Abstract
Visual search is a critical task for many life-saving professions; Lifeguards scan for struggling swimmers, airport baggage screeners search luggage for dangerous items, and radiologists examine X-rays for tumors. While these jobs often require searching very cluttered environments for multiple targets (e.g., multiple tumors in an X-ray), most laboratory research is restricted to relatively uncluttered displays with only one target. It is known that clutter can negatively influence search (e.g., Verghese & McKee, 2003), and that a second target is less likely to be detected in a multiple-target search array when a first target has already been found (e.g., Tuddenham, 1962; Berbaum et al., 2010), but do these factors interact? Little is known about interactions between target number and visual clutter, and understanding this can inform both search theory and professional searches. Here we explored visual clutter in a multiple-target search paradigm where there could be 1 or 2 targets present on a given trial, and targets appeared in varying levels of clutter. Three categories of clutter were defined based upon the number of distractor items located within a 100-pixel radius from the center of a target—no clutter (no distractors within the radius), minimal clutter (1 distractor within the radius), and high clutter (2+ distractors within the radius). There was a significant interaction between target number (1 vs. 2) and clutter (no, minimal, or high): Clutter had no effect on detecting a single target or the first target in a dual-target trial, but clutter significantly reduced detection of a second target in a dual-target trial. Multiple-target search accuracy is highly sensitive to contextual influences (e.g., Cain, Dunsmoor, LaBar, & Mitroff, 2011), and the current results reveal a specific effect wherein relatively more difficult targets (i.e., the second target in a dual-target trial) are especially influenced by visual clutter.
Meeting abstract presented at VSS 2012