Reaction time to incremental and decremental target luminance changes at various photopic background levels

Abstract

The experimental data clearly confirm a general luminance-contrast principle established in this laboratory on other visual functions: For contrasts just beyond some critical near-zero value, visual performance is determined by the prevailing retinal illuminance of that component, either target or background, which has the higher illumination level. Thus, for positive contrasts, RT progressively decreases to an asymptotic value as target luminance (the higher component) is increased. However, as negative contrast is increased (i.e. as target luminance is decreased at any background level), RT remains constant at a value which is determined by the prevailing background illumination level (now the higher component); the higher the prevailing background, the lower is the corresponding value of RT. A schematic model which predicts the results of these contrast effects is presented. The data on positive contrast were used to generate typical photopic intensity-discrimination curves, using several selected RT values as response criteria.