Localization and discrimination of "pop-out" targets

In parallel visual search, a target pattern "pops out" among distractors rapidly, requiring no effort, regardless of distractor numbers. The localization and discrimination of "pop-out" targets was investigated for this research note using similar multiple displays to those used in Sagi and Julesz's [(1985a) Science, 228, 1217-1219] and Folk and Egeth's [(1989) Journal of Experimental Psychology: Human Perception & Performance, 15, 97-110] studies. The stimulus display contained 2, 5 or 10 oblique target line segments embedded in vertical distractor lines. In the first localization task, the observer indicated whether all the targets were in other positions. The second localization task was otherwise identical to the first one, except that the number of critical inside-corner positions was four. In the discrimination task, the observer reported whether all the target lines had the same orientation, or whether one of them differed in orientation from the others. Reaction times for correct responses were measured in all three tasks. The results showed that target discrimination took place in parallel, but target localization was a "serial" process, i.e. the localization time depended on the number of targets and critical locations to be checked.