Aberrant flicker sensitivity revealed by heterochromatic modulation photometry

Abstract

Heterochromatic modulation photometry is a method in which a series of fixed standard luminance/test luminance ratios are presented, and at each ratio the modulation depth of the pair is reduced in tandem until the observer reports that flicker disappears. The expectation is a distinct minimum modulation sensitivity at the standard/test ratio representing the luminance match. At other luminance ratios, flicker sensitivity should vary with the luminance difference between standard and test. We have devised theoretical templates to describe modulation sensitivity as a function of standard/test ratio. The results of other flicker studies indicate that flicker sensitivity would be expected to fall within the domain between a linear system (sensitivity proportional to the amplitude of modulation) and a Weberian system (sensitivity proportional to percent modulation). Using ‘red’ and ‘green’ lights, at low photopic luminances this expectation is well realized. At higher luminances and when the ‘red’ light is of higher luminance than the ‘green’, observers are much less sensitive to modulation than the models predict.