Ordinal Information, but Not Metric Information, Matters in Binding Feature With Depth Location in Three-Dimensional Contexts

A basic function of human visual perception is the ability to recognize and locate objects in the environment. It has been shown that two-dimensional (2D) location can reliably bias judgments on object identity (spatial congruency bias; Golomb et al., 2014), suggesting that 2D location information is automatically bound with object features to induce such a bias. Although the binding problem of feature and location has been vigorously studied under various 2D settings, it remains unclear how depth location can be bound with object features in a three-dimensional (3D) setting. Here we conducted five experiments in various 3D contexts using the congruency bias paradigm, and found that changes of object's depth location could influence perceptual judgments on object features differently depending on whether its relative depth order with respect to others changed or not. Experiments 1 and 2 showed that the judgments on an object's color could be affected by changes in its ordinal depth, but not by changes in its absolute metric depth. Experiment 3 showed that the bias was asymmetric-changes in an object's color did bias the judgments on metric-depth location, but not if its depth order had changed. Experiments 4 and 5 investigated whether these findings could be generalized to a peripersonal near space and a large-scale far space, respectively, using more ecological virtual environments. Our findings suggest that ordinal depth plays a special role in feature-location binding: an object may be automatically bound with its relative depth relation, but not with its absolute metric-depth location. Public Significance StatementThis study explores how the way we perceive object features (such as color and shape) can be influenced by where they are located in three-dimensional space. Using both conventional stereoscopic lab settings and realistic virtual environments, our findings highlight that changes in object's relative depth, rather than its exact metric-depth location, can bias the perceptual judgment of object features. The differential biasing effects suggest that when we view objects in three-dimensional settings, their position relative to other objects may implicitly affect how we identify them, emphasizing the importance of ordinal-depth information in feature-location binding and object identification.