The 'OFF' response of the human electroretinogram does not contribute to the brief flash 'b-wave'

It has been assumed that the 'ON' and 'OFF' responses of the human electroretinogram (ERG) interact to produce a single waveform when brief flashes are used. To test this assumption, we examined the separate effects of stimulus intensity, the level of retinal illuminance and stimulus duration on the ERG. Both 'ON' and 'OFF' response amplitude decreased as stimulus intensity was decreased and as the level of retinal illumination was reduced. When stimulus duration was reduced, the amplitude of the 'OFF' response decreased; however, the amplitude of the 'ON' response increased. Summing of the 'ON' and 'OFF' response waveforms could not account for the increased amplitude in response to brief stimuli or for the changes in ERG wave shape. These results indicate that there is not a significant corneally recordable 'OFF' response elicited by brief stimuli, such as those commonly used to record the flash ERG.