Eye tracking is a technology that can track where someone is looking.
More specifically, it tracks where the foveal or central gaze is.
Eye-tracking data can be misleading.
Reason 1. It tells yo what people looked at, but that doesn't mean they paid attention to it.
Reason 2. Eye-tracking only measures central vision.
Reason 3. It's easy to accidentally skew the eye-tracking dat depending on what instructions you give them before and during the eye tracking study.