Process of seeing | Visual Capability| Workstation Design | Workplace Design |Types of Display | Gaurav Singh Rajput

Process of seeing | Visual Capability|
Workstation Design | Workplace
Design |Types of Display
By: Gaurav Singh Rajput
@gauravkrsrajput

VISUAL CAPABILITIES
Basic visual system gives rise to several visual
capabilities that have important implications for the
design of visual displays.
 Accommodation
 Visual Acuity
 Contrast Sensitivity
 Adaptation
 Color Discrimination
 Perception

Accommodation
 Ability of the lens of the eye to focus the light rays
on the retina.
 Allows us to see details of an object, such as
reading, fine print on a contract or identifying a
person across the street.
 There are limits on the degree to which the lens can
accommodate objects.
 Eg: if you try to focus the text on this page while
bringing the page slowly toward your eyes, there
will be a point at which the image becomes blurred
and the eyes cannot clearly focus it.(near point)

Accommodation
 Near point: closest distance to which the eyes can
focus
 Far point: beyond which the eyes can not clearly
focus
 In normal vision, the far point is usually near infinity
 Dark focus: accommodative state to which the eyes
tend to move spontaneously in darkness
 For a normal eye, the dark focus is about at arm's
length
 Accommodation is a compromise between the
position of the stimulus to be focused and an
individual's dark focus.

Visual Acuity
 Ability to discriminate fine detail and depends
largely on the accommodation of the eyes.
 There are different types of visual acuity
depending on the type of target and detail one is
asked to resolve.
 Most commonly used measure of acuity:
minimum separable acuity,
 It refers to the smallest feature or the smallest
space between the parts of a target that the eye
can detect.

Visual Acuity
 Various targets are used in measuring minimum
separable acuity including letters and various
geometric forms

Adaptation
Changes in our sensitivity to light are called
adaptation
In the dark, the sensitivity of the visual system
increases over time and we can see dimmer
and dimmer objects.
This process of dark adaptation takes place in
two phases.
First phase takes about 5 min and represents
the adaptation of the cones
Second phase takes about 30 to 35 min and
represents the adaptation of the rods.

Contrast Sensitivity
Spatial frequency: number of bars per unit
distance.
Spatial frequency is usually measured in terms
of cycles per degree of visual angle where one
cycle would be a black bar plus a white bar
(compare fig. e and f)
As you move a grating farther away or make the
bars narrower the spatial frequency of the
grating increases.

Factors Affecting Visual Acuity
and Contrast Sensitivity
 Luminance Level : acuity and contrast sensitivity
increase with increasing levels of light or
background luminance (lightness) and then level
off.
 With higher levels of light, the cones are
activated, resulting in higher acuity and sensitivity.
 Contrast : When the contrast between a visual
target and its background is low, the target must
be larger for it to be equally discriminable as a
target with greater contrast.

Exposure Time: under high illumination
conditions, acuity improves with increased
exposure time up to 100 or 200 ms and then levels
off.

 Target Motion :The movement of a target or the
observer (or both) decreases visual acuity.
 Ability to make visual discriminations under such
circumstances is called dynamic visual acuity.
 Age: visual acuity and contrast sensitivity
declines with age. The decline generally begins
after age 40 and is continuous throughout the rest
of life.
 Training: improvements in dynamic visual acuity
with practice.

Color Discrimination
 cones in the retina (fovea) are responsible for our
perception of color.
 three types of cones, each sensitive to a range of
wavelengths of light that centre on those that
correspond to one of the primary colors (red, green,
and blue)
 when comparing color defectives with normals on
such practical tasks as judging signal lights at sea,
sorting color-coded electronic components, or
identifying and reacting to traffic signals, color
defectives' performance is always poorer than
normals' performance

Perception
Involves the sensing of stimuli
Concerns primarily the interpretation of that
which is sensed.
In visual displays it depends on previous
learning as by experience and training
Eg:learning shapes of road signs, color codes
of electric wiring systems, abbreviations on a
computer keyboard, implications of the zigs
and zags of an electrocardiograph recording
or even the simple recognition of letters of the
alphabet.

Perception
 design should meet two objectives:
i. the display must be able to be seen clearly
ii. design should help the viewer to correctly
perceive the meaning of the display
 displays are designed for specific work situations
 adequate training of workers to interpret the
meaningfulness of the specific display indications
is needed; but appropriate design should
capitalize on those display features that help
people to understand the meaning that is, to
perceive correctly what they sense.

VDT WORKSTATION DESIGN GUIDELINES

WORKSTATIONS
The objective is to:
• Fit the workstation to the employee
• Reduce awkward positions
This can be done by using two methods:

WORKSTATIONS CONT.
Standard Way
– Adjustable
workstation
– Adjustable chair
– Foot rests
– Adjustable monitor
– Document holder
Innovative Way
– Cut legs off
– Add blocks
– Build foot rest
– Thick book
– Build platform

EXERCISES & STRETCHES
These are exercises or stretches that can be
performed at your workstation, home, just
about anywhere.

DISPLAYS
 Purpose of Displays - convey information about a
certain entity in our environment or surrounding
 Visual Displays - display information to the sight
sense
• Conspicuous (attention getting)
• Legible (easy to see and detect)
• Understandable (tells you state of the entity or
required action to take)
• Main problem: this sense is overloaded

DYNAMIC DISPLAYS
 Quantitative Readings: used to read a precise
numeric value
eg: “The pressure is 125 psi”
 Qualitative Readings: used to read an approximate
value or rate of change, or change in direction.
eg: “The pressure is rising”

DYNAMIC DISPLAYS
 Check Readings: to determine if parameters are
within some "normal" bounds or that several
parameters are equal.
eg: “All pressures are normal”
 Situation Awareness: to perceive and attach
meaning to elements in a volume of time and space
and to project the status of the elements into the
near future
eg: an air traffic controller, looking at a radar display.

DESIGN OF DISPLAYS
 It is critical that all the information needs of the user
be fully understood otherwise result is an incomplete
information
 For all, the display type should be chosen based on the
task
 New displays should be tested and evaluated

Basic Design of Quantitative Displays
 Conventional quantitative displays
1. Fixed scale with moving pointer -Analog
2. Moving scale with fixed pointer-Analog
3. Digital display
• Conventional-moving mechanical parts
• Modern- electronically generated features,
eliminating need for moving mechanical parts

Comparison of Designs
 Digital displays are generally superior to analog displays
under the conditions
 a precise numeric value is required
 the values presented remain visible long enough to be
read
• Digital displays are better in both accuracy of reading and
preference
Analog Displays are useful when:
• the values are subject to frequent or continual change
• it is important to observe the direction or rate of change of
the values presented

Comparison of Designs
 Fixed scale moving pointer displays are useful for
values subject to frequent and continual change
 A pointer moving against fixed scale is better
 When range of values is greater, moving scale fixed
pointer display is used
 Circular and semicircular scales are better over
horizontal and vertical scale

Features of Quantitative Displays
 Scale range: numerical difference between the
highest and lowest values on the scale
 Numbered interval: numerical difference between
adjacent numbers on the scale
 Graduation interval: numerical difference between
the smallest scale markers
 Scale unit: smallest unit to which the scale is to be
read

Numeric Progressions of Scales
 numeric progression system characterized by
graduation interval of the scale
 progression by 1s (0, 1, 2 etc) - easiest to use
 progression by 5s - satisfactory
 progression by 25s – moderate to use
 decimals- difficult to use
 unusual progression systems (3s, 8s, etc) should be
avoided

Quantitative scale with numeric
progression system
g: Graduation interval value-
difference between the minor
markers
n: Numbered interval value-
difference between numbered
markers

Length of Scale Unit
 Length on the scale (in inches, mm, or degrees of arc)
that represents the numeric value that is the smallest
unit to which the scale is to be read.
 Eg: if a pressure gauge is to be read to the nearest 10
lb and the scale is so constructed that a 0.05 inch
represents 10 lb of pressure, then the length of scale
unit is 0.05 inch

Design of Pointers
 Use pointed pointers
 have the tip of the pointer meet, but not overlap
 colour of the pointer extend from the tip to the
centre of the scale(circular scales)
 have the pointer close to the surface of the scale

Scale Size and Viewing Distance
 Normal viewing distance of 28 in (71 cm).
 If a display is to be viewed at a greater distance, the
features have to be enlarged in order to maintain at
the eye, the same visual angle of the detailed
features.
 To maintain that same visual angle for any other
viewing distance(x in inches)
Dimension at x in= (dimension at 28 in) X (x in/28)

Designs of a meter
 one at the right would be easier
 it is bolder and less cluttered
 has fewer graduation markers
 the double arc line has been eliminated
 scale length is increased by placing the markers
closer to the perimeter

Different display types
 The choice of the type of display must be based on a
thorough understanding of the nature of the task
confronting the user.
 Object displays: when integration of information is
required
 Separate displays: in which user needs to focus on
specific variables

Different display types
 The design of object displays may prove to be as
much of a creative art as a systematic science
 The display configuration should be tested with
subjects representative of the ultimate users under
task conditions likely to be experienced in the real
world.

QUALITATIVE VISUAL DISPLAYS
 For some continuously changeable variable
(temperature, pressure, speed or rate of change)
 eg: to know temperature of car’s engine- qualitative
reading by providing engine-temperature gauge
 basic underlying data used for such purposes usually
are quantitative.

Design of Qualitative Scales
 many qualitative scales represent a continuum of
values that are sliced into a limited number of ranges
(cold, normal, and hot)
 specific ranges have particular importance to the
user (representing a danger zone)
 perception of the correct reading is aided by some
method of coding the separate ranges
 one method – using color codes

Design of Qualitative Scales
 Another method-use some form of shape coding to
represent specific ranges of values
(caution, undesirable)
 Quantitative displays with coded zones also can be
used to reflect trends, directions and rates of change.
 Further, they can be used for quantitative reading if
the scale values are included.

Check Reading
 Refers to the use of an instrument to ascertain
whether the reading is normal
 Eg: providing second hand in wrist watch to check
whether watch is working or not
 If several or many instruments for check reading are
used together in panels, their configuration should
be such that any deviant reading stands out from the
others.
 advantage of such a systematic alignment is based on
human perceptual processes

Check Reading
 the human tendency to perceive complex
configurations as complete entities, with the result
that any feature that is "at odds" with the
configuration is immediately apparent

Status Indicators
 qualitative information indicates the status of a
system or a component
 use of some displays for check reading to determine
if a condition is normal or abnormal
 the qualitative reading of an automobile
thermometer to determine if the condition is hot,
normal, or cold.

Status Indicators
 status indications reflect separate, discrete
conditions such as on and off or (traffic lights) stop,
caution, and go
 commonly used status indicators are lights, such as
traffic lights
 redundant codes - with most traffic lights that are
coded both by color (red, yellow, and green) and by
location (top, middle and bottom)

SIGNAL AND WARNING LIGHTS
Flashing or steady-state lights are used for
various purposes, such as
• indications of warning (as on highways)
• identification of aircraft at night
• navigation aids and beacons
• to attract attention

Detectability of Signal and
Warning Lights
Factors influence the detectability of lights
– Size, Luminance, and Exposure Time
– Colour of Lights
– Flash Rate of Lights

Context of Signal Lights
 situational and environmental variables can influence
people's awareness of signal lights
 Eg:roof-mounted, rotating-beam emergency
lights(ambulances and police cars)
 due to different lights there will be different results
 whether vehicle was moving
 to indicate the direction and whether it was moving
fast or slow.

Context of Signal Lights
•blue lights to be seen as moving toward
•red ones were seen more often as
moving away

Recommendations Regarding Signal and
Warning Lights
 When should they be used?
• To warn of an actual or a potential dangerous
condition
 How many warning lights?
• Ordinarily only one
 Steady state or flashing?
• to represent a continuous, ongoing condition, use a
steady-state light
• continuous flashing lights can be distracting. To
represent occasional emergencies or new conditions,
use a flashing light.

Recommendations Regarding Signal
and Warning Lights
 Flash rate: 3 to 10 per second (4 is best) with equal
intervals of light and dark
 Warning-light intensity: twice as bright as the
immediate background
 Location: within 30° of the operator's normal
line of sight
 Colour: normally red because red means danger to
most people.
 Size: subtend at least 1° of visual angle

REPRESENTATIONAL
DISPLAYS/SITUATION AWARENESS
 Purpose: to enhance operators' situation awareness.
 depict changeable conditions
 consist of elements that tend to change positions or
configuration superimposed on a background
 Eg: aircraft display that shows positions of other
aircraft in the sky and terrain features on the ground.
 Eg: CRT displays used in medical laboratory

REPRESENTATIONAL

REPRESENTATIONAL
 Involves matching information received from our
senses & from displays to pre learned situational
templates
 Allow us to understand the situation and predict what
is likely to happen
 Eg: stream of red taillights in the distance might match
a schema you have in long term memory that tells you
that you will be slowing down

Effects of colour in design of displays
 People have strong tendency to perceive similarly
colored objects as belonging together
 Used for conceptual grouping of text in a planned
route, timetables etc
 Eg: station names can be represented in one colour,
destination in another, departure & arrival times in
third colour.

 Red- to “stop” or “danger”
 Green – “go” or mean that system is running
normally
 Orange – “caution”
 5%-8% people have colour vision defects (colour
blindness)
 Most common deficit is inability to distinguish
between red & green(they both look brown!)

Auditory Displays
Voice input to humans(by machines) is a
very powerful visual modality
Nature of auditory sensory modality offers
certain unique advantages for presenting
information as contrasted with visual
modality.

Auditory displays
 Circumstances in which auditory displays would
preferable to visual displays:
 When the origin of the signal is itself a sound
 When the message is simple and short
 When the message will not be referred to later
 When the message deals with events in time
 When warnings are sent or when the message calls
for immediate action
 When a verbal response is required

Auditory displays
 When continuously changing information of some
type is presented, such as aircraft, radio range, or
flight-path information
 When the visual system is overburdened
 When speech channels are fully employed (in which
case auditory signals such as tones should be clearly
detectable from the speech)
 When illumination limits use of vision
 When the receiver moves from one place to another

Human functions involved in the
reception of auditory signals:
 Detection :determining whether a given signal is
present, such as a warning signal
 Relative discrimination :differentiating between two
or more signals presented close together
 Absolute identification :identifying a particular signal
of some class when only one is presented
 Localization: determining the direction from which
the signal is coming

Masking
 Condition in which one component of the sound environment
reduces the sensitivity of the ear to another component
 Operationally defined, masking is the amount that the
threshold of audibility of a sound (the masked sound) is raised
by the presence of another (masking) sound.
 In studying the effects of masking, an experimenter typically
measures the absolute threshold (the minimum audible level)
of a sound to be masked when presented by itself and then
measures its threshold in the presence of the masking sound.

Masking
 The difference is attributed to the masking effect
 In selecting a particular auditory signal for use in a
particular environment, we must consider the
masking effect of any noise on the reception of that
signal
 The effects of masking vary with the type of masking
sound and with the masked sound itself-whether
pure tones, complex sound, white noise, speech, etc.
 The greatest masking effect occurs near the
frequency of the masking tone and its harmonic
overtones

Masking
 With low-intensity masking tones (20-40 dB) the
masking effect confined to the frequencies around
that of the masking tone
 With higher-intensity masking tones (60 to 100 dB),
the masking effect spreads to higher frequencies
 The masking of pure tones by narrowband noise
 In the masking of pure tones by wideband noise, the
primary concern is with the intensity of the masking
noise in a "critical band" around the frequency of the
masked tone

Masking
• The size of the critical band is a function of the
center frequency, with larger critical bands
being associated with higher frequencies

Principles of Auditory Display
1. General principles
A. Compatibility: the selection of signal dimensions
and their encoding should exploit learned or natural
relationships of the users
-like high frequencies associated with up or high and
wailing signals with emergency

B. Approximation: Two-stage signals should be
considered when complex information is to be
presented
(1) Attention-demanding signal: to attract attention and
identify a general category of information.
(2) Designation signal: designate the precise
information within the general class indicated by the
first signal.

C. Dissociability: Auditory signals should be easily
discernible from any ongoing audio input (be it
meaningful input or noise)
• Eg: if a person is to listen concurrently to two or
more channels, the frequencies of the channels
should be different
D. Parsimony: Input signals to the operator should not
provide more information than necessary
E. Invariance: Same signal should designate the same
information at all times.

2. Principles of presentation
A . Avoid extremes of auditory dimensions: High-
intensity signals, for eg: can cause a scare response
and actually disrupt performance
B. Establish intensity relative to ambient noise level:
The intensity level should be set so that it is not
masked by the ambient noise level.

C. Use interrupted or variable signals: avoid steady-
state signals and use interrupted or variable signals.
This minimizes perceptual adaptation.
D. Do not overload the auditory channel: A few
signals should be used in any given situation. Too
many signals can be confusing and will overload the
operator.

3. Principles of installation of auditory displays
A. Test signals to be used: made with a representative sample of
the potential user population to be sure the signals can be
detected and discriminated by them
B. Avoid conflict with previously used signals: Any newly
installed signals should not be contradictory in meaning to
any somewhat similar signals used in existing or earlier
systems.

C. Facilitate changeover from previous display: Where
auditory signals replace some other mode of
presentation (eg.visual), preferably continue both
modes to help people become accustomed to the
new auditory signals .

Auditory Displays for Specific Purposes
• Warning and Alarm Signals
 Useful for signalling warnings and alarms
 Different responses for different signals
 Increase in signal intensity results faster reaction
times
 Intensity level of warning devices should chosen with
concern for the response requirements placed on the
operator

Design of warning and alarm signals
• Recommendations
 Use frequencies between 200 & 5000 Hz, preferably
between 500 & 3000 Hz because the ear is most
sensitive to this middle range.
 Use frequencies below 1000Hz when signals have to
travel long distances (over 1000 ft), because high
frequencies do not travel as far.
 Use frequencies below 500 Hz when signals have to
"bend around" major obstacles or pass through
partitions

Design of warning and alarm signals
 Use a modulated signal (1to 8 beeps per second)
 Use signals with frequencies different from those
that dominate any background noise, to minimize
masking.
 If different warning signals are used to represent
different conditions requiring different responses,
each should be discriminable from others
 Use a separate communication system for warnings,
such as loudspeakers, horns etc.

Advantages of Auditory Displays
 More alerting than visual displays
 “Eyes free” and “hands free” capturing attention
during performance of other tasks
 Suitable when message is short and need not be
referred to later
 Useful to communicate with people working in dark
place(mines) or at night

CONCLUSION
 Careful design of visual and auditory display reduces the
possibility of information overload and ensures that the
information is presented in an effective manner.
 In designing an easy to interpret interface, the needs of
the user must be supreme
 Applications of auditory and visual displays present great
opportunities to further help people work in complex
environments.

Process of seeing | Visual Capability| Workstation Design | Workplace Design |Types of Display | Gaurav Singh Rajput

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