1 Instructor: Vincent Duffy, Ph.D. Associate Professor Lecture 4 – Perception: Other Senses & Information Processing Tues. Jan. 30, 2007 IE 486 Work Analysis & Design II

2 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?

3 An overview – 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 4. The trouble with sound transmission 4. The trouble with sound transmission 5. Noise revisited 5. Noise revisited 6. Noise remediation 6. Noise remediation 7. Other senses: touch and vestibular 7. Other senses: touch and vestibular 8. Conclusions 8. Conclusions

4 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.”

5 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

6 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

7 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.

8 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 dB is a point at which potential danger to the ear can occur.

9 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

10 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.”

11 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

12 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.

13 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

14 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’.

15 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.

16 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

17 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

18 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.

19 Information processing model (p.122)

20 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