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Saving calibration results (for re-usage)

Hi everyone,

I was wondering if there is a way to save (or reuse) calibration (or the last calibration) results, so that if I do two experiments with the same subject, I do not need to re-do the calibration but just to validate it. Is it a good way to do eyetracking?

Have a good day,

Hi, in general, no, you should always re-do calibration before every session (and even within a session when required). Things change across sessions (position and angles of the subject relative to the camera, wearing contacts vs glasses, lighting conditions, and so on). Also going though a calibration procedure before each session ensures that you pick up issues that you might not otherwise detect. e.g. what if your participant is wearing mascara on the second session, and at certain gaze angles, that causes a misidentification of the pupil? Better to detect that while you are calibrating rather than wonder after the experiment was run why the gaze data looks so strange.

But firmer recommendations really need to based on the particular eye tracker you are using.

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Dear Michael,
thanks for your comment. It actually makes sense. What I mean in-between sessions is that the sessions occur one after another with a short break of a minute or so. (I plan to use EyeLink 1000 with a chin rest and forehead support). But here, I guess it is still better to re-calibrate as the position of the person might still change during the break.

The best strategy here is to calibrate at the beginning of the session (using the normal idea of an experimental session, referring to the overall visit for the day), and then then check the validity of the calibration between trials (i.e. with multiple trials making up your session).

Only actually re-calibrate if the calibration no longer appears to be valid. Calibrating too often can itself lead to problems: only re-do it if it is actually necessary.

Ideally record the calibration checks so you have an objective record of the calibration quality throughout the session (e.g. before each trial, show some stimuli at a succession of known locations and have the subject fixate each in true). This means that each trial of recorded data has an associated record of the calibration quality.