noun. 1. with regard to a trial and error scenario, an assistant to the experimenter who takes on the role of a participant but also whose actions are practiced before the experiment ensues. The actual partakers in the experiment are occasionally called naive participants. 2. with regard to parapsychology, a person who helps an alleged psychic by discretely supplying them with data about a customer's worries, inclinations, past, or current scenario, thereby producing or reinforcing the perception of the psychic's paranormal capacities.