Hemispheric asymmetry for visual information processing in 3D space

The ability to process visual information is not the same 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 compared to the right hemifield (pseudoneglect). This leftward bias has traditionally been demonstrated through horizontal line bisection tasks by researchers in two-dimensional (2D) experimental setups. However, as line bisection research progressed into three-dimensional (3D) space, where lines are presented further 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. In particular, we identified the boundary conditions where patterns of leftward bias reverse into rightward biases and at what distances this change can be predicted using horizontal line bisection. A total of 30 samples from 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 48 cm, (2) no reliable leftward/rightward biases from 49–87 cm, and (3) significant rightward biases beyond 88 cm. 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, informing clinical assessment using line bisection.