In general, a witness at trial may only testify as to what he or she has personally seen or heard.
Obviously, sometimes it is necessary for one or both sides at trial to present evidence that goes beyond that sort of direct testimony. If the prosecution wishes, for example, to explain to a jury what conclusions may be drawn from the fact that blood splattered in a certain pattern, they must offer up a witness who will not only testify about the blood splatter he saw, but also offer an opinion about what conclusions can reasonably be drawn from that splatter pattern.
Such a witness is called an “expert witness.” When a witness is qualified as an expert, he may present his own opinions on the meaning of facts within his area of expertise.
A psychic’s testimony at trial could theoretically be accepted under one of two theories. First, the psychic ability could be considered as analogous to sight or hearing, and the psychic would testify only as to what he or she saw/heard/experienced. This would assume (of course) that there was general, wide consensus as to the existence of psychic powers, AND that the way the powers worked was by conveying an accurate reproduction of a real event, like a film or tape recording.
But most fictional accounts don’t depict psychic powers that way. There’s often a measure of interpretation that must be applied to the “vision” or “experience”. For example, in one episode of “Medium,” Allison dreamt that she was perused through an airport by a wolf; she escapes by jumping from an open jetway. This turned out to be precognition: she WAS chased through the airport – but by a murderer; a rogue cop - Detective Wolfe.
If this model is the correct one, then psychics would have to testify as expert witnesses. That is, they would have to explain not only what they saw/heard/experienced, but how it should be interpreted. Obviously, the other side would be free to offer its own expert testimony in rebuttal.
Equally obviously, there would have to be some sort of universally-understood qualification process for psychic expert witnesses. And, as I suggested above, there would have to be a general finding that “psychic powers” are an accepted field from which to draw expert conclusions.
Today, a fingerprint expert can testify on the issue of fingerprint matching without having to defend the entire science of fingerprinting. A DNA expert may offer conclusions about DNA evidence without having to defend DNA evidence. The court may take judicial notice of the general acceptibility of DNA science. But at one time, DNA evidence was new, and there was not such firm ground for courts to rely upon.
DNA testing was in those days subject to a “Frye hearing” or a “Daubert hearing.” This is based on the two cases that have set standards in use throughout the country on the admissibility of new scientific evidence. The Daubert standard, to use the test that’s applicable to federal courts and many states, calls for the judge to assess whther the new field, technique, or method has been:
[ul]
[li]sufficiently tested[/li][li]subjected to peer review and publication[/li][li]determined to be accurate[/li][li]generally accepted[/li][/ul]
The admission of psychic expert testimony would have to pass those same hurdles. If psychic powers have passed those tests, then a judge could permit a psychic expert witness to testify. The psychic would still have to establish his own particular qualifications. (That is, just because DNA scientific testimony is accepted does not mean that I, personally, may serve as an expert witness on DNA). That latter qualification is done through a voir dire-type examination of the witness; he is typically asked such questions as:
[ul]
[li]His resume - what academic or employment qualifications he has [/li][li]What certification, accreditations, awards, or official acknowledgements has he received in his field[/li][li]His publications - books, papers, or articles he has authored[/li][li]Books, papers, articles or authors he has read in his field [/li][li]Classes, conferences or meetings he has attended related to his field[/li][/ul]
Based on the answers to those types of questions, the judge will decide if the particular witness is qualified and may answer as an expert.