This is a checklist to go through when setting up a participant.
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Is the participant wearing spectacles? Check if they are clean. Don’t attempt to clean spectacles using a handkerchief, tissue or paper towel. It will just spread out the grease as a thin film. Use dish soap or an eyeglass cleaning solution. Assure your cleaning solution is safe to apply to the glasses. Dry with a lint free cloth.
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Use a stable chair that cannot be easily moved by the participant. A barber chair that can be raised and lowered, and moved back and forth by the experimenter while the participant is sitting in it is ideal. If possible use a head/neck rest.
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Make sure the participant’s face is (roughly) at the appropriate subject distance from the eye-tracker.
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If you use a forehead marker, place it above the nose on the participant’s forehead. See image below.
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Check if the face is horizontally centered in the thumbnail image shown by eyevec-control. The participant should be positioned so the eyes and (partially) the forehead are visible.
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For children or infants you might need to change the eye-tracker to a lower position, since their faces will be closer to the desk. If so, be sure to the adjust the related settings Eye-tracker stand and Eye height from desk.
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When collecting data for accuracy measurements or for any research that requires working with correct visual angles check if the height from the eyes to the desk matches the setting given in Eye height from desk and adapt if necessary or raise/lower the participant.
Forehead marker placement
Using a forehead marker is optional, so the following is only revelant if you actually are using one.
If possible place the forehead marker above the nose between the eyebrows or just above. In case of spectacles make sure the spectacle bridge does not obscure the marker in the camera image.
For participants with a pronounced brow ridge as in the image[1] shown you might try sticking only the lower part of the marker to the face, so the marker stays reasonably flat. Note, this will only work if the marker doesn’t curl up, which might happen if you are reusing a marker.
