A trial court has the authority -- under some circumstances -- to disqualify a person with a mental infirmity or disorder from serving as a witness.

United States v. Goodchild, 25 F.3d 55, 61-62 (1st Cir. 1994) (upholding trial court's admission into evidence of the telephone statement memos as business records because "[the statement memos met] the strictures of the....The hearsay exception for "business records" created by Federal Rule of Evidence 803(6) or a comparable State rule applies only (i) the record is based on the personal knowledge of an entrant with a business duty to record the event or other such matter or (ii) if the record of the event is based on the personal knowledge of a person who had a business duty to transmit the information about the event or other matter to the person or persons who made the record and had a business duty to do so. A person has a "business duty" if the person has a duty to an organization by reason of law, contract, employment relationship, or other such matter to record or report an event, condition, opinion, or other matter to which the business records exception to the hearsay rule may apply.

Cf. United States v. Bedonie, 913 F.2d 782, 789-781 (10th Cir. 1990) ("Fed.R.Evid. 601 provides that '[e]very person is competent to be a witness except as otherwise provided.' 'A witness may not testify to a matter unless evidence is introduced sufficient to support a finding that...It is possible that persons may be disqualified from serving as witnesses on grounds not expressly enumerated in codes of evidence or by general common law principles -- on unenumerated grounds such as age, illness, sensory defects, defects in intelligence, lack of understanding, inability to communicate, defects in memory, and inability to be truthful.

United States v. Kappell, 418 F.3d 550, 555-556 (6th Cir. 2005) (holding that the testimony of the victims did not violate defendant's right to confrontation because "the two witnesses [the children] did testify and were....The admission of a statement made other than at the trial does not violate the right of confrontation guaranteed to a criminal defendant by the Sixth Amendment to the U.S. Constitution if the maker of the statement -- the declarant -- testifies at the trial.