[Clinical application of time dependent perimetry (9). The relations between stimulus area and double flash...

Double flash resolution (DFR) and critical flicker fusion frequency (CFF) at the center of the visual field and the 5 degrees superior visual field were measured in normal subjects as a function of the stimulus area. Six stimulus sizes, ranging from a visual angle of 5' to 3 degrees 36' were used. The following results were obtained. First, the CFF increased as the stimulus area became larger at both the center and the 5 degrees superior visual field. Secondly, at the center of the visual field, the DFR initially increased as the stimulus area became larger and then decreased. Thirdly, at the 5 degrees superior visual field, this inhibitory phenomenon was also encountered with great individual variations and was not so evident as at the center of the visual field. Fourthly, the increasing rate of sensitivity was found to be greater at the 5 degrees superior visual field than at the center of the visual field in both CFF and DFR. From these results, we speculated that the CFF was detected by the transient system, which exhibited a weaker or no surround inhibition, and that the DFR in the center of the visual field was detected by the sustained system, which exhibited great surround inhibition. The DFR at the 5 degrees superior visual field could be detected by both transient and sustained systems.