Seeing the latest Blade Runner film recently has reminded me of the significance of pupil response as an indicator of health, both mental and physical.
You may remember the scene in the original film, revisited in the new film, where the definitive test in identifying an android from a human is the Voight-Kampff machine, a fictional interrogation tool. As Tyrell himself states, the machine detects anomalies in ‘Capillary dilation of the so-called blush response? Fluctuation of the pupil? Involuntary dilation of the iris?’ when the subject is asked a series of increasingly emotive questions.
Pupil responses are complex. As well as the light reflexes and the link with accommodation, there are higher centre inputs, such as that causing miosis during sleep, a psychosensory reflex causing dilation when emotionally aroused (with input from the amygdala), a vestibular-influenced mydriasis linked with balance, a miosis linked with activity of the orbicularis muscle, and a dilation followed by constriction caused by trigeminal nerve activity.
Much as Philip K Dick’s predictions of loss of individual thought (he as good as predicted the US Prism program) and of the increasing homogenisation of living and artificial lifeforms should be both celebrated and taken heed of, efforts to enforce autonomic responses as legal evidence have always fallen at the first hurdle. Any pathway with both objective and subjective influence will always show too great a variation to be anything other than a sometimes useful but easily fooled indicator.
In the UK, pupil dilation has been tested as an indicator of intoxication of suspected drug users. In the US, a pupil testing kit was available to check drivers suspected of being under the influence. Some interrogation practices have tried pupil responses. Undoubtedly, a relative difference between the eyes could have found evidence of underlying disease, but individual emotional response and metabolism will always leave these tests for human identification in the realms of sci-fi.