Computer engineering techniques for collecting and processing bio-medical signals associated with human eye movement
This thesis is concerned with the investigation of two types of eye movements; smooth pursuit, and saccadic eye movement, each of which was analysed under normal condition, and then after the administration of alcohol. Parameters of interest in a selected range were measured using the novel approaches developed in this thesis and the results of a series of different tests compared. Much of the early work done in this area was based on minicomputers. Obviously, a microcomputer based system would be welcome because of costs, and the fact that they are readily available in many hospitals and health centres. The work reported here was carried out using the BBC microcomputer system, since it is inexpensive and commonly used in UK health institutes. The experimental facilities constructed for the work of this thesis were driven by the intention of producing a system free from many of the weaknesses in existing procedures, and to develop an essentially new approach to the problem. The starting point of the research described depends on the fact that whenever the eyes are moved a signal appears at the two poles of the eyes. This signal is known as the resting potential, or standing potential, with the cornea several mV positive with respect to the back of the globe. This potential is generated by the retinal pigment epithelium. By influencing the eyes to move in certain directions, and at certain velocities and frequencies, information can be gathered by further analysis of the signal captured. The signal captured is found to be very small (in the μV range), therefore an amplification of the signal is required, the amplifier needed must have specific features to meet the requirement of high input impedance so the signal is not distorted. This was achieved using a specially designed instrumentation amplifier. Noise which is always present in the signal, was rejected using filtering in analogue and digital forms. The analogue filter was a Butterworth filter with a frequency passband in the range between 0.1-30Hz. The digital filter chosen was the Hanning Window type. To ensure the safety of the person taking the tests care must be taken to isolate all equipment, consequently the signal collecting electronics was powered by batteries. The collected signal was interfaced to the computer using the 1MHz BUS of the BBC microcomputer. A second computer was used so that one of them can process the captured signal while the other generates a moving spot on the screen of a monitor as a stimulus for eye movement The collected signals are then processed in both the time and the frequency domain. The use of frequency domain techniques is a particularly useful form of analysis in the treatment of eye movement potentials, and is shown to extend the information that can be extracted from such signals.