What is the value of witness testimony in a sexual assault case?

In The Queen v. Nikolovski, supra, at 409, 412 Cory J. outlined the value of witness testimony when he stated: As a minimum it must be determined whether the witness was physically in a position to see the accused and, if so, whether that witness had sound vision, good hearing, intelligence and the ability to communicate what was seen and heard. Did the witness have the ability to understand and recount what had been perceived? Did the witness have a sound memory? What was the effect of fear or excitement on the ability of the witness to perceive clearly and to later recount the events accurately? Did the witness have a bias or at least a biased perception of the event or the parties involved?