Visual perception’s purpose is to generate consistent representations of task-relevant scene features (e.g., object reflectance) despite fluctuation in task-irrelevant scene variables (e.g. illumination and reflectance of other nearby objects). For a study, researchers offered a threshold-based psychophysical paradigm to investigate such stability in the context of the perceptual perception of lightness. 

They used a two-alternative forced-choice paradigm in which the reflectance of the background objects is randomized across the two intervals of each trial to assess how variation in the reflectance functions of background objects affected thresholds for discriminating the achromatic reflectance of a target object (task-relevant property) in rendered naturalistic scenes. They manipulated a statistical model of naturally occurring surface reflectances to regulate the degree of fluctuation in background reflectance. Discrimination thresholds were essentially constant for modest background object reflectance fluctuation, showing that observers’ internal noise influences the threshold in the domain. 

As the diversity in backdrop object reflectance rose, its impacts began to dominate performance. Investigators defined the impacts of task-irrelevant variation in terms of equivalent noise, which was related to the inherent accuracy of the task-relevant perceptual representation, using a model based on signal detection theory. Although naturally occurring background object reflectance variation does intrude on the perceptual perception of target object brightness, the effect was minor – within a factor of two of the corresponding noise level established by internal noise.