FOOD STIMULI AND GENDER

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3.2 Data collection
The experiment was conducted in a laboratory setting at Hohenheim University in
the Department of Nutrition Psychology and lasted approximately 30 minutes for each
participant.
3.2.1 Eye Tracking
Tobii Pro Glasses 2 were used to capture subjects’ eye movements and fixation
points. Tobii Pro Glasses 2 are a wireless eye tracker device with a live view software
function. The eye tracker has four cameras, two for each eye. A gaze sampling of 50 Hz was
utilized; this is a sampling interval of 20 ms. This particular eye tracker uses pupil corneal
reflection technology, which creates a reflection of light on the cornea. The eye moves, but
the reflection remains stationary, and eye movements can be recorded. For this purpose,
Tobii Pro Glasses 2 have a set of illuminators that project infrared light and create
reflections. This eye tracker can choose between bright pupil (pupil appears brighter than
the iris) and dark pupil (pupil appears black or darker than the iris) tracking; depending on
the position of the light source one or the other is used (Holmqvist et al., 2011; Tobii AB
Technology, 2015).
A calibration of each participant is required, since the fovea in not in the same
position in every person and is not necessarily at the center. A one-point calibration and
three-point validation were performed on each participant before starting each recording
using the calibration card and instructions provided by Tobii AB Technology (Holmqvist et
al., 2011; Tobii AB Technology, 2015). Through the three-point validation of the
calibration, a maximum of 1.2 grade accuracy error was admitted, which was adequate for
this experiment due to the large size of the areas of interest.