The Effect of Repetition of Relevant and Irrelevant Tasks over Day and Night Work Periods

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Abstract
The effects of repetition on the Wilkinson Vigilance Task and an unobtrusive performance measure (crossword completion) were examined in 18 subjects over two 8 h work periods. Vigilance trials alternated with breaks in 25min segments across a work period from 0900 to 1700 h and a period from 2400 to 0800 h. Performance decrements were seen in hit rate and on the irrelevant task measure across the night session, and in hit rate across the day session. Decrements were greater at night than during the day on both measures. The number of attempts on the vigilance task decreased across trials similarly in both testing sessions. It was concluded that specific task repetition results in performance decrements, even when circadian incremental effects would be predicted, and that the placement of such task repetition at night magnifies those decrements and extends them to intrinscially as well as extrinsically motivated tasks.