Transcript Lecture 4

IE 486 Work Analysis & Design II
Instructor: Vincent Duffy, Ph.D.
Associate Professor
Lecture 4 – Perception: Other Senses & Information
Processing
Tues. Jan. 30, 2007
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For Review of Chapter 4 Visual Sensory Systems
Q.1 Give an example where missed visual signals can
contribute to human error.
Q.2. Briefly describe the difference between luminance and
illuminance.
Q.3. What are some properties of the visual receptor
systems?
Q.4 How can redundancy help in design? What can be
reduced through this design improvement?
Q.5. Briefly explain ‘top down’ vs. ’bottom up’ processing.
Q.6. Smaller cars are more likely to be hit from behind.
True or false? Why?
Q.7. Give an example in which an understanding of depth
perception can be used to improve road design.
Q.8. What is influenced by our limitations in visual sensory
systems?
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An overview – other sensory systems
1. An example of a workplace error & noise
 2. Sound, an auditory stimulus
 3. Alarms
 4. The trouble with sound transmission
 5. Noise revisited
 6. Noise remediation
 7. Other senses: touch and vestibular
 8. Conclusions

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1. An example of a workplace error & noise
Worker increasingly frustrated by noise
Unpleasant, stressful, and ringing in ears at the end
of the day
Could not hear emergency alarm on her own
equipment which nearly led to an injury
Didn’t wear earplugs because…
– they’re uncomfortable
– less likely to hear the alarm,
– more difficulty talking with other workers
not a safety issue in this case, more of a social
issue.
– “One of the few ‘pleasures’ on the job.”
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2. Sound, an auditory stimulus
The example illustrates three different types of
sounds
– Undesirable noise
– Critical ‘tone’ of the alarm
– Communications through speech
Discussions then included
– The role of sound in alarm
– The role of voice in speech communication
– The role of noise
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2. Sound, an auditory stimulus
Sound intensity can be measured by a sound
intensity meter.
The C scale weights all frequencies nearly equally.
Eg. Sound pressure levels in dB
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140 dB – jet at take-off
100 dB – subway train
70 dB – average auto; loud radio
60 dB – normal conversation
50 dB – quiet restaurant
20 dB – whisper
10 dB – normal breathing
0 dB – threshold of hearing
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2. Sound, an auditory stimulus
Intense sound can lead to hearing loss at some
frequencies
– Loudness maps to intensity
– Pitch maps to frequency
– Perceived location maps to location
Loudness is a ‘psychological’ experience that
correlates with ‘physical’ measurement of sound
intensity
– but it is not identical to that measurement
– Psychophysical scaling: An 80 dB sound does not
sound twice as loud as a 40 dB sound.
And an increase from 40 to 50 dB will not be
judged as the same loudness increase as a
change from 70 to 80 dB.
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2. Sound, an auditory stimulus
However, as an approximation, we can say that
loudness doubles with each increase of 10 dB in
sound intensity.
You may also consider that 85-90 dB is a point at
which potential danger to the ear can occur.
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3. Alarms
Effectiveness of alarms depends a bit on a good
understanding of the human auditory processing
(and the design context).
– by the designer
Good news: alarms are ‘omnidirectional’.
– Unlike visual signals, we can sense an auditory alarm
no matter what our physical orientation is.
– Auditory alarms induce a greater level of compliance
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3. Alarms
Problem with auditory alarms is illustrated in the
following:
– Flying when ‘peaceful revelry’ was shattered by the
audio stall warning, the stick shaker and warning
lights
The effect was not what was intended.
– I was frightened for several seconds and drawn away
from my instruments trying to cancel the audio/visual
assault
rather than just taking what should have been
instinctive actions.
“It was impossible to talk to the other crew member
and action had to be taken to cancel the alarms
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before addressing or fixing the problem.”
3. Criteria for Alarms
Must be heard above the background noise.
Should not be above the danger level for hearing.
Should not be overly startling
– (eg. Use a rise time)
Should not disrupt the processing of other signals or
other necessary speech communication
– Addressing this criteria necessitates a careful task
analysis under conditions which the alarm might
sound
and any necessary communications that might
occur as a consequence of the alarm.
Should be informative:
signal nature of the emergency & possibly future
actions
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4. The trouble with sound transmission
Tragic illustration of communication breakdown
– Tenerife airport in Canary Islands – 500 people
died
Ok, standby for takeoff and I will call
Was misinterpreted as
Okay…takeoff.
How does this relate to chapter 4?
Bottom up processing: sensory quality
Vs. Top down processing: expectations or
desires
Here loss of signal (bottom up quality) produced
inappropriate top-down processing
Heard what he wanted to hear.
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4. The trouble with sound transmission
Arguably the most important type of auditory
communication
Human speech
The female voice is more vulnerable to masking
Masking: when one sound can not be heard
due to presence of another
Consonants are more susceptible to masking,
but transmit more information than vowels.
– Eg. Consider mixing up ‘fly to’ with ‘fly through’.
Listening to synthetic speech takes more mental
resources than natural speech
Hence it could interfere with other concurrent
tasks
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5. Noise revisited
It is a potential health hazard in the workplace.
– It is an irritant and can mask other important sound
Noise-induced hearing loss can also show up in the
form of a ‘temporary threshold shift’.
– A ‘carry-over’ effect.
If a worker steps away from a machine to a quieter
place to answer a phone, they may still have some
difficulty hearing due to the previous recent noise
exposure.
Potential for ‘permanent’ hearing loss
– Triggered the need for remediation and development
of ‘permissible exposure levels’.
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6. Noise remediation

Signal enhancement
Eg. 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.
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6. 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 when
 Who will listen to them
 Who must listen to them
 What is cost to task performance, listener health
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7. Other senses: touch and vestibular
Typically play less of a role in system design
Consider touch and feel
– Gloves must be designed with sensitivity to
maintain tactile feedback as needed
Such feedback can provide spatial and
symbolic information for the blind – eg. braille
Whole-body orientation & motion-vestibular
Lets you know if you are ‘accelerating’ even with
your eyes closed
Important for vehicle simulators and virtual
environments
– Lack of body motion can create motion sickness and
illusions
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8. Conclusions
Audition, vision and other senses can provide an
overwhelming amount of information
Good designers can capitalize on strengths and
avoid the weaknesses provided by our senses.
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Information processing model (p.122)
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2. Information processing models
Perceptual Encoding
– includes issues of chapter 4 & 5 on senses
– Bring knowledge to the sensory input; give it meaning
Central Processing
– Includes concerns about ‘attentional resources’ and
issues related to perception, memory and thoughts
about the need for decision making – related to chapter
6
Responding
– The line between decision making and problem solving
is a bit blurred
– Includes decision making – chapter 7
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