Interaction of Task Amplitude with Circadian Variation in Auditory Vigilance Performance

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Abstract
Two groups of human Ss [subjects] performed 2 1 h auditory vigilance tasks at 08.00 h and 20.00 h. The task comprised a taped sequence of tone bursts of 610 Hz for durations of 0.5 or 0.4 s in a background of low frequency noise on a single loudspeaker. The tones were 5dB above the noise in all conditions. The shorter tones were defined as signals and occurred randomly at an average rate of 40/h. For 1 group the noise level at the ear was 70 dB; for the other group the level was 90 dB. Detection rate improved from morning to evening for the low noise group but not for the high noise condition. Also vigilance decrement was reduced in the evening. An arousal explanation was supported.