The quality and reliability of the functioning of the man-machine control systems, that is, systems where the human operator is a part of their control loop, largely depends on his/her psychophysiological characteristics. Man-machine systems are designed to control complex technical objects and systems, technological processes and aviation traffic. Malfunction of these systems can lead to human losses and manmade disasters. Therefore, it is important to study the work of a human operator in such a system. One of the most important functions performed by a human operator is a visual search for objects displayed on the screen. The dependencies of the probability of detection of the object on its contrast with the background, the background luminance, the size of the object and the search time were first investigated and obtained by the author as a result of the experiments. These characteristics of visual search allow us to optimize the work of the human operator. The obtained results can be used in the design and evaluation of the efficiency of the “man-display” systems.