Abstract
Adapting to the characteristics of a visual environment may enhance the salience of novel stimuli (Barlow, in Vision: Coding and Efficiency, 1990). We examined eye movements when searching for a target on familiar or unfamiliar backgrounds. Observers searched for a colored circle or a uniquely colored ellipse at random locations on a 30 by 40 deg dense background of colored ellipses (similar to finding a fruit among foliage). Colors in the backgrounds randomly varied along the LM or S cardinal axes, while test colors varied over a range of contrasts along the cardinal or intermediate axes. Background elements also varied randomly in luminance. Observers searched for the targets on a given background before or after adapting to different backgrounds. Fixations were recorded with a CRS video eyetracker, with detection requiring 0.5 sec within 2.5 deg of the target. Search times decreased (from up to several sec) with increasing distance in color space between the target and background, and were consistently faster when subjects searched on backgrounds drawn from the same color axis they had adapted to than from the orthogonal axis. These results help reveal how visual salience and therefore visual search vary in novel versus familiar contexts.