An Electronic Photoreceptor Sensitive to Small Changes in Intensity

We describe an electronic photoreceptor circuit that is sensitive to small changes in incident light intensity. The sensitivity to changes in the intensity is achieved by feeding back to the input a filtered version of the output. The feedback loop includes a hysteretic element. The circuit behaves in a manner reminiscent of the gain control properties and temporal responses of a variety of retinal cells, particularly retinal bipolar cells. We compare the thresholds for detection of intensity increments by a human and by the circuit. Both obey Weber's law and for both the temporal contrast sensitivities are nearly identical