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April 2012 www.sname.org/sname/mt and they ranged from diary keeping to the use of electrodes to record brain activity. e following four primary methods were used during the week. Diaries . Each participant had to ll in a set of diaries and a number of questionnaires before, during, and after the experiments. Diaries were kept to record the levels of sleepiness, as measured on the Karolinska Sleepiness Scale (KSS), and stress. e KSS scale ranges from 1 (extremely alert) to 9 (extreme tiredness). This was recorded every hour on watch, and on the hour o watch, if the participant was still awake. At the end of the watch, participants were also asked to record their food intake on watch, how well they thought they had performed, and their perceptions of the workload. A wake diary also enabled participants to record other activity while off watch, snacks taken, and the type of activity done during free time. Participants were allowed to use the academys gymnasium but only under controlled conditions up to one hour immediately after watch each day. A sleep diary was completed upon wak- ing after each period of rest and focused on the quality of sleep in the last o watch period. Data was sought on how quickly participants fell asleep, how often they woke, diculties experienced in sleeping, and how refreshed they felt upon waking. Actiwatches. e Actiwatch is both a brand name and a common general term used for small, portable activity measurement devices worn on the wrist (or leg) to measure acceler- ation, and thus calculate physical activity and sleep duration. Each participant wore these on his or her non-dominant arm throughout the week. e Actiwatch measured accelera- tion, so the movement of participants could be recorded and thus provide information on the periods of wakefulness and sleep during the o -watch period. Computer-Based Measures . Two computer- based measurements were taken, called the PVT test, and the Stroop test. PVT stands for the psychomotor vigilance task, a test that is sensitive to fatigue. e PVT was performed on portable devices, always before starting a simulator watch, and once on completion of a watch. is means 28 test results were recorded for every participant by the end of the run. Once initialized, the PVT test pres- ents a target to the participant on a small screen at random intervals, and the partici- pant has to press a button to record when the target is seen. Each test lasted approximately ve minutes, and the reaction time, the num- ber of lapses, the mean reaction time, etc., were all recorded and stored on the device. At the end of each watch, and after com- pleting the PVT test, the participants carried out a Stroop test on a laptop located in the same area as the PVT. As with the PVT test, this task was undertaken while the partici- pant was alone in the room, to enable total concentration. The names of two differ- ent colors (green and red) appeared on the screen and the participants had to click the color name as quickly as possible, ignoring Attaching electroencephalogram (EEG) electrodes. Participants wore these for a 24-hour period, through two watches and two rest periods. PHOTO BY BRANIMIR PANTALEEV. A member of the Horizon team working in the engine room simulator. PHOTO BY PAUL WATTS. e voyage was constructed to mimic a real voyage in the English Channel.