Cone ERGs to Flash Trains: The Antagonism of a Later Flash

The human cone electroretinogram (ERG) to flash trains and double flashes at different interflash intervals was studied. A double ganzfeld stimulator was used in which computer controlled flashes were presented independently in the presence of strong rod saturating backgrounds. Corneal ERGs were examined at different frequencies of flash train presentations. Flash trains with individual flashes of high frequency (100 Hz) simulate a cone ERG to light pulses of long duration by producing a corneal positive off-response (d-wave) time locked to the cessation of the train. A second flash can reduce and delay the cone b-wave produced by a first flash. This effect is maximal when the second flash occurs 10-12 msec later. There is an antagonistic mechanism in the cone system of the retina which can catch and reduce the cone b-wave produced by an earlier flash.