The effect of split sleep schedules (6h-on/6h-off) on neurobehavioural performance, sleep and sleepiness Michelle A. Short a, b, c, * , Stephanie Centofanti a , Cassie Hilditch a , Siobhan Banks a , Kurt Lushington a , Jillian Dorrian a a Centre for Sleep Research, University of South Australia, Adelaide, Australia b Bushfire Cooperative Research Centre, East Melbourne, Australia c School of Psychology, Flinders University, Bedford Park, Australia article info Article history: Received 27 October 2014 Received in revised form 20 October 2015 Accepted 9 December 2015 Available online Keywords: Split sleep Shiftwork Sustained operations Continuous operations Attention Performance abstract Shorter, more frequent rosters, such as 6h-on/6h-off split shifts, may offer promise to sleep, subjective sleepiness and performance by limiting shift length and by offering opportunities for all workers to obtain some sleep across the biological night. However, there exists a paucity of studies that have examined these shifts using objective measures of sleep and performance. The present study examined neurobehavioural performance, sleepiness and sleep during 6h-on/6h-off split sleep schedules. Sixteen healthy adults (6 males, 26.13y ± 4.46) participated in a 9-day laboratory study that included two baseline nights (BL, 10h time in bed (TIB), 2200h-0800h), 4 days on one of two types of 6h-on/6h-off split sleep schedules with 5h TIB during each ‘off’ period (6h early: TIB 0300h-0800h and 1500h-20000h, or 6-h late: TIB 0900h-1400h and 2100h-0200h), and two recovery nights (10h TIB per night, 2200h- 0800h). Participants received 10h TIB per 24h in total across both shift schedules. A neurobehavioural test bout was completed every 2 h during wake, which included the Psychomotor Vigilance Task (PVT) and the Karolinska Sleepiness Scale (KSS). Linear mixed effects models were used to assess the effect of day (BL, shift days 1e4), schedule (6h early, 6h late) and trial (numbers 1e6) on PVT lapses (oper- ationalised as the number of reaction times >500 ms), PVT total lapse time, PVT fastest 10% of reaction times and KSS. Analyses were also conducted examining the effect of day and schedule on sleep vari- ables. Overall, PVT lapses and total lapse time did not differ significantly between baseline and shift days, however, peak response speeds were significantly slower on the first shift day when compared to baseline, but only for those in the 6h-late condition. Circadian variations were apparent in performance outcomes, with individuals in the 6h-late condition demonstrated significantly more and longer lapses and slower peak reaction times at the end of their night shift (0730h) than at any other time during their shifts. In the 6h-early condition, only response speed significantly differed across trials, with slower response speeds occurring at trial 1 (0930h) than in trials 3 (1330h) or 4 (2130h). While subjective sleepiness was higher on shift days than at baseline, sleepiness did not accumulate across days. Total sleep was reduced across split sleep schedules compared to baseline. Overall, these results show that while there was not a cumulative cost to performance across days of splitting sleep, participants obtained less sleep and reported lowered alertness on shift days. Tests near the circadian nadir showed higher sleepiness and increased performance deficits. While this schedule did not produce cumulative impairment, the performance deficits witnessed during the biological night are still of operational concern for industry and workers alike. Crown Copyright © 2015 Published by Elsevier Ltd. All rights reserved. 1. Introduction Shift work is problematic because it frequently entails both prolonged wakefulness and circadian misalignment (Folkard et al., 2005). Resultantly, shift work is associated with impaired alertness and heightened risk of fatigue, workplace accidents, performance * Corresponding author. Centre for Sleep Research, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia. E-mail address: michelle.short@unisa.edu.au (M.A. Short). Contents lists available at ScienceDirect Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo http://dx.doi.org/10.1016/j.apergo.2015.12.004 0003-6870/Crown Copyright © 2015 Published by Elsevier Ltd. All rights reserved. Applied Ergonomics 54 (2016) 72e82