Strategic Management

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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
• Didnt wear earplugs because
• theyre 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
• 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 before addressing or fixing the problem.

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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
• Okaytakeoff.
• 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