Hemispheric asymmetry for visual information processing in 3D space

There is an asymmetry in the ability to process visual information in the left and right visual fields. Extensive literature has consistently shown that young, healthy human adults exhibit a visuospatial bias towards the left hemifield (pseudoneglect). This leftward bias has traditionally been demonstrated through horizontal line bisection tasks in 2D experimental settings. However, as research progressed into 3D space, where lines are presented far from the observer, the dissipation of the classical leftward bias tended to reverse into a rightward bias. The precise distances at which the leftward bias, a neutral point, and rightward biases occur remain unclear. Here, we present a meta-analysis to model how bisection performance changes across 3D space quantitatively. We identified the boundary conditions where leftward biases reverse into rightward biases and at what distances this change can be predicted using line bisection. A total of 30 samples (25 studies, 142 bisection-error effects, n=720) were included. Overall, the analysis revealed a significant leftward bias within near space, followed by a rightward bias in far space. Three critical ranges for visuospatial asymmetries across depth were revealed in young, healthy adults: (1) significant leftward biases up to 48cm, (2) no reliable leftward/rightward biases from 49-87cm, and (3) significant rightward biases beyond 88cm. In addition, we revealed significant moderating effects of participant age (50+ years old), the use of tools to perform bisection, and the control of retinal size across depth. The findings establish important benchmarks when investigating visuospatial asymmetries and could inform clinical assessment.