Twin-flash response as a function of flash diameter

The response to twin increment flashes was determined as a function of the flash diameter. It was found that the response was subject to an inhibition effect but only above a certain flash diameter and a certain delay time. These results would seem to indicate that the spatio-temporal point-spread function of the human visual system consists of an area of summation surrounded by an interaction-free zone, which in its turn is encircled by an inhibition region. Some consequences of these findings for spatial and temporal transfer curves were discussed and verified experimentally, while the stimulation by decrement flashes and doublets (increment-decrement twin flashes) was also investigated.