Edinburgh Napier University

  Little is known about visual search for targets on natural, textured backgrounds, or about the capacity of biological camouflage patterns to provide protection across a range of backgrounds. The experiments described address both these problems. Observers searched under diffuse daylight for a camouflaged target on a flat, natural surface, subtending approximately 35 × 20°, while wearing a lightweight portable eye tracker. The targets were life-size images of four different moth species, varying in luminance contrast and size of pattern elements. They were printed on paper and cut out. Two backgrounds were approximately uniform in colour (paving slabs, stucco wall), while two consisted of distinct objects varying in colour (stone chips, dead leaves). The identity, position, and orientation of the target varied randomly between trials. The background had a significant effect on search time, which was longest for the stucco wall, and shortest for the paved surface. The rank ordering of difficulty of search on the four backgrounds could not be explained by differences in first-order properties (mean luminance, contrast) between their images and those of the moths, nor by the strength of luminance gradients at the outlines of the moths. The results suggest that search follows segregation of a scene into distinct solid elements