Allocation of attention in 3D space is adaptively modulated by relative position of target and distractor stimuli

Allocation of attention across different depth planes is a prerequisite for visual selection in a three-dimensional environment. Previous research showed that participants successfully used stereoscopic depth information to focus their attention. This, however, does not mean that salient information from other depth planes is completely neglected. The present study investigated the question of whether competing visual information is differentially processed when displayed in a single depth plane or across two different depth planes. Moreover, it was of interest whether potential effects were further modulated by the items' relative spatial position (near or far). In three experiments participants performed a variant of the additional singleton paradigm. Targets were defined by stereoscopic depth information and as such appeared either in a near or far depth plane. Distractor stimuli were displayed in the same or in the opposed depth plane. The results consistently showed that visual selection was slower when target and distractor coincided within the same depth plane. There was no general advantage for targets presented in near or far depth planes. However, differential effects of target depth plane and the target-distractor relation were observed. Selection of near targets was more affected by distractors within the same depth plane while far targets were identified more slowly when the amount of information in closer depth planes increased. While attentional resources could not be exclusively centered to a distinct depth plane, the allocation of attention might be organized along an egocentric gradient through space and varies with the organization of the visual surrounding.