Monocular Cue Sensitivity Across Spatial Dimensions: A VR-Based Investigation of Depth and Vertical Distance Perception

Monocular vision provides essential spatial information when binocular input is unavailable, yet systematic research on its underlying mechanisms remains limited. This study quantified sensitivity to distance under four monocular cue contexts—linear perspective, relative size, light and shadow, and sparse scenes—across viewing distances of 0.4–1.2 m in depth (Z-axis) and vertical (Y-axis) dimensions using a controlled VR paradigm. Nineteen adults made monocular judgments with one eye physically occluded. Results revealed a pronounced dimensional dissociation: depth distance was heavily compressed (perceived/actual ≈ 0.28) while vertical distance was only mildly compressed (≈0.84, 3-fold gap, p < 0.001). No significant differences in compression were detected across the four cue contexts. The centered and scaled errors showed a shared distance-dependent pattern of deviations from participants’ mean perceived baselines, with positive values at nearer target depths and negative values at farther depths. These findings are consistent with the Intrinsic Constraint (IC) theory and describe a dimensional difference in distance scaling, with no significant differences detected among the tested cue contexts. Beyond theoretical implications, this work informs cue-based rehabilitation for monocular patients and the optimization of VR environments where binocular information is limited.