Inquiry into the admissibility of evidence showing mental deficiency in a witness is suggested by State v. Teager, a recent decision of the Supreme Court of Iowa. Defendant, charged with assault with intent to commit rape, offered to prove by a school teacher that the complaining witness, a child twelve years old, was "at least two years behind in her school work . . . subnormal mentally . . . and ought to be in an institution . . . . " No objection had been made to the competency of such witness. It was held that the evidence was correctly excluded by the trial judge. The court indicated, however, that had the capacity of the witness been challenged when she was offered, and had she passed the examination and been sworn, the testimony would have been admissible as bearing on her credibility. The reported cases indicate wide divergence in result, grounded on the peculiar purpose for which the evidence is presented. As a preliminary matter, therefore, the situations may be considered where mental condition is conceivably vital.
Erwin B. Ellmann,
WITNESSES - EFFECT OF MENTAL DEFICIENCY ON COMPETENCY AND CREDIBILITY,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol36/iss5/7