This is a technical survey of the researches on synthesizing a model of the visual system of an animal, or an electronic eye such as a pattern recognizer for which ingenious mechanisms of biological systems are heuristics. These researches are reviewed from a standpoint of visual information processing.
This survey includes the models of photoreceptors, the models of neural interactions, in a retina, the models of the visual feature extraction from optical patterns, and the models of the recognizing system which have an ability to learn characters or figures.

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Studies were made, to elucidate problems concerned with pacemaker electrodes and stimulation threshold.
1) Electrolysis of electrodes was compared among various stimulation waveforms used for cardiac pacemaking by using gelatinized physiological saline solution. The degree of electrolysis was judged by the degree of metal ion tincture to the gelatinized solution around the electrodes. Less electrolysis was observed with a symmetrical biphasic pulse, a condenser blocked pulse and a monophasic rectangular pulse in the descending order, when they were used as pacemaking pulses. The direct induction pacemaker was employed for generating the symmetrical biphasic pulse.
2) There was an optimal surface area of an electrode for the heart to be paced with a minimum electricity. Electrical threshold was not affected significantly by the distance between bipolar electrodes or their locality on the heart. Monopolar stimulation had lower threshold than bipolar stimulation.
3) A Hunter-Roth electrode, a coiled electrode, a cored coil electrode, a screw-in electrode and a catheter electrode were examined in regards to electrical threshold, tissue reaction and structual strength. The coil type electrodes and catheter electrode were satisfactory in all respects during long term observation, while the Hunter-Roth electrode failed of functioning in a relatively short period of time.
4) Stimulation threshold was changed to some degree by physiological conditions such as myocardial anoxia or autonomic nervous disturbances, but not significantly from the practical viewpoint of cardiac pacemaking.
5) Clinical experiences have shown that the elevation of threshold encounterd was brought about mostly by infection around the electrodes. The infectious granulous tissue or scar formation around the electrodes separated them from normal myocardial tissue, thus reducing transmembraneous current density of myocardial cells.

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In the design of mechanical transducers for picking up the vibrations of the surface of a biological subject, it is often emphasized that the transducer should be convenient in the attachment, that it should retain constant characteristics in spite of the changes in its relative position to the surface, and that, in case unusual large disturbances come in because of unexpected motion of the subject, the transducer and the following electronic instruments should recover their normal functions rapidly. As an example of the transducers having excellent characteristics from these points of view, this paper considers a displacement transducer with a coupling by the viscosity of silicon grease. A small cylinder attached to the surface transmits the displacement, through the silicon grease filled in a very narrow gap, to the membrane with strain-guages. It is calculated and experimentally verified that, due to the nonlinear viscosity of the silicon grease, the effect of artefacts is greatly reduced. An experimental set-up of the transducer has the frequency response of 0.3 Hz to 20 Hz, and is found to be very convenient and useful in clinical uses such as plethysmography and for other purposes.

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The transfer characteristic of the carotid sinus pressure control system had been studied by the frequency response method, opening the physiological closed loop. However, in dogs we studied the system with the loop closed, inserting a T-shaped tube in the unilateral common carotid artery and applying a pressure impulse to the carotid sinus as a disturbance, and obtained the transfer function from the endosinual pressure to the aortic pressure, calculating the transient pressure response. The result was considered to be similar to the previously reported characteristic by the other methods. So this method proved to be useful to obtain a characteristic of a biological system in physiological conditions.

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