IE 486 Work Analysis & Design II

IE 486 Work Analysis & Design II Vincent G. Duffy, Ph.D. Associate Professor School of Industrial Engineering and Department of Agricultural & Biological Engineering Purdue University Tuesday, January 23, 2007 Lecture 3 - Perception

Administrative • Lectures 1 & 2 available on course webpage: //web.ics.purdue.edu/~duffy/index486 • 1st lab meeting this Friday • Lab sections revised • Fri 8:30 KNOY B019; • Fri 10:30 KNOY B019 • Fri 1:30 GRIS 166 • Fri 3:30 GRIS 160 • Wickens text on reserve • Freivalds text available in electronic catalog

Perception • Perception • Will be the lead element among ‘perception’, information processing’ and ‘decision making’ • See also fig. 6.1 on p.122 (an advanced look) • We will look first at ‘individual characteristics’ • Capabilities and limitations first in relation to • Visual Sensory Systems (ch.4 in Wickens et al. text)

An overview of capabilities & limitations of the Visual Sensory System related to design 1. Missed visual signals – an example 2. Light stimulus – definitions 3. Visual receptor system – physiological issues 4. Top down vs. bottom up 5. Depth perception 6. Conclusions

1. 50 year old traveler – missed visual signals – an example • Arrives by air to an unfamiliar city • Dark rainy night • Ready to pick up rental car • Bus driver points to car • Can’t tell if red or brown. • Climbs into wrong car first

1. 50 year old traveler – missed visual signals – an example • Arrives by air to an unfamiliar city • Dark rainy night • Ready to pick up rental car • Bus driver points to car • Can’t tell if red or brown. • Climbs into wrong car first • then after finding correct car, pulls out city map to find his way out of the airport • Cant see well in dim light • Gives up map, confident he will see the correct sign to route 60

1. An example – missed visual signals • Looks for window wipers • Has difficulty reading text against gray interior • Turns on wipers and enters roadway slowly • traffic rapidly closes in behind him, • bright glare of headlights in rearview mirror • forces him to accelerate to uncomfortable speed

1. An example – missed visual signals • Can’t read first sign properly– Route 60 or 66? • Misses exit on the left side of the highway • Turns on dome light, • frustrated, • reaches for map • head down • hears sound of gravel pavement

1. An example – missed visual signals • Can’t read first sign properly– Route 60 or 66? • Misses exit on the left side of the highway • Turns on dome light, • frustrated, • reaches for map • head down • hears sound of gravel pavement • before turning back onto highway lane, • falls into huge pothole – Halt!

2. Light stimulus • Illuminance – lighting quality • Amount of light that strikes the surface • Luminance - Light reflected off of a surface or object (that is not a light source)

2. Light stimulus • Illuminance – lighting quality • Amount 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 difference • Luminance – what is left after the ‘il’ removed

3. Visual receptor system • Different properties include • Location – direct in center or away from center • Acuity - detail that can be resolved • Sensitivity – related to threshold • Color sensitivity • At night only the rods are working, hence it is difficult to distinguish color (under poorly lit conditions).

3. Visual receptor system • Different properties include • Location – direct in center or away from center • Acuity - detail that can be resolved • Sensitivity – related to threshold • Color sensitivity • At night only the rods are working, hence it is difficult to distinguish color (under poorly lit conditions). • Adaptation – related to eye response to changing conditions • Differential wavelength sensitivity • re: the use of red and ability to see red • Red lamp can help read on ship deck without disrupting ability to see faint light/objects in dark, • but red objects look black at night

3. Visual receptor system • Color sensation • Note: 7% of male population is color blind – can’t tell the difference between red and green • Suggested design for ‘monochrome’ first • Color can be used in ‘redundancy’ • Eg.? • Traffic light – top, middle, bottom • Then red, yellow, green

4. Top down vs. bottom up processing • Influence the quality of information processing • Eg. Experience and knowledge feed in from top down • World and stimulus feed senses from bottom up • Top down –suggests what should be there • Bottom up – signals what is there

5. Depth perception • Eberts and MacMillan (1985) showed higher than average rate that small cars are hit from behind • Because of the cue of relative size difference • Features of the world violate our expectations, but top-down processing takes over and gives inappropriate perception.

5. Depth perception • Eberts and MacMillan (1985) showed higher than average rate that small cars are hit from behind • Because of the cue of relative size difference • Features of the world violate our expectations, but top-down processing takes over and gives inappropriate perception. • Clever design application • Drivers overspeeding while approaching traffic circle • Denton (1980) drew lines of ‘diminishing separation’ on the road to give the driver the increasing flow of texture past the driver (signaling an increase in speed) – top down. • Driver should instinctively slow to the safe speed.

6. Conclusions • We have limitations in our visual system • There are top down influences • And Bottom up • Understanding of perception & system goals can help

6. Conclusions on visual sensory systems • Our limitations of our visual system • Influence the information input and hence our perception • Some top down influences include • Expectancy and learning • Some bottom up • Planned signals

6. Conclusions on visual sensory systems • Our limitations of our visual system • Influence the information input and hence our perception • Some top down influences include • Expectancy and learning • Some bottom up • Planned signals • Information about perception • and understanding of the system goals and attributes • can be used to help guide the design of the display

Partial overview of other sensory systems • 1. An example of a workplace error & noise • 2. Sound, an auditory stimulus • 3. Alarms • See also ch.5 in Wickens text

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.”

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

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

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.

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.

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

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.”

IE 486 Work Analysis & Design II