Circadian rhythm and chronic sleep deprivation effects on human performance - eye-tracking experiment.

Twenty four paid volunteers participated in this experiment (12 females, mean age 22.7 ± 1.6 years). Participants met the experiment requirements: right-handedness, right-eyed, normal or corrected-to-normal vision, no physical or psychiatric disorders. They were all non-smokers and drug-free.
The experimental task was performed in two conditions: rested wakefulness (RW – after a week with unrestricted, fully restorative sleep) and chronic sleep deficit (SD, after seven days of sleep curtailment by 30%). The order of experimental sessions (RW and SD) was counterbalanced across all participants. The sessions were separated by at least two weeks in order to minimize the residual effects of sleep deficit on performance.
All the participants performed an experimental task four times during the day: at approximately 10:00, 14:00, 18:00 and 22:00. A semi constant routine protocol was applied: room temperature and light intensity were kept constant, caloric intake and the level of motor activity were controlled. The participants spent approximately 14 hours in a controlled laboratory environment. During experimental days, they were allowed to engage in non-strenuous activities (eg. reading, watching videos, conversation). Caffeine intake was banned; alcohol consumption during the preceding week was restricted.
A modified spatial cueing task (Posner, 1980) was prepared using E-Prime 2.0 (©Psychology Software Tools) and presented on a 17-inch screen located approximately 80cm from participants' eyes. Targets and cues were presented in six possible locations at 8° and 2° of visual angle in x-axis and 5° and 1° in y-axis of visual angle respectively. Leftwards and rightwards target locations were distributed equally, whereas middle target locations were weighted by 50% vs. 25% of upper and 25% of lower locations. The task comprised congruent trials with target stimuli preceded by congruent directional cues (60%), incongruent trials with target stimuli preceded by incongruent directional cues (15%), and stimuli without cues (25%). The total number of stimuli in the task was 500 in each measurement. Targets were presented for 500ms and cues for 200ms. The intertrial interval was varied in the range of 800 - 3500ms with average of 2200ms. Time interval between cue and target varied between 200 and 700ms with an average of 450ms. The participants were instructed to direct their attention and gaze from fixation point to targets only if they were preceded by a cue. The task lasted about 35 minutes. One week prior to the first experimental day, participants were extensively trained on the experimental task, in order to avoid the influence of a learning process on the number of errors.
Eye position was monitored with Smart Eye Pro (Smart Eye AB, Göteborg, Sweden).

Posner, M. I. Orienting of attention. Q. J. Exp. Psychol., 1980, 32: 3-25.

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