Visual circuit

A visual circuit was a grey Dalek's means of vision. During the Dalek-Movellan War, the Fourth Doctor used his hat to block such a Dalek's eyestalk, impairing its visual circuit. (TV: Destiny of the Daleks)

A different visual circuit was used as a monitor in the office of Tobias Vaughn at International Electromatics. (TV: The Invasion)