By John DiMotto
In Wisconsin, every person is competent to be a witness. However, this does not mean that what a witness says is automatically worthy of belief. The credibility, that is, the believability of what a witness says when he/she give testimony, is affected by cross examination and by contradiction by other witnesses and evidence. Ultimately, the trier of fact will determine which witnesses to believe and what evidence to accept.
One of the ways that the credibility of a witness is challenged is by attacking the testimonial capacity of a witness. Testimonial capacity implicates the ability to perceive, remember or narrate. If it can be established that a witness was unable to perceive an event, remember an event or relate what he/she saw, the trier of fact may discount the testimony to the point where it is given no weight. Testimonial capacity relates to whether the witness is innocently mistaken not if the witness is lying.
A witness may be cross examined regarding his/her mental or physical condition where such matters have bearing on his/her credibility. For example, if a witness is hard of hearing, needs a hearing aid, and was not wearing his/her hearing aid, that is a fact that a trier of fact may consider in determining whether to believe the witness' testimony regarding a conversation the witness says he/she heard.
In terms of the cross examination of a witness as to a mental or physical condition, it must be one that was in existence:
1) at the time of testifying, or
2) at the time to which the testimony refers, and
3) the condition must be relevant.
Relevancy is an important consideration when considering testimonial capacity. For example, a person may color blind but if the witness' testimony is based on hearing something the color blind condition (vision defect) would be irrelevant. It is further important to note that mere physical or mental impairment, without more, is not sufficient to affect credibility. There must be a connection between the affliction and the reliability of the witness' testimony. The fact that a person has been intemperate in the past regarding drug or alcohol use, or the fact that a person has had a mental condition (i.e. bipolar diagnosis) in and of itself is not generally admissible.
Defects in testimonial capacity are a non-collateral form of impeachment. This means that if the witness denies having a hearing problem, this denial can be challenged by calling a witness or introducing affirmative evidence of a hearing problem. However, the right to attack one's condition is not unlimited. The trial court must always exercise discretion and weigh the potential unfairness and embarrassment against the materiality and relevancy of the evidence.
In my next post in this series on Impeachment and Rehabilitation Evidence, I will look at bias, prejudice and interest issues.