ERG off-effects produced by short duration stimuli

Variable duration square wave pulses of 633-nm light were used to produce electroretinograms (ERG's) in a human subject. When the stimuli were presented on a white light background, the records obtained for stimulus durations greater than 70 msec showed a clearly separated off-response while those of shorter durations did not. By subtracting a common "on-effect" from the ERG's produced by short duration stimuli, the previously unseen off-effect was isolated from records produced by stimulus pulses as short as 5 msec. It appears that the marked increase in b-wave amplitude associated with these short duration stimuli can be attributed to an interaction between "on" and "off" components of the ERG.