Getting to grips with Fatigue & Alertness Management(56)

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Performance in trials demanding sustained attention improves during the morning to reach a maximum in the middle of the afternoon then starts to decline towards the evening to reach a minimum during the night.
 
Degradation in performance is sometimes observed early in the afternoon. This phenomenon, called the "post lunch dip" effect, occurs even when meals are not eaten.
 
Circadian variations in efficiency are, in most cases, highly correlated with variations in body temperature except in the early afternoon where this is paradoxically not paralleled by a similar decrease in temperature.
 

 
 
 
 
6.4.3.2. MODULATION OF CIRCADIAN VARIATIONS

Exerting a greater effort can compensate for circadian rhythmicity: the reduction in performance controlled by circadian rhythmicity can be compensated for if the operator is able to mobilize more of his resources.
The ability for mobilizing resources varies according to:
. the type of task,

. the individual

. motivation,

. learning,

. knowledge of performance results.

Increasing the mobilization of the operator's capabilities, operational adaptation, change from a low activity state to an active mobilization state, when foreseeable or random events occur, causes physiological problems and has long-term medical consequences for the operator.
 

 
 
 
 
 
 
 
 
 
 
6.4.4. SLEEP LOSS & PERFORMANCE

6.4.4.1. DEFINITION

Partial sleep loss can be either attributed to a reduction in sleep time amounting to several hours (going to bed late, getting up early) or to a fragmentation of the sleep period.
 
Deterioration in performance related to sleep loss is generally indicated by omissions in test or in supervisory monitoring processes, i.e. periods of non-response to a critical signal. These periods correspond to episodes of drowsiness or reduced alertness levels.
 
Monotonous supervisory tasks are those that are the most affected by sleep loss. They present a low sensorial stimulation level, constant or repetitive, but requiring constant alertness.
 
6.4.4.2. MANISFESTATIONS

Signal detection: the capability to detect rare and low-level signals drops as sleep debt increases.
 
Rational critical analysis of situations: individuals with a sleep debt will have a tendency to accept raw sensorial impressions without critical analysis. During situations favoring the appearance of sensory illusions, or even visual and auditive hallucinations, a subject, even well-trained, will loose all ability to rationally criticize a situation and will act in an inappropriate manner. Sleep debt reduces the possibilities for critical analyses of increased sensory impressions.
　
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