A party may impeach a witness by showing defects or weaknesses in the witness's ability to perceive.

Fed. R. Evid. 807 ("A statement not specifically covered by Rule 803 or 804 but having equivalent circumstantial guarantees of trustworthiness, is not excluded by the hearsay rule, if the court determines that (A) the statement is offered as evidence of a material fact; (B) the statement is more probative on the point for which it is...A statement not specifically covered by Federal Rule of Evidence 803 or 804 or by comparable State rules, but having equivalent circumstantial guarantees of trustworthiness, is not excluded by the hearsay rule, if the court determines that (A) the statement is offered as evidence of a material fact; (B) the statement is more probative on the point for which it is offered than any other evidence which the proponent can procure through reasonable efforts; and (C) the general purposes of these rules and the interests of justice will best be served by admission of the statement into evidence.

Fed. R. Evid. 804(a)(3) (declarant is unavailable if declarant "(3) testifies to a lack of memory of the subject matter of the declarant's statement").For purposes of the hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule, a declarant is "unavailable" within the meaning of Rule 804(a) or a comparable State rule if the declarant testifies to a lack of memory of the subject matter of the declarant's statement; but a declarant is not "unavailable" if such claim of lack of memory is due to the procurement or wrongdoing of the proponent of a statement for the purpose of preventing the witness from attending or testifying.

Fed. R. Evid. 412(b)(2) ("In a civil case, evidence offered to prove the sexual behavior or sexual predisposition of any alleged victim is admissible if it is otherwise admissible under these rules and its probative value substantially outweighs the danger of harm to any victim and of unfair prejudice to any party.").Under some rape shield laws other sexual conduct or sexual disposition of alleged victim is admissible in a civil proceeding for sexual misconduct if the probative value of the other conduct or of the victim's sexual disposition substantially outweighs the danger of harm to the alleged victim and the risk of unfair prejudice to a party.