11

Instructor: Vincent Duffy, Ph.D.Instructor: Vincent Duffy, Ph.D.

Associate ProfessorAssociate Professor

Lecture 4 – Perception: Other Senses & Information Lecture 4 – Perception: Other Senses & Information ProcessingProcessing

Tues. Jan. 30, 2007 Tues. Jan. 30, 2007

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

22

For Review of Chapter 4 Visual Sensory SystemsFor Review of Chapter 4 Visual Sensory Systems

Q.1 Give an example where missed visual signals can contribute Q.1 Give an example where missed visual signals can contribute to human error. to human error.

Q.2. Briefly describe the difference between luminance and Q.2. Briefly describe the difference between luminance and illuminance. illuminance.

Q.3. What are some properties of the visual receptor systems? Q.3. What are some properties of the visual receptor systems? Q.4 How can redundancy help in design? What can be reduced Q.4 How can redundancy help in design? What can be reduced

through this design improvement? through this design improvement? Q.5. Briefly explain ‘top down’ vs. ’bottom up’ processing. Q.5. Briefly explain ‘top down’ vs. ’bottom up’ processing. Q.6. Smaller cars are more likely to be hit from behind. True or Q.6. Smaller cars are more likely to be hit from behind. True or

false? Why? false? Why? Q.7. Give an example in which an understanding of depth Q.7. Give an example in which an understanding of depth

perception can be used to improve road design. perception can be used to improve road design. Q.8. What is influenced by our limitations in visual sensory Q.8. What is influenced by our limitations in visual sensory

systems? systems?

33

An overview – other sensory systemsAn overview – 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. Alarms4. The trouble with sound transmission4. The trouble with sound transmission5. Noise revisited5. Noise revisited6. Noise remediation 6. Noise remediation 7. Other senses: touch and vestibular7. Other senses: touch and vestibular8. Conclusions8. Conclusions

44

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

Could not hear emergency alarm on her own equipment Could not hear emergency alarm on her own equipment which nearly led to an injurywhich 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.”

55

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

The example illustrates three different types of The example illustrates three different types of soundssounds– 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

66

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

Sound 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

77

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

Intense sound can lead to hearing loss at some Intense sound can lead to hearing loss at some frequenciesfrequencies– Loudness maps to intensityLoudness maps to intensity– Pitch maps to frequencyPitch maps to frequency– Perceived 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 intensity with ‘physical’ measurement of sound intensity – but it is not identical to that measurementbut it is not identical to that measurement– Psychophysical scaling: An 80 dB sound does not sound Psychophysical scaling: An 80 dB sound does not sound

twice as loud as a 40 dB sound.twice as loud as a 40 dB sound.And an increase from 40 to 50 dB will not be judged as And an increase from 40 to 50 dB will not be judged as the same loudness increase as a change from 70 to 80 the same loudness increase as a change from 70 to 80 dB.dB.

88

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

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

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

99

3. Alarms3. Alarms

Effectiveness of alarms depends a bit on a good Effectiveness of alarms depends a bit on a good understanding of the human auditory processing understanding of the human auditory 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 alarm Unlike visual signals, we can sense an auditory alarm

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

1010

3. Alarms3. Alarms

Problem with auditory alarms is illustrated in the Problem with auditory alarms is illustrated in the following:following:– Flying when ‘peaceful revelry’ was shattered by the audio Flying when ‘peaceful revelry’ was shattered by the audio

stall warning, the stick shaker and warning lightsstall 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 rather than just taking what should have been instinctive actions.instinctive actions.

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

1111

3. Criteria for Alarms3. Criteria for Alarms

Must be heard above the background noise.Must be heard above the background noise.Should not be above the danger level for hearing.Should not be above the danger level for hearing.Should not be overly startling Should not be overly startling – (eg. Use a rise time)(eg. Use a rise time)

Should not disrupt the processing of other signals or Should not disrupt the processing of other signals or other necessary speech communicationother necessary speech communication– Addressing this criteria necessitates a careful task analysis Addressing this criteria necessitates a careful task analysis

under conditions which the alarm might sound under conditions which the alarm might sound and any necessary communications that might occur as and any necessary communications that might occur as a consequence of the alarm.a consequence of the alarm.

Should be informative: Should be informative: signal nature of the emergency & possibly future actionssignal nature of the emergency & possibly future actions

1212

4. The trouble with sound transmission4. The trouble with sound transmission

Tragic illustration of communication breakdownTragic illustration of communication breakdown– Tenerife airport in Canary Islands – 500 people diedTenerife airport in Canary Islands – 500 people died

Ok, standby for takeoff and I will callOk, standby for takeoff and I will call

Was misinterpreted asWas misinterpreted asOkay…takeoff.Okay…takeoff.

How does this relate to chapter 4?How does this relate to chapter 4?Bottom up processing: sensory qualityBottom up processing: sensory qualityVs. Top down processing: expectations or desiresVs. Top down processing: expectations or desiresHere loss of signal (bottom up quality) produced Here loss of signal (bottom up quality) produced inappropriate top-down processinginappropriate top-down processing

Heard what he wanted to hear. Heard what he wanted to hear.

1313

4. The trouble with sound transmission4. The trouble with sound transmission

Arguably the most important type of auditory Arguably the most important type of auditory communicationcommunication

Human speechHuman speech

The female voice is more vulnerable to maskingThe female voice is more vulnerable to maskingMasking: when one sound can not be heard due to Masking: when one sound can not be heard due to presence of anotherpresence of another

Consonants are more susceptible to masking, but Consonants are more susceptible to masking, but transmit more information than vowels.transmit more information than vowels.– Eg. Consider mixing up ‘fly to’ with ‘fly through’.Eg. Consider mixing up ‘fly to’ with ‘fly through’.

Listening to synthetic speech takes more mental Listening to synthetic speech takes more mental resources than natural speech resources than natural speech

Hence it could interfere with other concurrent tasks Hence it could interfere with other concurrent tasks

1414

5. Noise revisited5. Noise revisited

It is a potential health hazard in the workplace.It is a potential health hazard in the workplace.– It is an irritant and can mask other important soundIt is an irritant and can mask other important sound

Noise-induced hearing loss can also show up in the form Noise-induced hearing loss can also show up in the form of a ‘temporary threshold shift’.of a ‘temporary threshold shift’.– A ‘carry-over’ effect.A ‘carry-over’ effect.

If a worker steps away from a machine to a quieter If a worker steps away from a machine to a quieter place to answer a phone, they may still have some place to answer a phone, they may still have some difficulty hearing due to the previous recent noise difficulty hearing due to the previous recent noise exposure.exposure.

Potential for ‘permanent’ hearing loss Potential for ‘permanent’ hearing loss – Triggered the need for remediation and development of Triggered the need for remediation and development of

‘permissible exposure levels’.‘permissible exposure levels’.

1515

6. Noise remediation6. Noise remediation

Signal enhancementEg. Redundancy. Face to face communication is

more effective than when the listener can not see the speaker

Listener can see the lips moving Noise reduction at the source

Can be achieved through careful selection of tools Environmental noise

Death rate from heart attacks of elderly residents near LAX was significantly higher than the rate in a demographically equivalent area without excessive noise from takeoff and landing of aircraft.

1616

6. Noise remediation6. Noise remediation

Not all noise is bad.Eg. Soft noise can help mask the loud ticking of a

clock at night. Task analysis is important in considering:

What sounds will be present whenWho will listen to themWho must listen to themWhat is cost to task performance, listener health

1717

7. Other senses: touch and vestibular7. Other senses: touch and vestibular

Typically play less of a role in system designTypically play less of a role in system design

Consider touch and feelConsider touch and feel– Gloves must be designed with sensitivity to maintain Gloves must be designed with sensitivity to maintain

tactile feedback as neededtactile feedback as needed

Such feedback can provide spatial and symbolic Such feedback can provide spatial and symbolic information for the blind – eg. brailleinformation for the blind – eg. braille

Whole-body orientation & motion-vestibularWhole-body orientation & motion-vestibularLets you know if you are ‘accelerating’ even with your Lets you know if you are ‘accelerating’ even with your eyes closedeyes closed

Important for vehicle simulators and virtual environmentsImportant for vehicle simulators and virtual environments– Lack of body motion can create motion sickness and illusions Lack of body motion can create motion sickness and illusions

1818

8. Conclusions8. Conclusions

Audition, vision and other senses can provide an Audition, vision and other senses can provide an overwhelming amount of informationoverwhelming amount of information

Good designers can capitalize on strengths and Good designers can capitalize on strengths and avoid the weaknesses provided by our senses.avoid the weaknesses provided by our senses.

1919

Information processing model (p.122)Information processing model (p.122)

2020

2. Information processing models2. Information processing models

Perceptual EncodingPerceptual Encoding – includes issues of chapter 4 & 5 on sensesincludes issues of chapter 4 & 5 on senses– Bring knowledge to the sensory input; give it meaningBring knowledge to the sensory input; give it meaning

Central ProcessingCentral Processing– Includes concerns about ‘attentional resources’ and Includes concerns about ‘attentional resources’ and

issues related to perception, memory and issues related to perception, memory and thoughtsthoughts about the need for decision making – related to chapter about the need for decision making – related to chapter 66

RespondingResponding– The line between decision making and problem solving The line between decision making and problem solving

is a bit blurredis a bit blurred– Includes decision making – chapter 7Includes decision making – chapter 7