Effect of different directions of attentional shift on inhibition of return in three-dimensional space

When attention is oriented to a peripheral cue, the processing of nearby stimuli is facilitated. This brief period of facilitation is followed by a long-lasting inhibitory effect, during which there is a delayed response to stimuli presented at a previously cued location. Although the mechanisms underlying the facilitatory effect of attentional orienting/reorienting in three-dimensional (3-D) space have been documented, there is not yet consensus as to how attention orients/reorients in depth during the later inhibitory phase (i.e., inhibition of return [IOR]). In the present study, by incorporating the Posner exogenous cueing paradigm into a virtual 3-D environment, we aimed to investigate whether an IOR effect occurs when attention orients and reorients at the uncued depth in the same hemispace, and whether the IOR effects are the same or different when attention orients/reorients along different trajectories in 3-D space. Our results showed asymmetrical spatial IOR effects when attention was oriented/reoriented at the uncued depth in the same hemispace. Spatial IOR was depth-specific when targets appeared in the near depth plane, whereas it was not depth-specific when targets appeared in the far depth plane. Apart from these results, we also found that attention oriented/reoriented at the same depth but in a different hemispace experienced a reduction in IOR size, thus indicating that the direction-specific spatial IOR mechanisms when attention orients/reorients along different trajectories are different. Taken together, our results suggest that spatial IOR is not entirely "depth-blind," and that the ecological importance of the 3-D world influences the direction of attentional shifts of spatial IOR in 3-D space.