Abstract
Purpose :
The Ferry-Porter law states that the critical flicker fusion frequency (CFF), measured psychophysically, is linearly correlated with the logarithm of the mean luminance. In the current study, we established the relationship between the CFFs of L- and M-cone driven ERGs and mean luminance.
Methods :
We measured ERG responses in five normal trichromats (three females) to L- and to M-cone isolating sinusoidal modulation (18% cone contrast) at different temporal frequencies encompassing the CFF (defined as the frequency where the ERG is just not discernable from noise). The measurements were performed at seven mean luminance levels ranging from 2.84 to 284 cd/m2.
Results :
The ERG amplitudes as a function of temporal frequency could be described by a simple exponential function when the frequencies were close to the CFF. From these functions the CFFs could be determined. Similar to psychophysical data, it was found that the CFFs for L-cone driven ERGs were higher than those for M-cone driven ERGs and that the CFFs depended linearly on the logarithm of the mean luminance. However, the slopes of the linear regressions were steeper than those found in psychophysical measurements. Furthermore, in ERG measurements, the slopes for L- and M-cone isolating stimuli were similar, whereas they were steeper for L-cone stimuli in psychophysical measurements.
Conclusions :
The CFFs determined with ERGs adhere to the Ferry-Porter law. However, the dynamic range of CFFs is smaller in comparison to psychophysical measurements. In addition, whereas L- and M-cone driven CFFs differ only by a constant factor in ERG measurements, they differ in a more complex manner psychophysically. These differences possibly have a cortical origin.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.