Comparing eye movements to detected vs. undetected target stimuli in an Identity Search task.

Why do we perceive some elements in a visual scene, while others remain undetected? To learn about the sequence of events leading to detection, we directly compared fixations on detected vs. undetected items. Our novel Identity Search task display comprised twelve cards, all different except for two pairs of identical cards. Participants search for one pair. Task properties allow us to monitor fixations on distinct card regions and study search dynamics. We find that detected pair cards were fixated more often and for longer times than undetected pair cards. Within the search sequence, there are fewer intervening fixations between detected than undetected pair cards. Only at an advanced stage of the search do fixations on pair cards become closer. We suggest that both the absolute number of fixations and their temporal proximity influence detection. In the dynamics of search, a bifurcation point is observed, when these differential characteristics begin. Analysis of the break point in the sequence of fixations on to-be-detected cards suggests that there is an early--perhaps unconscious--recognition stage, followed by more fixations and only later by detection. We suggest that several target fixations are needed for processing visual information to achieve recognition.