Polygraph machines and their recent software-based incarnations measure pulse, perspiration, vocal frequency and pupil dilation in order to reveal whether someone is telling the truth or not. In short, when we lie we get a little flustered. By remembering the “base rate” benchmark of the individual, the software estimates whether the subject experiences stress during a particular line of questioning. They are fallible purely because they are designed to detect subtle signs of stress – not the deception itself. Continue reading →