Losses of flicker sensitivity during dark adaptation: effects of test size and wavelength

The losses of flicker sensitivity that occur during dark adaptation following extinction of a bleach depend greatly on the test stimuli that are used to measure those losses. Generally, the larger the test size is for a given test wavelength, the later is the loss of flicker sensitivity; for sufficiently large tests, losses become progressively more gradual. Similarly, the shorter the test wavelength is (between about 660 and 580 nm) for a given test size, the later is the loss of flicker sensitivity; for sufficiently short test wavelengths, losses become progressively more gradual. Although the pattern of flicker sensitivity loss as a function of test size is the same both foveally and parafoveally, foveal losses occur later and/or more gradually for a given test stimulus. The results suggest that losses of flicker sensitivity occur when spectrally antagonistic response(s) to the test are no longer adequate to maintain the flicker-response to that test. The results suggest also that the adequacy of such spectral antagonism depends on the local adaptation state of the retina, which becomes increasingly more light-adapted with increasingly large test size.