Chromatic contrasts predict human target detection in a natural search task

Abstract

Natural scenes are visually complex, with dynamic variation in colour and luminance presenting challenges for detecting salient objects. However, the cues guiding human detection under such natural conditions remain largely untested. We placed custom-built coloured targets in a forest-like setting and quantified their contrasts against natural backgrounds using human visual models. Across human observers (n = 51), detection performance rose sharply with hue and saturation contrast, whereas luminance contrast--long considered a primary driver of visual search--contributed little explanatory power. Strikingly, even large changes in ambient light chromaticity barely altered detection, despite the patchy illumination of the habitat. Under these naturalistic conditions, hue and saturation contrasts were stronger predictors of detection than luminance contrast, providing a rare, field-based test of visual models widely applied across human and animal vision research.