- Sensory Deficiencies – A witness may be impeached by showing, either on cross-examination or by extrinsic evidence, that his ability for perception and recollection was so impaired as to make it doubtful that he could have perceived those facts.
- Examples of sensory deficiencies—bad eyesight, bad hearing, mental retardation, forgetfulness, intoxication at the time of event or while on the witness stand.