Luminance contrast and the visual span during visual target localization

A concern for designers of monocular and binocular devices is the ability of users to search for, and localize target items embedded in noisy displays. Twenty-two participants searched (12 under monocular conditions) to localize a target embedded in random gray dot displays. The target was defined by a variation in pattern that did not differ in average contrast from the rest of each display. Displays were presented at .54 and .04 Michelson contrast. Across binocular and monocular viewings, fixation counts increased with decreasing contrast, but the gradient was steeper for monocular viewing. With decreasing contrast, fixations were longer, and the amplitudes of saccades used to localize the target decreased. The findings highlight for monocular vs. binocular target localization, the importance of considering separately, how many fixations are needed to localize the target, and how close to fixation the target must be for it to be noticed.

► Fixation durations were longer under lower luminance contrast. ► Fixation counts were higher under lower luminance contrast. ► Saccade amplitudes are a useful spatial metric during visual processing. ► Target localizing saccade amplitudes were shorter under lower contrast. ► Target localizing saccade amplitudes are a window on visual span size.