2.4.1. Eye blink rate
As spontaneous EBR remains steady during the day but increases in the
evening (at about 20:30, see Barbato et al., 2000), no EBR was recorded
after 18:00. Participants were also urged not to smoke before their
arrival. Throughout the experiment, the spontaneous EBR was measured
three times for each participant. At the start of each Ocular task, a
nine-point eye-movement calibration was performed, which was followed by
a light gray screen with a central fixation cross for 3 min.
Participants were sat comfortably alone in the room and asked not to
gaze, but just to look casually at the fixation cross in a relaxed
state. The individual EBR (blinks/min) was calculated by dividing the
total number of eye blinks during the 3 min measurement interval by the
duration (in minutes). Eye blinks were marked by the Eyelink online
event parser using a proprietary algorithm based on several consecutive
missing pupil samples, which was independently demonstrated to identify
blinks accurately (Ehinger et al., 2019). The blinks that were outside
of the normal range of blink duration were removed to assure data
quality in blink measurements (less than 80 ms or more than 900 ms, as
reported by Ehinger et al., 2019).