Stress & Workload Chapter 13

1. Stress & WorkloadChapter 13 Rebecca W. Boren, Ph.D. IEE 437/547 Introduction to Human Factors Engineering Arizona State University December 5, 2011

2. What are stressors? Textbook: Influences on information availability and processing that are not inherent in the content of the information itself.

3. What are stressors? Textbook: Influences on information availability and processing that are not inherent in the content of the information itself. Dictionary: An agent, condition, or other stimulus that causes stress to an organism.

4. What are stressors? Textbook: Influences on information availability and processing that are not inherent in the content of the information itself. Dictionary: An agent, condition, or other stimulus that causes stress to an organism. Something that causes physical, mental, or emotional strain or tension.

5. Examples of physical stressors: noise, vibration, heat or cold, dim lighting.

6. Examples of psychological stressors: anxiety, fatigue, frustration, and anger

7. The Effects of Stress • A psychological experience: usually, but not always feelings of frustration or arousal.

8. The Effects of Stress • A change in physiology: e.g., change in heart rate or a change in the output of catecholamine, measured in the urine after periods for flying combat maneuvers.

9. The Effects of Stress • Stressors affect the efficiency of information processing, usually, but not always degrading performance. • Stressors may have long-term negative consequences for health.

10. The Effects of Stress • Headache • Sleep disturbances • Difficulty in concentrating • Short temper • Upset stomach • Job dissatisfaction • Low morale

11. Environmental Stressors -Motion • High frequency motion: cyclic motion (aka vibration) – can be specific to a part of the body (handheld power saw) or to the whole body.

12. Environmental Stressors -Motion • Low frequency motion (rocking of a ship) and motion sickness: acts as a distracter making it hard to concentrate.

13. Environmental Stressors -Motion • Whole body vibration makes it difficult for the user to input or control the device because of loss of precision. Written information may be blurred.

14. Dim Lighting Noise Environmental Stressors, cont’d

15. Remediation for Environmental Stressors • Remediation involves using the midrange of lighting and sound. • Remediation for hand vibration involves tool selection and limiting dose exposure. • Remediation for whole body vibration involves insulating the user and the interface (input device) from the source of vibration (cushioning).

16. Thermal Stress • Excessive heat or cold degrades performance and causes health problems. • Comfort zone: 73oF to 79oF in the summer; 69oF to 75oF in the winter. • Humidity: less humidity is allowed (60%) at the upper temperature limit; more is allowed (85%) at the lower limit.

17. Thermal Stress • Sources of excessive heat: furnaces or boilers, outside temperatures, ovens, etc. • Sources of excessive cold: freezers, outside temperatures, air conditioning

18. Remediation for Thermal Stress • Body temperature is moderated by • Clothing (may cause a loss of manual dexterity) • Air movement • Physical activity • Provide ample amounts of fluids in excessive heat.

19. Poor Air Quality • Poor ventilation – may not even be aware of carbon monoxide • Pollution or smog • Lack of oxygen (anoxia) at high altitudes and cold can lead to frostbite as the body tries to provide oxygen to the brain and heart. • Negative effects on perceptual, motor, and cognitive performance

20. Psychological Stressors Perceived threat of harm or loss of esteem (embarrassment), or something valued, or of bodily function through injury or death.

21. Psychological Stressors • Varies by individual (thrill-seeker versus the novice) • Amount of stress is related to the persons understanding or cognitive appraisal of the situation. • Varies by person depending on their sense of control. May not appreciate the danger. • Research difficult in this area because of ethical issues.

22. Level of Physiological Arousal Related to Stress • Documented by changes in • heart rate • pupil diameter • hormonal chemistry

24. Optimal Level of Arousal • Performance increases as arousal increases up to a certain point (trying harder). • Performance decreases with overarousal (overload).

26. Performance Degradation with Overarousal. • Perceptual or attentional narrowing (tunneling) • May cause you to focus on the wrong thing. • Less ability to use working memory to come up with creative solutions. • Long-term memory intact.

27. Example: Three Mile Island disaster caused by the stress of the auditory alarm indicating a problem when none existed. The stress may have caused the workers to overlook a wider range of correct indicators.

28. Remediation of Psychological Stress During an Emergency • Have written instructions (do not rely on working memory)

29. Remediation of Psychological Stress During an Emergency • Practice for emergencies (overlearn). We tend to perform the dominant behavior (turning back from a skid on slippery ice because that’s what we do on dry pavement)

30. Remediation of Psychological Stress During an Emergency • Avoid the tendency to “do something now.” • Take time to take a deep breath and plan a strategy.

31. Life Stress • Stress related to the job or personal life. • Poor performance because of lack of attention or motivation. • Safety may be compromised because of distraction or diversion of attention.

32. Remediation is complex. Here are some general suggestions: • Address and remove the source of stress within the organization (i.e., low pay, long working hours, etc.) • Stress management training • Provide counseling

33. Human Factors study of Workload Human Factors Rap Video Produced by graduate students in Dr. Warm’s laboratory.

34. Workload • The amount of work assigned to or expected from a worker in a specified time period. • Stress may be induced by having too much to do in too little time. • Overload can result in forgetting to do some critical task e.g., air traffic controller forgetting that he had already scheduled another aircraft to land on the runway.

35. Measuring Workload • TR/TA (time required for the task/time available for the task) or time-ratio • Determined by task analysis (include “think time”) • Allow for spare capacity of about 20% • Ideal ratio is 0.8 • Ratio can be > 1.0 if time-sharing

37. Consequences of Work Overload • More selectivity of input • More important sources of information given more weight • Decrease in accuracy • Decreasing use of mental strategies that require heavy mental computation. • Locking onto a single strategy.

38. Remediation • Task redesign or assignment to multiple workers • Automate • Develop display design that highlights the most important information. • Training for high time-stress workload situations. • Training of task management skills

39. Laying out a timeline of what needs to be done and how long it will take. • Identification of task times • Scheduling and prioritization • Task resource demands and automaticity • Multiple resources

40. Mental Workload Measures (1) • Primary task measures

41. Mental Workload Measures (2) • Secondary task methods • Measure the reserve capacity left over after performing the primary task (examples: memory tasks, mental arithmetic)

42. Mental Workload Measures (3) • Physiological measures • Heart rate • Blink rate • EEG • Pupil diameter

43. Mental Workload Measures (4) • Subjective measures • Example: NASA Task Load Index (TLX) • Ask the workers.

44. Fatigue • One effect of continuous work overload is fatigue. • Fatigue is a stressor that degrades performance and creates problems in maintaining attention.

45. Fatigue • Fatigue studied in military operations (Desert Storm), long-haul truck drivers, medical workers in hospitals. • Fatigue can also result from long periods of doing little.

46. Vigilance and Underarousal • An increased number of misses as the vigil progresses (quality control inspectors)

47. Vigilance and Underarousal • Factors that lead to loss of performance • Time • Event salience (Is event very noticeable?) • Signal rate • Arousal level

48. Vigilance and Underarousal • Automation may make the problem of underarousal worse.

49. Vigilance remediations • Watches should not be too long. • Operators should get frequent rest breaks. • Signal could be enhanced or increase the payoff for detecting the signal. • Introduce false alarms to “keep them on their toes”. • Appropriate use of stimulants: caffeine (infrequently), music, conversation (if not distracting).

50. Sleep Disruption • Sleep deprivation (getting less than 7 to 9 hours per night) • Being out of sync with our natural circadian rhythms (e.g., early morning work) • Disruption of circadian rhythms through jet lag or shift work.