The temporal relationship among detection, localization, and identification in visual search

Purpose. This study investigated the temporal relationship among detection, localization and identification in visual search with disjunctive features, as well as the role ofiarget-distractor discriminability in these searches. Methods, Ten observers performed three search tasks: a) They detected either a tilted red, a tilted blue, a green horizontal or a green vertical target; b) They identified a green (horizontal vs. vertical) or a tilted (red vs. blue) target; c) They localized the target on the right or the left half of the display. In all three tasks the target was present in 2/3 of the trials; the number of distractors varied from 6 to 36; the display subtended 6° by 6° and was present for 104 ms to avoid eye movements while the display was present. Results. The detection task was performed faster and more accurately than the identification and localization tasks. In addition, when the target was present, localizing the target was faster and more accurately than identifying it. In all three tasks the number of distractors did not affect performance, i.e. the search was conducted in 'parallel', and performance decreased as target eccentricity increased. This eccentricity effect was more pronounced for the green than for the tilted target in all three tasks. Conclusion. A disjunctive target among heterogeneous distractors was detected faster than it was localized, which in turn was faster than it was identified. Target type affected performance in all three searches. We will discuss these results in light of current models of visual search.