Lapses in performance have been described also among air traffic controllers (Folkard & Condon, 1987) concerning the so-called "night-shift paralysis," such as a sudden immobility of the voluntary muscles during consciousness, which can last from a few seconds to a few minutes, occurring in about 6 percent of the subjects with peaks around 5 a.m.; it seems related to the number of successive night shifts worked and sleep deprivation.
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These are important aspects to consider, particularly when high and sustained levels of performance efficiency are required as public health is at stake, and its failure may be very costly both from the social and economic point of view; such is the case with aviation activities. Besides, new technologies, which increase cognitive tasks and require more alertness and vigilance, are often more vulnerable to errors than manual work activities. On the other hand, automated systems may increase monotony and boredom, thus decreasing vigilance and safety, particularly in case of emergency. It is worth mentioning that both the two main nuclear-reactor accidents at Three Mile Island (1979) and Chernobyl (1986) and the Bhopal chemical plant disaster (1984) started during the night hours (at 0400, 0125, and 0057 hr, respectively), and in all situations "human error" has been claimed as an important factor. Besides, Kelly and Schneider (1982) assessed the risk of accident in a nuclear power plant working on 12-hr shifts to be 70 percent higher than on 8-hr shifts.
Stressors can affect social awareness in a number of different ways, including attentional narrowing, reductions in information intake, and reductions in working memory capacity. Under stress a decrease in attention has been observed for peripheral information, those aspects that attract less attentional focus, and there is an increased tendency to sample dominant or probable sources of information. This is a critical problem for social awareness, leading to the neglect of certain elements in favor of others. In many cases, such as in emergency conditions, it is those factors outside the person's perceived central task that prove to be lethal. In aviation, many lives are lost due to controlled flight into the terrain accidents, with attentional narrowing serving as a primary culprit. Premature closure, arriving at a decision without exploring all information available, has also been found to be more likely under stress. This includes considering less information and attending more to negative information. Recent research has also found that scanning of information under stress is scattered and poorly organized. A lowering of attention capacity, attentional narrowing, disruptions of scan patterns, and premature closure may all negatively effect social awareness under various forms of stress.
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On long-hour shifts, the periods of decrement in vigilance of air traffic controllers are more likely to occur during the monotonous shift, and occur more frequently during night than day shifts. Reviewing some of the main airline accidents that occurred in the period 1967-1988, Price and Holley (1990) underlined that chronic fatigue, sleep loss, and desynchronosis were three "human factors" that contributed significantly to the unfavorable events. In most cases they were the consequence of improper work scheduling, which imposed prolonged duty periods and irregular wake times in the previous hours, not allowing sufficient time to rest and sleep. In other cases the influence of circadian desynchronization due to time-zone changes or to night work (in one case concerning maintenance personnel) appeared evident. The negative effect of sleep loss and shift work on mental performance has been claimed also for the Space Shuttle Challenger accident.
References
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Andlauer P., Rutenfranz J., Kogi K., Thierry H., Vieux N., & Duverneuil G. (1982). "Organization of night shifts in industries where public safety is at stake". International Archives of Occupational and Environmental Health, 49, 353-355.
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Costa G. (1993). "Evaluation of work load in air traffic controllers". Ergonomics, 36, 1111-1120.
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