Abstract
Inhibition of return (IOR) is a phenomenon where responses to a peripheral target are delayed if the target appears more than 300ms after a cue, when the cue appears in the same peripheral location compared to a cue appearing in the opposite side of central fixation. IOR has been extensively shown to operate in 2D scenes. However, it is not fully understood whether IOR is determined by relative location between cue and target in retinal coordinates or world coordinates. Such a question can be studied by examining IOR in 3D scenes. We compared IOR when cues and targets appeared at same or different depth planes and when depth information was provided by monocular cues (mostly linear perspective) presented on a projection screen. In the 3D condition, cue and target (of identical retinal size) appeared atop of placeholders that intersected with a ground plane. When the cue and target appeared at different depths, a vertical offset was created on-screen, which was a potential confound to depth perception. We removed the contribution of this confound by contrasting the 3D condition with a 2D control condition that matched cue and target positions but removed all context simulating 3D space. Results showed that the magnitude of IOR decreased for the different-depth condition compared to the same-depth condition in 3D displays. The magnitude of IOR also decreased as a function of vertical offset in corresponding 2D displays. Most importantly, such magnitude reduction in 3D displays was higher than that in the corresponding 2D displays, but only when the difference in depth was caused by the target appearing at a nearer position (closer to the viewpoint) compared to the cue. We thus have identified a depth-specific IOR effect, which occurs only when attention shifts from far to near space relative to the viewer.