

Evaluating:Environment Analysis
Where will the tasks be completed and under what conditions?

Evaluating:User Preferences & Requirements
When different design options are available, you should determine the preferences and requirements of the intended users to guide design
Examples include:

Methods of collecting user preferences may include focus groups, questionnaires, etc

Final Test and Evaluation
Based on what you found…
Repeat the process in a more directed manner
Reach an evaluation decision

Heuristic Evaluation
Judge the compliance with HFE principles
-should be done by several people to compare results
-Not very scientific
-Good to get started

Usability Testing
-Have users interact with a system to identify flaws
-Typically a functional product

Conducted by:
Giving the user a scenario and a task to complete
Think aloud protocol
Answer questions
Debrief/ questionnaire

Data Collected:
Time to complete task

Additive mixing
combinations that increase the amount of light reflected (E.g. computer monitors)

Subtractive mixing
combinations that reduce the amount of light reflected (E.g. paint)

Perceptual Organization
– perceive distinct objects
– blind spot filled with spatial information
– how brain determines what pieces in the visual field go together

Object of focus

Surrounding area

Contrast Sensitivity
– distinguish bright and dim components of a static image
– function of both the contrast and the spatial frequency of what is being viewed

Opponent Process Theory
– theory of color vision, color perception is controlled by the activity of two opponent systems: blue-yellow and red-green
– process of excitatory and inhibitory responses

Visual Acuity
– clearness or sharpness of vision
– Snellen Eye Chart

the short wavelength (blue) cones do not contain cyanolabe

the long wavelength (red) cones do not contain the erythrolabe

the medium wavelength (green) cones do not contain chlorolabe

Color Blindness
– 1 in 12 men
– dichromatic (missing one photopigment)

CIE Color Space
Commission Internationale de l’Eclairage, describes colors based on three primaries

Color Circle
Gradient developed by Isaac Newton, all dimensions of hue and saturation in rainbow (add luminance makes ALL COLORS)

Eye Cones
Blue: Short wavelength receptors
Photopigment: cyanolabe
Green: Medium wavelength
Photopigment: chlorolabe
Red: Long wavelength
Photopigment: erythrolabe

Trichromatic Theory
– In humans, any hue can be matched with a combination of three primary colors
– 3 types of cones are 3 different photoreceptors: red, blue, green

property of color, variation described by names

purity, vividness, richness of color

Experimental research cont.
Due to the restricted nature of laboratory experiments, we-designed experiments have high internal validity
But…. strict control results in low ecological validity

Between subjects experiments
-Two or more groups of people are tested and each group received only one of the treatment conditions of the independent variable
-Typically random assignment
-Matched designs are better

similar elements (in terms of color, form, or orientation) are perceived together

Common region
artificially induce grouping with an explicit boundary

points connected in straight or smoothly curving lines are perceived together

Depth Perception
Used to translate physiology and a 2D image on the retina into 3D spatial information
Depth information: occulomotor and visual

artificially induce grouping with explicit lines

Occulomotor cues
proprioceptive: accommodation and convergence

Common fate
elements moving in the same direction at the same speed are perceived as together

automatic adjustments of the lens that maintain a focused image on the retina, good for stimuli between 20cm and 3m

nearer objects will block the view of more distant objects if they are in the same line of vision

the “bigness” of an object

angles such as when you know something is rectangular but it appears trapezoidal

Motion Parallax
apparent displacement or difference in position of an object viewed along two different lines of sight

Binocular Depth Cues
can only be perceived with two eyes

Object motion
– external object is moving
– with a single stimulus moving in a stationary background, we can detect movement as slow as 0.5mm per second

Perception of sound
– Longer sounds are perceived as louder than shorter sounds, diminishes when constant
-audible pitch and range decreases throughout lifetime

critical bandwidth
If intensity is constant, loudness is not affected by an increase in range of frequencies until CRITICAL BANDWIDTH

If a sound is audible by itself but not in the presence of other sounds

Sound localization
– the ability to locate sounds in space
– need 2 ears, interaural
– horizontal (not vertical) sound location
– intensity differences from sound shadow of head
ex. Doppler Effect

Vestibular System
inner ear, provides information on the direction gravity is pulling and your own acceleration, works with vision and proprioception to control movements

Somesthetic System
sense of touch, pressure, vibration, temperature, pain, and proprioception

Sensory system
receptors in skin, muscles, joints

Somatosensory cortex
Somatosensory cortex
– Adjacent areas in the skin are adjacent in the cortex
– More sensitive areas have larger areas in the cortex

Absolute threshold for touch
– smallest amount of touch that is detected, vary across the body
– Lowest absolute threshold is on the face

Two-point thresholds
– obtained by asking participants if they can determine the distance between two stimuli on their skin, when they are perceived as one stimuli then they are below the two-point threshold
– Lowest two-point threshold is in the fingers

Passive touch
the skin is stationary and an external pressure stimulus is applied to it

punctate touch

Active touch
person contacts the stimulus by moving the skin

Temperature perception
– Temperature sensitivity has an almost perfect temporal and spatial summation over large areas
– If you press a heated flat surface on your skin, it will feel hotter than if you just press the edge
– A hot object will feel hotter if it touches you longer until you experience adaptation

olfactory epithelium
Receptor cells in the nasal cavity

Summary of the Senses
– Audition is much like vision
– Constructed around cues provided by many sensory sources
– Vestibular sense is related to audition and provides us with information about our orientation and spatial relations in an environment
– Skin senses provide touch, temperature, and pain perception
– Chemical senses allow us to perceive different tastes and smells
– Errors in our perceptions can come from false or misleading stimuli, lack of context, and discrepancy from expectancies
– Need to minimize ambiguity and conform to expectancies

unit for measuring sound based on Stevens’ Law

Auditory Sensory System
An auditory stimulus initiates a complex sequence of events that lead to the perception of sound:
– Physical vibrations of the eardrum, ossicles, and oval window produce a wave motion in the fluid of the inner ear
– This wave motion causes neural signals through the bending of hair cells in the basilar membrane
– The auditory information is transmitted along pathways in which the neurons respond to different frequencies and other acoustic features
– The processing of the sensory signal performed by the auditory system provides the basis for auditory perception

Size and shape constancy
– We tend to see objects as the same size despite how large the image on our retina (close not giant)
– We tend to perceive objects as the same shape even the image on the retina may be a different shape

Apparent motion
discrete jumps of retinal images can produce the appearance of smooth motion

Induced motion
– a stationary background causes movement to be attributed to the wrong part of a scene
– after staring at a waterfall, other objects appear to be moving up

Binocular disparity
each eye receives a slightly different image of the world because of the eye’s location ex. stereogram

Monocular depth cues
Convey impressions of depth in a still image: interposition, size, perspective, motion parallax,

degree to which the eyes are turned inward to maintain fixation on an object, good up to 6m

open curves are perceived as complete forms

elements close together are perceived as a group

Use visual presentation if the…
Message is complex
Message is long
Message will be referred to later
Message deals with location in space
Message does not call for immediate action
Auditory system of the person is overburdened
Receiving location is too noisy
Person’s job allows remaining in one position

Some people have impaired vision or hearing sooooo….
Good to use more than one display modality when possible
Ex. Fire trucks and other emergency vehicles

Static displays
are fixed and do not change
Ex. Road signs

Character size influences legibility
Size necessary depends on the contrast ratio, viewing distance, environmental factors like ambient lighting, etc.

Some fonts will be more legible than others

The font “Clearview” was developed specifically for improving road signs
Increases the ability to differentiate between words
People recognize words at a 16% greater distance
When traveling 55 mph this is an additional 2 seconds

Alphanumeric Displays
When used in variable settings they need to be

Symbolic displays
are used to convey information by using an image
Typically concrete objects that can easily be drawn

More complex or abstract concepts are not so easy to represent symbolically
Good for overcoming a language barrier
Best if standardized

Must be identifiable and understandable
Even when people can recognize the object or concept, they may not be able to comprehend the message

The speed and accuracy with which people can identify symbolic displays are influenced by :
Gestalt organizational principles

Clear figure-ground distinction helps eliminate ambiguity about the important elements of the display
Simple and symmetric symbols will enhance readability
Closed, solid figures are easier to interpret than more complex, open figures
Figure contours should be smooth and continuous, unless discontinuity contributes to the information

Alphanumeric or Symbolic?
Reading is a highly over-learned process for literate people fluent in the language
Pro: No new relationships between symbols and concepts need to be learned
Con: Interpreting the message takes more cognitive resources

Symbolic displays can depict the intended information directly
Pro: People can interpret symbolic signs faster than alphanumeric signs
Pro: Requires less cognitive resources
Con: More susceptible to misinterpretation

In degraded viewing conditions people are much faster with symbolic displays

Legibility and readability are not critical for symbolic displays

Some situations require a combination of symbols and words

When combined, people pay more attention as long as they follow proper design principles

Coding dimensions
-Arbitrary features can be coded to objects or concepts

-Can be based on alphanumeric forms, non-alphanumeric forms, colors, sizes, flash rates, etc
Ex. Road signs are categorized by colors: green for road information, brown for sites of historic or recreational interest, blue for availability of services like food and gas, yellow for warnings, white signs are regulatory, and red are for stops or forbidden areas

-Appropriateness of coding dimension depends on the task or situation

Absolute judgment
refers to the classification of a stimulus when several options are available
Ex. Deciding that a signal is “high” when the options are high, medium, or low

If the stimulus varies on a single dimension, people can discriminate between 5 and 7 stimuli

relative judgments
directly compare one to another

Color Coding
is a method that can be very effective:
Especially when the color is unique
Ex. Searching for Washington apples in a basket of oranges vs. searching for tangerines in a basket of oranges

-Can be used to distinguish between different levels and kinds of information
Ex. Reading a map, roads are black and rivers are blue
Allows people to focus on one thing because they can ignore the other colors

Shape coding
is a useful method because people can distinguish between a very large number of geometric shapes
E.g. road signs:

Combination codes
are used to maximize discrimination ability between displays; using more than one type of coding in a display

If you want to know the best coding to use, then it depends on your situation:
Numeral and color codes are best for people who are new to the display
Experienced people are not affected by the type of coding

Dynamic Displays
All of the principles from static displays apply
Information is conveyed by movement within the display
The user must perceive changes in the state of the system as the display changes

two types of dynamic displays:
Analog: have a continuous scale and a pointer
Digital: present information in alphanumeric form

analog displays
Analog displays can be designed in 2 ways
Moving pointer and a fixed scale
Ex. Speedometer
Fixed pointer and a moving scale
Ex. Compass

digital displays
Digital displays only present the current value to the measure
Ex. Odometer

Analog or Digital?
Best type will not be the same in all situations

Digital display pro:
Convey exact numerical values well
Digital display cons:
Difficult to read when measurements are changing rapidly
Harder to see trends in the measurements (like if you are accelerating)

Analog display pro:
Convey spatial information and trends efficiently
Analog display con:
Do not provide precise values

As a general rule, digital displays are more appropriate for devices in which the measurements are not changing rapidly
Ex. Clocks or thermometers

Analog Displays
-Moving pointer with a fixed scale displays are very common and will usually be easiest for people to use

-Best for depicting changes from user input

-Need to consider whether to use labels or symbols to mark the scales
Scale units
How to mark them
What type of pointer to use

-All depend on the range of values and type of information

To make signs more efficient, ???????? words, symbols, colors, and locations should be used when available

Alphanumeric displays
are any display that uses words, letters, or numbers to convey information

Very common

Some letters and digits share many features and are easily confused with each other
The person viewing the display is assumed literate
Must keep in mind legibility and readability

For practical purposes, a display should have ????????? or be constructed of appropriate material for the environment

There should be ????? on important words

Dynamic displays
change over time
Ex. Speedometer

Legibility is also affected by the contrast between figures and their background
Contrast is determined by the amount of light reflected by the figures on the display
Dark print on a white background or light print on a dark background are best

describes how the message in the display should be unambiguous and include information about consequences if ignored

concerns larger groups of characters (e.g. words, sentences) in which comprehension of the material is a consideration

Readability is distinct from legibility!
In simple terms: legibility concerns the way text looks, while readability concerns its content or meaning

Legibility distance
is the distance at which a person can read the display
Good contrast increases legibility distance
Ex. Fluorescent street signs are more legible than non-fluorescent street signs of the same color in both daylight and night time conditions

how well the display attracts attention

-the ease with which the symbols and letters present in the display can be discerned, i.e. how easy it is to distinguish individual letters/symbols so that they can be recognized
-Influenced by factors like size of the letters, stroke width of the lines comprising letters, font
-Legibility for images on computer displays are affected by the pixel density

how well the display can be seen

Use auditory presentation if the…
Message is simple
Message is short
Message will not be referred to later
Message deals with events in time
Message calls for immediate action
Visual system of the person is overburdened
Receiving location is too bright or dark
Person’s job requires continual motion

most displays are:
visual or auditory

Designing Displays
-Well-designed displays insure the safe and effective operation of the system
-Design considerations are important in both complex and simple situations
Especially when lives are at stake like in a power plant or a plane cockpit
-Designs should be related to principles from human perception

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