Electronic scanning technique for continuous tracking of human eyeball movements

The design of a system for studying human eyeball movements is presented. The system output provides eyeball location and pupil size in the form of step-wise voltages which are up-dated a minimum of 4000 times per second. Eye movements up to ± 45 degrees in two dimensions can be tracked. The frequency response of the system ensures continuous tracking of all eye movements including the fastest saccades. The method employed is a photoelectric scan which uses feedback to lock onto the pupil and follow its movements. In the final system, this is performed by a scanning photo-multiplier tube which electronically dissects an optical image of the eye. To check the feasibility of the proposed system before the scanning photomultiplier is purchased, the work is performed in two parts: first the circuitry required to perform the scan is developed and tested without the use of a scanning photomultiplier tube; then an experiment is performed which simulates the scanning photomultiplier and enables the over-all system performance to be evaluated. In the first part, a system is constructed which performs similarly to the final system except that the electronic dissection of the image is performed using an oscilloscope in conjunction with a simple photomultiplier instead of the scanning photomultiplier. This "flying-spot system" is used to test the circuitry required to perform the scan: the circuitry proves to be entirely, satisfactory. In the second part, the simulation enables the signal noise ratio of the scanning photomultiplier to be predicted. On the basis of this, a recommendation is made to purchase the scanning photomultiplier and to construct the complete system.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat