Abstract
It is suggested that crew members of future armoured vehicles will be reclined. However, information relating to task performance when reclined for prolonged (i.e. >30 minutes) periods is limited. This study has investigated the effects of prolonged reclining on a simple target detection task.
Twelve subjects undertook four separate seventy minute studies in the upright (control) seated posture or reclined, with head support, at 25°, 45°, and 65° from the vertical. Subjects viewed a model scrubland scene, with light emitting diodes hidden behind the scrub, through seven vision blocks which covered a 300° field of view. During the first 10 minutes subjects responded to a sequence of 32 randomly distributed signals of 4 seconds length, with 15 seconds between each signal. They rested for 50 minutes before repeating the 10 minute test epoch. Measurements taken were number of responses, body part discomfort, sleepiness and Stress and Arousal Checklist, and were analysed using Analysis of Variance.
Percentage targets detected significantly reduced with back angle, with the greatest reduction being in the subjects' frontal arc. General body and neck discomfort and sleepiness significantly increased with back angle. Reported stress significantly increased and arousal decreased, but only between 0° and 65°. There was no significant time effect.
Possible explanations for the results are that the chair and posture inhibited freedom and ease of movement, or that increased discomfort at the more acute angles may have resulted in an altered searching behaviour. Whatever the mechanism this study has shown that reclined postures may significantly impair the performance of an all-round surveillance task, particularly at the more acute back angles.
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