Visual search in continuous, naturalistic stimuli

In standard visual search experiments, subjects look for a target item among distractor items. Targets and distractors are generally presented as isolated entities on a blank background. Do theories based on results of such experiments have any application to the real world of spatially continuous stimuli where "items" are not so conveniently delineated? Experiment 1 examines search for conjunctions of color with form and with orientation in novel stimuli designed to resemble aerial views. As with artificially isolated items, conjunction search with these complex stimuli is highly efficient, holding out the promise that models of visual search based on laboratory data can be extended to real-world situations. Experiment 2 shows that some "serial" searches are made significantly less efficient when items are embedded in these specific naturalistic backgrounds. This suggests that even classic serial searches rely on some parallel processing--the processing required to locate the "items" to be serially searched.