Tayna Simulation Four was a holoprogram created on the holodeck of the USS Enterprise-D based on Tayna's deposition concerning the events leading to the explosion of the Tanuga IV research station and the death of Dr. Nel Apgar.
This program showed Tayna and Nel discussing the events of Tayna Simulation Three. Tayna declared that she was going to call the authorities and Nel told her not to because he would do it himself. Nel then sat down and began to activate the Lambda field generator. The program ended when Tayna left the station. (TNG: "A Matter of Perspective")