Sweat, Lies and Heart-rates

Grass 7D Polygraph machine 2008/184/1. Collection, Powerhouse Museum
Grass 7D Polygraph machine 2008/184/1. Collection, Powerhouse Museum

One of the coolest objects I have acquired for the Health and Medicine collection is the Grass 7D polygraph machine.

A common deus ex machina devise for Hollywood script writers – Polygraph machines, or ‘lie detectors’ are one of those objects that are so embedded in the public consciousness by popular culture that to see an actual example ignites curiosity. Upon seeing it though, one realises that it is the drama surrounding the need for the polygraph that is captivating – not so much the machine itself! Nevertheless, this is an impressive looking piece of scientific equipment, and one’s curiosity immediately switches to ‘how does it work then?’

The polygraph works by recording skin conductance response, evoked cardiac response, reaction times, respiratory response, and orienting response. That is, it measures and records your sweat, pulse rate, breathing, and how much you stammer and think about your answers. These can be very subtle variances though, and the machine and its highly practised operator can read these.

The High Court of Australia is still yet to decide on the use polygraphs as substantial evidence, though it is doubtful they will ever be held admissible in Australian criminal courts. Regardless, there are private companies in Australia providing a polygraph service for use in lie detection. Australian tabloid style current affairs television shows often engage the services of such companies, and there is even a North American ‘reality games show’ television production, ‘Moment of Truth’, that uses the polygraph as the crux of its entertainment.

As important as catching cheating partners, lying criminals, and entertaining the masses are, this particular polygraph was used by researchers at the Psychology department of the Macquarie University in Sydney. And although this machine is yet to make an appearance on the big or small screen, it has featured in medical journals!

Damian McDonald

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