Hysteria, or conversion disorder as it is now known, is when neurological symptoms such as blindness or paralysis are present but no neurological problems or brain abnormalities can be found.
The issue of whether such patients are ‘faking’, whether the neurological abnormality just hasn’t been found yet, or whether the problem is best understood in psychological terms, has been vexing clinicians for the best part of 200 years.
This is a fascinating quote from the introduction to Contemporary Approaches to Study of Hysteria (ISBN 019263254X) by Halligan, Bass and Marshall:
…how can we discover if someone is indeed faking it? (We use ordinary language here rather than the more obviously psychiatric terms such as factitious disorder and malingering: clarity and logic are best served by calling a spade a spade.) The simple but totally impractical solution would be 24-hour surveillance on audio- and video-tape unbeknownst to the patient. Anyone who behaved perfectly normally when alone but who invariably developed the ‘disability’ when in company might be plausibly thought to be feigning.
Short of this Big Brother solution, investigators have tried to devise catch-trials and catch-tests to detect the cheater. For example, it is sometimes assumed that a patient who ‘guesses’ a randomized stimulus sequence (touch, touch, no touch…) significantly below chance must be faking it.
But the existence of such phenomena such as blindsight, unfeeling touch, unconscious perception in visual-spatial neglect and priming in amnesia show how misleading it can be to assume that odd relationships between behaviour and verbal report necessarily constitute evidence of cheating.
We do not impinge on the honesty of patients who perform visual discriminations at above chance level while claiming to have seen nothing. Why should we perforce distrust those who score below chance? In short, the detection of lying in the neurology clinic is at least as difficult as it is in a court of law.