2. 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

3. Administrative Lectures 1 & 2 available on course webpage : //web.ics.purdue.edu/~duffy/index486 1 st 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

4. 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)

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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!

11. 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)

12. 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

13. 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).

14. 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

15. 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

16. 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

17. 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.

18. 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.

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

20. 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

21. 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

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

23. 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.”

24. 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

25. 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

26. 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.

27. 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.

28. 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

29. 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.”