Demystifying this concept: The mechanism is almost certainly just measuring pupil dilation, and maybe eye focus, if that's something you can track with an eye f

Demystifying this concept: The mechanism is almost certainly just measuring pupil dilation, and maybe eye focus, if that's something you can track with an eye facing camera. Source: Thinking Fast and Slow, where the initial inspiration for the book was an experiment noting that human's pupils reflexively dilate when they engage their "system two," aka the "slow brain," metaphorical part of their mind.