ie 486 work analysis & design ii vincent g. duffy, ph.d. associate professor school of...

IE 486 Work Analysis & Design IIIE 486 Work Analysis & Design II

Vincent G. Duffy, Ph.D.Vincent G. Duffy, Ph.D.Associate ProfessorAssociate Professor

School of Industrial Engineering School of Industrial Engineering and Department of Agricultural & Biological and Department of Agricultural & Biological

EngineeringEngineeringPurdue UniversityPurdue University

Tuesday, January 23, 2007 Tuesday, January 23, 2007 Lecture 3 - PerceptionLecture 3 - Perception

AdministrativeAdministrative

Lectures 1 & 2 available on course Lectures 1 & 2 available on course webpagewebpage: : //web.ics.purdue.edu/~duffy/index486//web.ics.purdue.edu/~duffy/index486

11stst lab meeting this Friday lab meeting this Friday– Lab sections revised Lab sections revised

Fri 8:30 KNOY B019;Fri 8:30 KNOY B019;Fri 10:30 KNOY B019Fri 10:30 KNOY B019Fri 1:30 GRIS 166Fri 1:30 GRIS 166Fri 3:30 GRIS 160Fri 3:30 GRIS 160

– Wickens text on reserve Wickens text on reserve – Freivalds text available in electronic catalogFreivalds text available in electronic catalog

Perception Perception

PerceptionPerception– Will be the lead element among ‘perception’, Will be the lead element among ‘perception’,

information processing’ and ‘decision making’ information processing’ and ‘decision making’ – See also fig. 6.1 on p.122 (an advanced look) See also fig. 6.1 on p.122 (an advanced look) – We will look first at ‘individual characteristics’We will look first at ‘individual characteristics’

Capabilities and limitations first in relation to Capabilities and limitations first in relation to

Visual Sensory Systems (ch.4 in Wickens et al. text)Visual Sensory Systems (ch.4 in Wickens et al. text)

An overview of capabilities & limitations of the An overview of capabilities & limitations of the Visual Sensory System related to designVisual Sensory System related to design

1. Missed visual signals – an example1. Missed visual signals – an example

2. Light stimulus – definitions2. Light stimulus – definitions

3. Visual receptor system – physiological 3. Visual receptor system – physiological issues issues

4. Top down vs. bottom up4. Top down vs. bottom up

5. Depth perception5. Depth perception

6. Conclusions6. Conclusions

11. 50 year old traveler – missed visual . 50 year old traveler – missed visual signals – an examplesignals – an example

Arrives by air to an unfamiliar cityArrives by air to an unfamiliar city– Dark rainy nightDark rainy night– Ready to pick up rental carReady to pick up rental car– Bus driver points to carBus driver points to car– Can’t tell if red or brown.Can’t tell if red or brown.– Climbs into wrong car firstClimbs into wrong car first

1. 50 year old traveler – missed visual 1. 50 year old traveler – missed visual signals – an examplesignals – an example

Arrives by air to an unfamiliar cityArrives by air to an unfamiliar city– Dark rainy nightDark rainy night– Ready to pick up rental carReady to pick up rental car– Bus driver points to carBus driver points to car– Can’t tell if red or brown.Can’t tell if red or brown.– Climbs into wrong car firstClimbs into wrong car first– then after finding correct car, pulls out city map to find then after finding correct car, pulls out city map to find

his way out of the airporthis way out of the airport– Cant see well in dim lightCant see well in dim light– Gives up map, confident he will see the correct sign to Gives up map, confident he will see the correct sign to

route 60route 60

1. An example – missed visual signals1. An example – missed visual signals

Looks for window wipersLooks for window wipers

Has difficulty reading text against gray Has difficulty reading text against gray interiorinterior

Turns on wipers and enters roadway slowlyTurns on wipers and enters roadway slowly– traffic rapidly closes in behind him, traffic rapidly closes in behind him, – bright glare of headlights in rearview mirror bright glare of headlights in rearview mirror

forces him to accelerate to uncomfortable speedforces him to accelerate to uncomfortable speed


Can’t read first sign properly– Route 60 or 66?Can’t read first sign properly– Route 60 or 66?– Misses exit on the left side of the highwayMisses exit on the left side of the highway

Turns on dome light,Turns on dome light, – frustrated, frustrated,

– reaches for map reaches for map

– head downhead down

– hears sound of gravel pavement hears sound of gravel pavement


Can’t read first sign properly– Route 60 or 66?Can’t read first sign properly– Route 60 or 66?– Misses exit on the left side of the highwayMisses exit on the left side of the highway

Turns on dome light,Turns on dome light, – frustrated, frustrated,

– reaches for map reaches for map

– head downhead down

– hears sound of gravel pavement hears sound of gravel pavement

before turning back onto highway lane,before turning back onto highway lane, – falls into huge pothole – Halt!falls into huge pothole – Halt!

2. Light stimulus2. Light stimulus

Illuminance – lighting qualityAmount of light that strikes the surface

Luminance - Light reflected off of a surface or object (that is not a light source)

2. Light stimulus2. Light stimulus

Illuminance – lighting qualityAmount of light that strikes the surface

Luminance - Light reflected off of a surface or object (that is not a light source)

Wickens suggests the light leaves some ‘il’ on the surface to provide a way to remember the differenceLuminance – what is left after the ‘il’ removed

3. Visual receptor system3. Visual receptor system

Different properties includeDifferent properties include– Location – direct in center or away from centerLocation – direct in center or away from center– Acuity - detail that can be resolvedAcuity - detail that can be resolved– Sensitivity – related to thresholdSensitivity – related to threshold– Color sensitivityColor sensitivity

At night only the rods are working, hence it is difficult to At night only the rods are working, hence it is difficult to distinguish color (under poorly lit conditions).distinguish color (under poorly lit conditions).


Different properties includeDifferent properties include– Location – direct in center or away from centerLocation – direct in center or away from center– Acuity - detail that can be resolvedAcuity - detail that can be resolved– Sensitivity – related to thresholdSensitivity – related to threshold– Color sensitivityColor sensitivity

At night only the rods are working, hence it is difficult to At night only the rods are working, hence it is difficult to distinguish color (under poorly lit conditions).distinguish color (under poorly lit conditions).

– AdaptationAdaptation – related to eye response to changing – related to eye response to changing conditionsconditions

– Differential wavelength sensitivityDifferential wavelength sensitivityre: the use of red and ability to see redre: the use of red and ability to see red

Red lamp can help read on ship deck without disrupting ability to Red lamp can help read on ship deck without disrupting ability to see faint light/objects in dark, see faint light/objects in dark,

but red objects look black at nightbut red objects look black at night


Color sensationColor sensation– Note: 7% of male population is color blind – Note: 7% of male population is color blind –

can’t tell the difference between red and greencan’t tell the difference between red and greenSuggested design for ‘monochrome’ firstSuggested design for ‘monochrome’ first

– Color can be used in ‘redundancy’Color can be used in ‘redundancy’Eg.? Eg.?

Traffic light – top, middle, bottomTraffic light – top, middle, bottom– Then red, yellow, greenThen red, yellow, green

4. Top down vs. bottom up processing4. Top down vs. bottom up processing

Influence the quality of information processingInfluence the quality of information processing

Eg. Experience and knowledge feed in from top Eg. Experience and knowledge feed in from top downdown

World and stimulus feed senses from bottom upWorld and stimulus feed senses from bottom up

Top down –Top down –suggests what should be theresuggests what should be there

Bottom up – Bottom up – signals what is theresignals what is there


Eberts and MacMillan (1985) showed higher than Eberts and MacMillan (1985) showed higher than average rate that small cars are hit from behindaverage rate that small cars are hit from behind– Because of the cue of relative size differenceBecause of the cue of relative size difference

Features of the world violate our expectations, but Features of the world violate our expectations, but top-down processing takes over and gives top-down processing takes over and gives inappropriate perception.inappropriate perception.


Eberts and MacMillan (1985) showed higher than Eberts and MacMillan (1985) showed higher than average rate that small cars are hit from behindaverage rate that small cars are hit from behind– Because of the cue of relative size differenceBecause of the cue of relative size difference

Features of the world violate our expectations, but Features of the world violate our expectations, but top-down processing takes over and gives top-down processing takes over and gives inappropriate perception.inappropriate perception.

Clever design applicationClever design application– Drivers overspeeding while approaching traffic circleDrivers overspeeding while approaching traffic circle– Denton (1980) drew lines of ‘diminishing separation’ on Denton (1980) drew lines of ‘diminishing separation’ on

the road to give the driver the increasing flow of texture the road to give the driver the increasing flow of texture past the driver (signaling an increase in speed) – top past the driver (signaling an increase in speed) – top down.down.

– Driver should instinctively slow to the safe speed.Driver should instinctively slow to the safe speed.

6. Conclusions6. Conclusions

We have limitations in our visual systemWe have limitations in our visual system There are top down influencesThere are top down influences

And Bottom upAnd Bottom up

Understanding of perceptionUnderstanding of perception & system goals & system goals can helpcan help

6. Conclusions on visual sensory systems6. Conclusions on visual sensory systems

Our limitations of our visual systemOur limitations of our visual system – Influence the information input and hence our Influence the information input and hence our

perceptionperception

Some top down influences includeSome top down influences include– Expectancy and learningExpectancy and learning

Some bottom upSome bottom up – Planned signalsPlanned signals

6. Conclusions on visual sensory systems6. Conclusions on visual sensory systems

Our limitations of our visual systemOur limitations of our visual system – Influence the information input and hence our Influence the information input and hence our

perceptionperception

Some top down influences includeSome top down influences include– Expectancy and learningExpectancy and learning

Some bottom upSome bottom up – Planned signalsPlanned signals

Information about perceptionInformation about perception – and understanding of the system goals and attributes and understanding of the system goals and attributes

can be used to help guide the design can be used to help guide the design of the displayof the display

Partial overview of other sensory systemsPartial overview of other sensory systems

1. An example of a workplace error & noise1. An example of a workplace error & noise2. Sound, an auditory stimulus2. Sound, an auditory stimulus3. Alarms3. AlarmsSee also ch.5 in Wickens textSee also ch.5 in Wickens text

1. An example of a workplace error & noise1. An example of a workplace error & noise

Worker increasingly frustrated by noiseWorker increasingly frustrated by noise

Unpleasant, stressful, and ringing in ears at the end Unpleasant, stressful, and ringing in ears at the end of the dayof the day

Could not hear emergency alarm on her own Could not hear emergency alarm on her own equipment which nearly led to an injuryequipment which nearly led to an injury

Didn’t wear earplugs because… Didn’t wear earplugs because… they’re uncomfortablethey’re uncomfortable

less likely to hear the alarm, less likely to hear the alarm,

more difficulty talking with other workers more difficulty talking with other workers

not a safety issue in this case, more of a social issue. not a safety issue in this case, more of a social issue. – ““One of the few ‘pleasures’ on the job.”One of the few ‘pleasures’ on the job.”

2. Sound, an auditory stimulus2. Sound, an auditory stimulus

The example illustrates three different The example illustrates three different types of soundstypes of sounds– Undesirable noiseUndesirable noise– Critical ‘tone’ of the alarmCritical ‘tone’ of the alarm– Communications through speechCommunications through speech

Discussions then included Discussions then included – The role of sound in alarmThe role of sound in alarm– The role of voice in speech communicationThe role of voice in speech communication– The role of noiseThe role of noise

2. Sound, an auditory stimulus2. Sound, an auditory stimulusSound intensity can be measured by a sound Sound intensity can be measured by a sound intensity meter. intensity meter.

The C scale weights all frequencies nearly equally.The C scale weights all frequencies nearly equally.Eg. Sound pressure levels in dBEg. Sound pressure levels in dB

– 140 dB – jet at take-off140 dB – jet at take-off

– 100 dB – subway train100 dB – subway train

– 70 dB – average auto; loud radio70 dB – average auto; loud radio

– 60 dB – normal conversation60 dB – normal conversation

– 50 dB – quiet restaurant50 dB – quiet restaurant

– 20 dB – whisper20 dB – whisper

– 10 dB – normal breathing10 dB – normal breathing

– 0 dB – threshold of hearing0 dB – threshold of hearing

2. Sound, an auditory stimulus2. Sound, an auditory stimulusIntense sound can lead to hearing loss at some frequenciesIntense sound can lead to hearing loss at some frequencies

Loudness maps to intensityLoudness maps to intensityPitch maps to frequencyPitch maps to frequencyPerceived location maps to locationPerceived location maps to location

Loudness is a ‘psychological’ experience that correlates Loudness is a ‘psychological’ experience that correlates

with ‘physical’ measurement of sound intensitywith ‘physical’ measurement of sound intensity but it is not identical to that measurementbut it is not identical to that measurementPsychophysical scaling: An 80 dB sound does not Psychophysical scaling: An 80 dB sound does not sound twice as loud as a 40 dB sound.sound twice as loud as a 40 dB sound.And an increase from 40 to 50 dB will not be judged And an increase from 40 to 50 dB will not be judged as the same loudness increase as a change from 70 as the same loudness increase as a change from 70 to 80 dB.to 80 dB.

2. Sound, an auditory stimulus2. Sound, an auditory stimulus

However, as an approximation, we can However, as an approximation, we can say that loudness doubles with each say that loudness doubles with each increase of 10 dB in sound intensity.increase of 10 dB in sound intensity.

You may also consider that 85-90 dB is a You may also consider that 85-90 dB is a point at which potential danger to the ear point at which potential danger to the ear can occur.can occur.

3. Alarms3. AlarmsEffectiveness of alarms depends a bit on a Effectiveness of alarms depends a bit on a good understanding of the human auditory good understanding of the human auditory processing processing

(and the design context).(and the design context).– by the designerby the designer

Good news: alarms are ‘omnidirectional’.Good news: alarms are ‘omnidirectional’.– Unlike visual signals, we can sense an auditory Unlike visual signals, we can sense an auditory

alarm no matter what our physical orientation is.alarm no matter what our physical orientation is.– Auditory alarms induce a greater level of Auditory alarms induce a greater level of

compliancecompliance

3. Alarms3. AlarmsProblem with auditory alarms is illustrated in Problem with auditory alarms is illustrated in the following:the following:

Flying when ‘peaceful revelry’ was shattered by the Flying when ‘peaceful revelry’ was shattered by the audio stall warning, the stick shaker and warning lightsaudio stall warning, the stick shaker and warning lights

The effect was not what was intended.The effect was not what was intended.I was frightened for several seconds and drawn away I was frightened for several seconds and drawn away from my instruments trying to cancel the audio/visual from my instruments trying to cancel the audio/visual assaultassault

– rather than just taking what should have been instinctive rather than just taking what should have been instinctive actions.actions.

– ““It was impossible to talk to the other crew member It was impossible to talk to the other crew member and action had to be taken to cancel the alarms and action had to be taken to cancel the alarms before addressing or fixing the problem.”before addressing or fixing the problem.”

ie 486 work analysis & design ii vincent g. duffy, ph.d. associate professor school of...

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