How background complexity impairs target detection

Camouflage is frequently used by animals for concealment and thereby improves survival. Typically, it is the animal's own colour and patterning that are expected to affect its detectability; however, the complexity of the background can also have an influence. Although there is a growing literature examining this, the underlying exact mechanism is unknown. In this study we addressed this issue by using humans as proxy 'predators' in a computer-based search task and monitoring their detection times for targets on varying backgrounds. By using artificial greyscale targets and backgrounds, we were able to isolate and manipulate the normally covarying factors that comprise 'complexity' in natural habitats. We show that reduced detection was explained not by greater information content (entropy) or higher variance in the background's features per se, but instead by reduced signal-to-noise ratio in the visual features that potentially distinguish target from background. This raises questions about when the term complexity should be used, and how observers learn the characteristics of a background.