Performance differences around polar angle vary systematically across experimental conditions

[Background] Visual performance varies at isoeccentric location around polar angles–it is better along the horizontal than vertical meridian (horizontal-vertical anisotropy, HVA) and at the lower than upper vertical meridian (vertical meridian asymmetry, VMA). Here, we examined whether the magnitude of these two asymmetries (1) differ from and (2) correlate with each other across multiple published studies. [Method] We calculated the magnitude of HVA and VMA across multiple studies using an orientation discrimination task, which varied in stimulus properties (e.g., eccentricity, stimulus size and degree of tilt) and reported measurements (e.g., contrast sensitivity and acuity). First, we assessed whether they alter the magnitude of HVA and VMA. Second, we assessed the correlation between the magnitude of HVA and VMA while controlling for stimulus properties and measurement. [Results] (1) HVA is stronger than VMA across stimulus properties (eccentricity and stimulus size), especially for contrast sensitivity-related measurements. (2) The extent of the HVA did not correlate with that of the VMA while controlling for stimulus properties and measurements. [Conclusion] Despite the variability in how performance for fundamental visual dimensions vary around polar angle across studies, an analysis across multiple studies shows that (1) HVA is more robust than VMA for some measures (e.g., contrast sensitivity). (2) HVA did not correlate with VMA. Results suggest that these two visual field asymmetries may derive from distinct neural computations