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HUMAN FACTORS IN ENGINEERING & DESIGN

Chapter II: INFORMATION INPUT

Topics:

Information Input & ProcessingVisual Displays

Auditory Displays

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INFORMATION INPUT & PROCESSING

Sources & pathways of stimuli:

Human being is bombarded with all sorts ofstimuli from outside environment & within thehuman body the input is received as stimuli& processed by the brain

Not all stimuli received can be sensed cansense only those within spectra of sensitivity.

Sources could be from distant or close light,sound, thermal, mechanical, chemical.

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Sensory channels or Pathways:

Exteroceptors: Vision, Audio, Smell, Taste &Touch receptors of stimuli generatedexternal to the body.

Ability to see & hear etc. Proprioceptors: Receptors of stimuli

generated within the body embedded within

the internal tissues muscles, tendonsaround joints, inner ear etc

Ability to reach out, making a sudden turn etc.

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External stimuli within the range of humansensitivity excites the appropriateexteroceptor on a selective basis lightexcites visual channel.

External stimuli provides data that aresensed by the human receptors

Human attaches a meaning to what is

sensed called Perception Sensing of stimuliData;

Perception of stimuli sensedInformation

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Special category of Proprioceptors :

Kinestheticreceptors

Clustered primarily around joints

Primarily to tell us where our limbs are atgiven point of time, to co-ordinate movementand sense forces developed by our muscles.

Gives the feedback necessary for limb

movement where such a sense is required inconduct skilled tasks rather than visuallydependent tasks

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INFORMATION THEORY

Information Theory: It provides an operationaldefinition to Information & an quantitative methodof measuring it.

Concept: Information results in reduction ofuncertainty.

The occurrence of highly certain events conveyless info as they confirm what was expected.

Eg: Fasten Seat Belt! indicator comes on each

time the car is started, while Oil Level Lowindicator is unexpected even, but, both areimportant.

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Unit of measure of Information:

Info Theory measures info in bits.

A bit of information is the amount ofinformation required to decide between twoequally likely alternatives.

INFORMATION THEORY

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INFORMATION THEORY

When the probabilities of occurrence of alternatives

are equal, then,

Information, H = Log2 N . where N is numberof alternatives.

With 2 equally likely alternatives,

Information, H = Log2 2= 1 bit. With 4 equally likely alternatives,

Information, H = Log2 4= 2 bits. A randomly chosen digit from 0 - 9 would convey,

Information, H = Log2 10= 3.322 bits. A randomly chosen alphabet from A - Z would convey,

Information, H = Log2 26= 4.7 bits.

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INFORMATION THEORY

When the probabilities of occurrence of alternatives areunequal, then,

Information, hi = Log2 (1/pi)

where hi is the info associated with event i.

pi

probabilityof occurrence of that event i

. When Average information of series of events are

to be found,

Average Information,

]p

1[logph

1i

2i

N

1iave

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INFORMATION THEORY

100]1[)(max

Xh

hPercentageREDUNDANCY av

Max possible info is obtained when alternatives are

equally likely to occur, when there is departure fromequal probability the greater is the reduction in theinfo from the max.

This is termed as Redundancy in information.

English language has degree of redundancy with th &

qu occurring more frequently in combination than others.

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INFORMATION INPUT PROCESSES

Only a small fraction of info sensed can be

processed based on the Bandwidth of thecommunication channel.

Bandwidth gives the rate of info transmission over

the channel or pathway measured in bits/sec.

Pathway Estimated bandwidth (bits/sec)

Normal human Ear 8,000 to 10,000Visual nerve fibre (Eye) 1,000

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But, these are higher than the human brain can

possibly absorb, interpret & analyze.

Much of what is received at the peripheral senses isfiltered out before it reaches the brain for obtaining a

response.Process Max Flow of Info Bits/Sec

Sensory registration

At nerve junctionsConscious level

Long-Term store

1,000,000,000

3,000,00016

0.7

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After sensing, processing to take placesmoothly for optimum performance.

In some, the correlation between input &output is quite obvious such as readinstructions & operate a simple hand tool,while in others it could be difficult to correlate

remote control of a complex process.

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Reaction Time to Stimulus:

Hick experiment in1952:(Choice reaction time expt)A person to make discrete & separate response todifferent stimuli (on Information theory) to push oneof four buttons depending on which of the four color

lights come on Red, Blue, Green, Yellow.

Hick varied the number of stimuli in the reaction timetask and found that Reaction time increased as the

number of equally likely alternatives increased.

Plot of Mean Reaction Time versus Number ofstimuli in bits indicated a linear relationship.

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Reaction Time to Stimulus:Hyman experiment in1953:(Choice reaction time expt) Altered the stimulus information without changing

the number of alternatives but changing theprobability of occurrence of alternatives.

Reaction time was stilla linear function of Stimulusinformation.

This is called the Hick-Hyman Law, which provesthat information theory is applicable to Informationprocessing.

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TYPES OF INFORMATION

Human info & processing depends on Stimuli

Original source of Stimuli object, event,environment condition

Information may come:

Directly:Observation of event itself.Indirectly:Through intervening media radar, telescopic.

Info maybeCoded visual / auditory displays

or Reproduced: Photograph, TV, Radio ormicroscopes, telescopes, binoculars intentionallyor unintentionally magnified / modified enlarged,amplified, filtered for easier processing.

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TYPES OF INFORMATION- Classification

Static: Fixed over a period of time printed or

written charts, graphs, signs. Dynamic: Changes with time continuously radar,

Speedometer, temperature gauges.

Also classified as:

Quantitative: Values of variables indicated - speedQualitative: Trend, direction, value of change.

Status Information: Displays status ON or OFFWarning & Signal Info: Gives emergency & unsafeconditions static or dynamic signboard or siren

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TYPES OF INFORMATIONClassification Contd.

Representational Info: Pictorial or Graphic

representation of area or object maps, charts,blueprints.

Identification Info: To identify some static conditionsituation or objectColor-coded pipes, traffic signals.

Alpha-Numeric & Symbolic Info: Presentation ofverbal, numeric or related coded info Signs,Placards, Braille, music notes.

Time-Phased Info: Presentation of pulsed or time-phased signals Morse codes, Blinker lights ofdirect dialing Tele billing equipment.

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STAGES OF INFO PROCESSING(Working of the Sensorimotor)

FEEDBACK

WorkingMemory

Long-TermMemory

MEMORY

Short TermSensory Store

PerceptionDecision

&

Response Selection

ResponseExecution

STIMULI RESPONSE

Attention Resources or

Motivation

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Working of the Sensorimotor

Short-Term Sensory Store / Memory:

Temporary memory channel erases or fades away aftershort period after stimuli has ceased.

Helps in perceiving stimuli.

It holds the data in as is condition without coding & hence

cannot go into the working memory.

Types:

Iconic storage: Associated with visual system (about a sec)

Echoic storage: Associated with auditory system (a few sec)

S

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Working of the Sensorimotor

Working Memory:

Encodes & transfers info from sensory storage to workingmemory

Requires direct attention to the process.

Coded in 3 ways:

Visual: Visual representation of stimuli.

Phonetic: Auditory representation of stimuli.

Semantic: Abstract representation of stimuli.

Picturize the object by hearing the sound or code the soundfrom the visual representation of the object.

Phonetically coding of sound generated from word DOG.

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Working Memory:

Stimulus Codes

Sensory Working Memory LT Memory

Auditory

Visual

Echoic PhoneticSemantic

Iconic Visual

Semantic (abstract) coding helps optimal LT term storage.

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Working Memory

Capacity limited and decays if not properly coded.

For better retention, the items are clubbed to formchunks.

Max number of items that can be held in working

memory 7 2 chunks ( 5 or 9 chunks).E.g.: A string of items in 9 chunks a.t.o.g.t.a.c.r.d can be

better retained as cat,dog,rat with 3 chunks.

Rules: Avoid presenting more than 9 chunks.

Present in meaningful & distinct chunks.

Provide training on how to recall info.

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Long Term Memory

Info from working memory is transferred to LT

Memory by Semantically coding it. Supplying meaning to info & relate to info already

present in LT Memory.

Working memory info is analyzed, compared &related to past knowledge & stored into LT memoryto make retrieval easy Mnemonics makesretrieval easy. It involves picking up first letter of a

item and frame words/sentence to make itmeaningful. This can be recalled more easily.

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Perception

Short term sensory store helps perception stimuli

sensed & carried to central mechanism to beprocessed

Depends on past experience, training, background

& conditioning.

Process is flexible human being an infotransmitter or sometimes a info processor

(Eg. Typist copying document)

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Choice of Response

Decision on choice of response is dependent on

working memory & also effected by individual biases. Ones experience, expectations, previous processing

steps etc may lead to a decision to select a response.

Response could be manipulative, conversation, grossbody movements (running) etc.

Response is enhanced by attentionresource/motivation at all levels of processing.Attention could be divided, focused, selective orsustained.

Feedback helps effective response & improveperformance.

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Parameters effecting Performance

Frequency of signals increase the better

Strength of signals stronger the better

Discriminate signals from non-signals

Periodic feedbacks to operator

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Biases in Decision Making

Undue importance to early info or evidence.

Human generally conservative. Do not extract as much infoas they optimally should.

As more info is gathered, people become more confident

and finally overconfidence and wrong decisions.

Humans have limited ability to analyze manyconcepts/hypothesis at a time.

People treat all info to be equally reliable even though theyare not.

Att ti R

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Attention Resources

Task of paying attention is directed to objects oractivities so that they can be perceived and

recalled.

Depending upon situation, Attention is:

Selective Attention:A pilot looking for a deviant reading as he scans theinstruments. Ability to detect a deviate signal in 5different dials or in 1 dial, with signals rate of 25 perminute.

1 dial better than 5 as it reducesLoadStressRate of signal presented brings inSpeedStress

Att ti R

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Attention Resources

Focused Attention:

Maintaining attention one or few channels of infoand not be distracted by other channels of info.

Proximity to source one visual source of info andcompletely ignore another if the two are within 1degree of visual angle from each other.

In auditory the proximity could be the wavelength

to be maintained as distinct for better performance.

Att ti R

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Attention Resources

Divided Attention: (Time-sharing)

When people are required to do more than one task at atime, performance on at least one of the tasks oftendeclines.

Humans have limited capacity to process info when several

tasks are performed simultaneously, this capacity can beexceeded.

Sustained Attention:

The ability to maintain attention and remain alert to stimuli

over prolonged periods of time.Gained importance where humans assume role of systemmonitor where he has to observe dials, screens for criticalsignals that may demand action.

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VISUAL DISPLAYS

The process of seeing

When to use visual displays

Quantitative & Qualitative displays Basic designs of visual displays

Guidelines to visual displays

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The Process of Seeing

We depend on vision to gather informationabout the state of environment outside static or dynamic. The capacity is limited.

Light is visually evaluated radiant energy asmall spectrum of this energy is visible tohuman eye.

About 80 % of info acquired by humans isthrough the visual channel.

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Human Eye - features

Eye globe is of about 2.5 cms diameter.

Six muscles attached to eyeball through ligamentsenables eyeball move left-right, roll-in roll-out. Visible light rays pass through an transparent

covering in front called Cornea into the anteriorchamber. It is then focused with a lens on a photosensitive area.

Anterior chamber has fluid - Aqueous Humor, withoptical properties to bend the rays.

Inner chamber has fluid Vitreous Humor, thicker

in density but same optical property. Two chambers inside eyeball separated by the Iris

and the lens.

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Pupil is an variable aperture within the Iris.

Pupil gets larger in darker surroundings and smaller inbrighter conditions to admit adequate light rays into the eye.

Together with the vitreous humor and the adjustable lensthe light is brought to a focus on the Retina.

Retina is an outgrowth of the brain. Retina contains Nervous tissues called Neurons.

Neurons make up most of the Retina and is composed ofPhotoreceptors called Rods and Cones.

Cones respond to light levels equivalent to light falling on awhite paper 30 cm (1 feet) away from a standard candleand above. This is termed as daylight vision (PhotopicVision)

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Rods are receptors for low illumination or Scotopic

Vision. They respond to lower illumination levelsequivalent to light impinging on earth on full moonnight or below.

Combination of cones and rods are used during in-

between levels of illumination (Mesopic Vision). Retina has 2 distinct regions Fovea and Optic

Disk.

Fovea is a shallow pit rich in cones, centeredwithin the yellow spot. Hence, has the maximumvisual acuity sharpness.

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Rods concentration peaks +/- 20 degrees off the

Fovea. For best vision during lower illuminationone has to look about 20 degrees off the intendedtarget to get the most of it.

Optic Disk is the exit point from Retina that makethe Optic nerve. This disk is free of receptors andis effectively blind, hence called the BlindSpot.

Sclera, tough outer tissue protects eye structure.

The tissue layer called Choroids Membrane,between the Retina & Sclera, is dark in color toabsorb light not taken up by the Retina.

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The curvature of Lens is controlled by the Ciliary

Muscles together with Suspensory ligaments. Relaxation of muscles thickens the lens to bring the

nearby objects within the focus of the Retina.

Contraction of muscles flattens the lens to bring the

far off objects within the focus of the Retina. The altering of lens for proper focusing is called

Accommodation.

Image on the Retina is inverted & reversed.

Inverted image signals are taken by nervous systemto the brain. The brain interprets image as reverseas what is received, thus giving the correct picture.

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Human Eye & the Camera

Differences:

1. Eye lens is in fixed position & need not moveback & forth to focus, unlike a camera. Hence,faster than camera.

2. Human film sensitivity is varied & capable ofcapturing image at variety of illumination, while acamera film has a specific illumination necessary.

3. Eye can see in 3 dimension while a camera in 2dimensions.

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Visual Capabilities1. Accommodation:

Ability of lens to focus on to the retina.

Helps read details of object.

Accommodation between Near & Far point.

In normal vision, Far Point is at infinity (20& more).

Far Point is the distance beyond which the eyecannot clearly focus.

Near Point is the closet distance to which the eyecan focus . Depends on human age as agingoccurs the distance increases.

A d ti C td

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Accommodation Contd.

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Accommodation Contd.

The focal points & Distances are expressed in

Diopters, D = 1/object distance, in metres.

The lens is specified in Diopters.

Higher the Diopter, more powerful the lens and its

ability to bend the light rays. Accommodation capacity inadequate leads to

NearsightednessImage focused in front of the retinaExternal lens concave

FarsightednessImage focused beyond the retina

External lens convex.

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Visual Capabilities

2. Convergence:

Act of aiming both eyes at the same point.

Average time required to aim the eyes &

focus them to a new point displaced in adistance is about 165 Milliseconds.

In case reading it, average time 200milliseconds at same distance, while at 20feet & more it is lesser.

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Visual Capabilities

3. Saccadic Eye Movement:

Co-ordinated motion of both eyes together.

A movement of over a space of 5 letters inordinary print at a space of 1 feet is about 15

20 M Sec.

converted to angle 20 degrees of eyemovement corresponds to 4 inchs at adistance of 1 feet.

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Visual Capabilities

Saccadic Eye Movement:

Rate of increase of eye movement increaseswith angle & then reduces after certain angle.

Extent of movement(Degrees)

Duration of movement (M.Sec)

10 40

20 55 1530 80 25

40 100 20

Visual Capabilities

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Visual Capabilities4. Color Discrimination:

Cones receive rays with higher illumination are of 3 types

whose wavelengths correspond to the primary colors red,blue & green.

Darker conditions no color observed as cones do notoperate.

Trichromats - Normal color vision

Monochromats - Color blind

Dichromats - Red or Blue cone deficient (8% Males 0.5% Females)

Red deficient cannot distinguish between shades of Red &Orange

Blue deficient cannot distinguish between shades of Blue &Yellow

Red deficient perform worser than blue deficient ones.

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Visual Capabilities5. Visual Acuity: (Resolving Power of eye)

Ability to discriminate fine details. It is minimum separable distance.

Smallest feature that the eye can measure.

Depends largely on accommodation of the eyes.

Also depends on: The object itself

Distribution of radiant energy

Illumination of the background

Contract between object & background Duration of visual stimulus

Acuity better under Photopic light than Scotopiclight conditions.

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Visual Capabilities5. Visual Acuity: (Resolving Power of eye)

Acuity is the inverse of the visual angle subtendedat the eye by the smallest detail that can besubtended.

If a person can discriminate a detail that subtends an arc of1.5 minutes, the Acuity Score is 0.67 (1/1.5).

A person with better acuity has a score higher than 0.67.

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Visual Capabilities

Visual Acuity: (Contd.)

In industrial environment, the visual Acuityis checked every 2 years inspectionsections etc.

Tests for Acuity include Letter targets,Checkerboards, Gratings etc.

Vi l C bili i

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Visual Capabilities

6. Depth Perception: Special form visual acuity is the ability to see

depth.

Two eyes enables seeing at different angles. Ability to see depth for distant objects is less

compared to near objects.

Eg. Crane operators require good depth perception.

Vi l C biliti

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Visual Capabilities6. Purkinje Shift:

Eye sensitive at different wavelengths of light. Sensitivity of vision depends on the wavelength for Scotopic

& Photopic intensity.

The light-adapted eye (Photopic) is maximally sensitive to

light with a wavelength of 555 nm.(1 nm = 10-9 m)

Color: Greenish Yellow

The dark-adapted eye (Scotopic) is maximally sensitive to

light with a wavelength of 505 nm.Color: Yellowish Green

The shift from 555 to 505 nm is Purkinje Shift.

Vi l C biliti

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Visual Capabilities6. Purkinje Shift (Contd.):

Vi l C biliti

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Visual Capabilities7. Optical Illusion:

Optical illusions from perceptions of visual stimuligenerate errors need to minimize such errorswhile designing visual displays.

Optical Illusion

VISUAL DISPLAYS
http://newillusions.ppt/http://newillusions.ppt/

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VISUAL DISPLAYS

Keeping in view of the visual capabilities the

visual displays are designed in terms oftexts, graphics, symbols & codes static ordynamic.

Displays to be made so that all info isunderstandable.

Requires the displays to be readable, &

signals detectable.

VISUAL DISPLAYS

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VISUAL DISPLAYS

Visual displays classified as:

Quantitative displays

Qualitative displays

Check ReadingsSituation Awareness (Representational)

VISUAL DISPLAYS

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VISUAL DISPLAYS

Quantitative displays:

Provides info about value of some variable.Basic designs are:

1. Fixed scale with moving pointer

2. Moving scale with fixed pointer

3. Digital displaysAnalog indicators conventionally have mechanical movingparts, while modern technology makes it possible forelectronically generated features eliminating need for

moving mechanical components.

1. Fixed scale with moving pointer:

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Digital Displays (Counters)

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Superior to analog displays

Applicable when:Precise numeric value is required.

Values presented remain visible long enough & not

changing continuously. Counters may be mechanically operated or

electronically generated signals.

Digital Displays (Counters)

2 26 9 354 5

Guidelines: Selection of analog displays

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Guidelines: Selection of analog displays

Pointer moving against Fixed scale is

preferred. Natural interpretation of events to be

addressed ; Eg. Thermometer.

Not advisable to mix types of pointer scaleindicators to avoid reversal errors in reading.

Small variations better indicated in MovingPointer fixed scale.

For large range of values moving scale &fixed pointer is preferred.

Scale patterns implying Good & Bad designs

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p p y g g

Qualitative Displays

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User interested in approximate value of

continuously changing variable.

Rate of change, know the trend.

Quantitative data may be used as a basisfor qualitative reading in 3 ways:

Determine status or condition (Temp)

Maintain desirable range (Speed)

Observe rate of change or trend (Altitude)

Comparison of types of scales

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Comparison of types of scalesType Average Reading Time,

millisecondsQualitative Quantitative

Open-Window 115 102

Circular 107 113

Vertical 101 118

Vertical scale best for Qualitative reading

Open-window with shortest time for Quantitativedigital displays

Circular windows best for Qualitative digital displays

Design of Qualitative Scales:

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g

Users can be made to perceive qualitativedisplays using:

Color Coding

Shapes Coding

Qualitative Scales

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Qualitative Scales

Color Coding

Qualitative Scales

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Shapes Coding:

Shape coding immediately conveys meaning.

Experimentation on Aircraft instrument

readings on number of designs to 140military cadets to analyze.

Experimentation on Aircraft instrument

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p


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3. Check Readings:

Use of instrument to ascertain whetherreading is normal or not.

Normal reading pointer aligned at 3 or 12

Oclock position


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p y

4. Situation Awareness (Representational)

AUDITORY DISPLAYS

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Sound vibrations received by sense organ ear.

Sound created by any source.

Attributes of sound are Frequency & Amplitude (intensity).

With atmosphere to be source of vibrations,

Sinusoidal wave by simplesound generating sourceHigher

Lower

Normal Air Pressure

0 Time

Denser Rarer

Changes inair molecules

AUDITORY DISPLAYS

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Features of the sine wave:

Waveform above mirror image of waveform belowmidline.

Wave form pattern repeats itself in cycles.

Frequency is number of cycles per second , inHertz.

Human ear sensitive to frequencies in the range20 20000 Hz, though not equally sensitive.

Pitch is the highness or lowness in tone.When frequency lowers pitch/tone to be lowered.

Eff t f f ti

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Effect of frequency on perception

When changed in intensity, the following occurs:

Frequency Perception

Less than 1000 Hz Low frequency & high Pitch

More than 3000 Hz High frequency & low Pitch

Between 1000 -3000 Hz Stable, even if low Pitch

Intensity of sound

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y Intensity or Loudness is power per unit area.

Watts/m2.

As range of power values for commonsounds are high, it is convenient to use logscale.

The ratio of two sound pressures in decibelis frequently used:

Sound Pressure Level,dB = 20 log(P1/P

o)

Where P1 Sound pressure to be measuredPo Reference Sound pressure

Intensity of sound

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y

Sound Pressure Level,dB = 20 log10 (P1/Po)Where P1 Sound pressure to be measured

Po Reference Sound pressure

When P1 =Po, log10 1 is zero, indicates 0 dB

And Po cannot be zero, as dB becomes infinity.

Complex Sound Waves

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Very few sounds are pure.

Even musical sounds contains combinationof fundamental frequencies resulting in acomplex or composite waveform.

Individual sinewaves

Complex sinewaves (sum of

sine waves)

The Human Ear

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Anatomically ear has 3 divisions:

Outer Ear, Middle Ear & Inner Ear

The Outer Ear:

Pinna the external part

Auditory canal bayonet shaped tube 1 long &

Ear drum or Tympanic membrane ( at the end of canal).

Function: Collects sound energy

The Human Ear

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Middle Ear: Ossicles the 3bone structureTransmitsvibrations from the ear drum to the ovalwindow of the inner ear through Stapes a pistonform.

Can amplifysound waves up to 22 times

Muscles on Ossicles provide for time delayin caseof intense noise before muscles contract & transmit

vibrations (Gun Shot).

The Human Ear

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Inner Ear:

Spiral shaped, 30 mm when uncoiled & filled with fluid5-6 mm at the oval window end

Stapesacts as pistonpressurizes the fluid in the ovalwindow driving it back and forth, in response to

change in pressures at the ear drum

Basilar Membranewithin the inner ear vibrates due tochange in fluid pressure

Corti which has Auditory Nerve Cells pick up thevibrations of the basilar membrane and transmit thesignals to the brain through the Auditory Nerve.

The Human Ear

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When Auditory Displays used ?

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Origin of signal itself a sound

Visual system is over burdened

Speech channel is fully employed

Illumination limits use of visual displays

Receiver moves from one place to another

A verbal response is required

Message is short & simple

will be not referred to later

deals with events in time

calls for immediate action

continuously changing

Auditory displays not to be used, when:

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Noise levels exceed or are very near the

discomfort levels

Too many audio signals are being received

Noise from equipments etc are similar to

planned auditory display

Too many auditory signal types tends toconfuse the listener & he may orient himselfto one and ignore the others.

Human functions in Reception of Auditory signals

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Detection: To determine whether a givensignal is present

Relative discrimination: Differentiating 2 ormore signals presented close together. Just-Noticeable Differences (JND 60 dB above

absolute threshold)

Absolute Identification: Identify a particularsignal

Localization: Determine the direction fromwhich the emanates from.

Sound Level

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Risk of damage Level not acceptable

0

90

80

60

40

20

110

120

Threshold Hearing Barely audible sound

Whisper

Quiet Room (JND)

Conversation

In

Pneumatic Drill / Heavy Traffic / Car

Train (External)

Riveting

Thunder

Level above which pain is felt

Soun

d

PressureLevel

(SPL)

dB

Types of Auditory Displays:

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Range of Auditory displays:

Speech SignalsSingle word warnings

FIRE !

Standard messagesYOU ARE IN QUEUE

Extemporaneous message

WIND SW - 10 Knots


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Range of Auditory displays

Non Speech Signals: Bell, Buzzer, Horn,Siren, Tone &Electronic (Sonar & Echo)


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Displays maybe:

Direct : Person to Person ( Air conduction)Indirect : Loud speaker or Ear phone

Presented to one or both ears

If Ear phone is used one signal to each earor mix signals alternately

Just Noticeable Difference (JND) is the

smallest change or difference along astimulus that can just be detected 50 % of thetime by people

Special Purpose Auditory Displays:

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Warning & Alarm Signals: To have unique features to invoke quick response.

Signals to be in mid range of 500 3000 Hzfrequency as ear is most sensitive in this range.

When signal are to travel far (>1000 feet), use lowerfrequencies (

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Frequency was slowly from 400 to 925 Hz

Eight different warning signals tested for reaction time in differentenvironments and it results are as under:

Most effective: Yeow & Beep

Least Effective : Wail

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12 Easily Discriminating Warning Signals

Types of Auditory Equipments:

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When helmets are used then equipment to bedesigned without disturbing the position ofhelmet (Dought-nut type cushion)

Principles of Auditory Displays:

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Compatibility: Selection of signal encoding,frequency with the need. (Beep with emergency)

Dissociatibility: To be easily differentiated fromother audio signal (background)

Parsimony: Operator not to be providedinformation more than necessary

Invariance: Same signal to designate the sameinformation at all times

Principles of Presentation:

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Avoid extreme of auditory dimensions can

startle / disrupt performance Intensity be relative to ambient noise level

Use interrupted or variable signals avoid

steady state or continuous signal Do not over load auditory channel can

confuse the operator ( 60 signal types used in

nuclear crisis

HFED_2

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