Figure 1.

Experimental arrangement for electroretinogram (ERG) recording. A high intensity white light emitting diode was driven by a custom-built voltage-to-current power supply to generate 1 s flashes of 100 lm. The LED light was reflected onto the entire cockroach face by a concave white plastic reflector located 50 mm from the surfaces of the compound eyes. Sharpened tungsten electrodes were inserted just below the surface cornea, and a reference Ag/AgCl electrode through a small hole at the top of the head. ERGs varied strongly with position across the eye, as illustrated. Traces show mean and standard error responses to 10 repeated 1 s flashes. Standard errors were so small that their traces were obscured by the mean value traces.