L*-cone-driven responses increased, and the phase shifted rapidly after the mean luminance was increased from 0.4 to 8.8 cd/m
2, with no further changes in either amplitude or phase during the following 10 minutes of adaptation. The reversed change in mean luminance resulted in an equivalent decrease in response amplitude and a phase shift (although the responses were small and thus the phases not very reliable at 0.4 cd/m
2). From this we conclude that adaptation in L*-cone-driven responses probably is completed during the first measurement after the change in mean luminance and, therefore, probably within seconds. A higher temporal resolution might give more information about the time course of L*-cone-driven adaptation to high luminance levels. Yeh et al.
42 also found that the responses of primate ganglion cells in the cone pathway adapt rapidly (i.e., within seconds). Responses to luminance stimuli were equally fast when adapting to the 8.8 cd/m
2, indicating that these responses were mainly L*-cone driven and that the responses to luminance stimuli rapidly switch from rod- to L*-cone driven. The similar adaptation dynamics recorded with L*-cone-isolating (55% contrast) and luminance (100% contrast) stimuli at 8.8 cd/m
2 suggest that the speed of adaptation does not depend on the stimulus contrast. As cone-driven responses reflect the activity of both ON and OFF bipolar cells, adaptation effects of both cell types may interfere. This complicates the interpretation of the ERG data. Our data reveal that the responses to L*-cone and luminance stimuli change very fast after an increase in luminance without any further changes in amplitude or phase, indicating that cones fully adapt within the first recording (30 seconds) within the used range of luminance levels. In a recent study, we showed that the responses to sine-wave luminance stimuli (100% contrast) hardly changed after a change from 1 to 25 cd/m
2 white background (after previous adaptation to 1 cd/m
2) in LIAIS mice.
21 Adaptation of photopic (i.e., mainly cone driven) flash ERGs to 25 and 40 cd/m
2 (i.e., 1.4 and 1.6 log cd/m
2) backgrounds (after complete dark adaptation) took several minutes. Possibly, the different light levels and different stimulus types employed in the previous study caused the differences in results. Cameron and Lucas
23 showed in Gnat1
−/− mice, lacking functional rods, that flash ERG responses increased during a 20-minute period of light adaptation to a 5.7 log cd/m
2 background after a period in the dark. This indicates that different adaptation processes may be involved in ERG responses to flashes upon a background and to temporal modulations around a mean luminance and chromaticity.