1. An eye-tracker system comprising: (a) a light source; (b) a television camera producing video signals; (c) a frame encoder circuit connected to the video signal output from the camera for encoding the signals at at least two threshold levels and storing said encoded data for a two dimensional area within said frame in a cache memory, said threshold levels being programmable; and (d) a computer in communication with said encoder circuit at least via its data bus and address bus for programming said threshold levels, controlling the encoder and accessing data in said cache memory; (e) said computer having an associated main memory with a stored task for reading the cache memory and interactively controlling the frame encoder including a subtask for finding the corneal reflection of an eye upon which the camera is focussed by lowering the upper threshold until the brightest spot on the frame is detected and having a subtask for finding the pupil of the eye by raising the lower threshold at least until the border between the pupil and the iris of the eye upon which the camera is focussed is defined and having a third subtask for finding the center of the corneal reflection and the center of the pupil and establishing the vector from the center of the corneal reflection to the center of the pupil.