The Short-Term Retention of Depth

Top-down modulation on depth processing: Visual searches for metric and ordinal depth information show a pattern of dissociation

Depending on the goal, one can selectively process the metric depth or the ordinal depth information in the same scene. It is unknown whether the metric depth and ordinal depth information are processed through a shared or different underlying mechanisms. Here, we investigated the processing of the metric depth and ordinal depth using visual search. Items were presented at multiple depth planes defined by the binocular disparity, with one item per depth plane. In the metric-search task, participants were required to search for the target on a particular depth plane, among one to three distractors. In the ordinal-search task, the target was specified by its depth order indicated by numbers (smaller numbers indicated nearer depth planes). We found that the ordinal search was faster and more accurate than the metric search, and the data showed a pattern of dissociation. Metric search, but not ordinal search, was slowed when the target and distractors were closer in depth, while ordinal search was slower for the middle than the edge positions but metric search was unaffected. These two opposite effects suggest that metric depth and ordinal depth may be processed differently.

Spatial attention based on 2D location and relative depth order modulates visual working memory in a 3D environment

The attentional effect on visual working memory (VWM) has been a heated research topic in the past two decades. Studies show that VWM performance for an attended memory item can be improved by cueing its two-dimensional (2D) spatial location during retention. However, few studies have investigated the effect of attentional selection on VWM in a three-dimensional setting, and it remains unknown whether depth information can produce beneficial attentional effects on 2D visual representations similar to 2D spatial information. Here we conducted four experiments, displaying memory items at various stereoscopic depth planes, and examined the retro-cue effects of four types of cues - a cue would either indicate the 2D or depth location of a memory item, and either in the form of physical (directly pointing to a location) or symbolic (numerically mapping onto a location) cues. We found that retro-cue benefits were only observed for cues directly pointing to a 2D location, whereas a null effect was observed for cues directly pointing to a depth location. However, there was a retro-cue effect when cueing the relative depth order, though the effect was weaker than that for cueing the 2D location. The selective effect on VWM based on 2D spatial attention is different from depth-based attention, and the divergence suggests that an object representation is primarily bound with its 2D spatial location, weakly bound with its depth order but not with its metric depth location. This indicates that attentional selection based on memory for depth, particularly metric depth, is ineffective.