The Ownbey-Zirkle ESP experiment at Duke was criticized by parapsychologists and skeptics.  Ownbey would attempt to send ESP symbols to Zirkle who would guess what they were. The pair were placed in adjacent rooms unable to see each other and an electric fan was used to prevent the pair communicating by sensory cues. Ownbey tapped a telegraph key to Zirkle to inform him when she was trying to send him a symbol. The door separating the two rooms was open during the experiment, and after each guess Zirkle would call out his guess to Ownbey who recorded his choice. Critics pointed out the experiment was flawed as Ownbey acted as both the sender and the experimenter, nobody was controlling the experiment so Ownbey could have cheated by communicating with Zirkle or made recording mistakes.