Figure 1.

Graphic illustration of a canonical visual performance field (based on data from Carrasco et al., 2001). Each dot represents performance as a function of polar angle at a fixed eccentricity. The center of the polar plot corresponds to chance level, with highest performance typically observed along the horizontal meridian (HM; green), without differences between left and right hemifields. The horizontal-vertical anisotropy (HVA) depicts better performance in many tasks along the HM than the vertical meridian (VM). Moreover, performance is better at the lower VM (LVM; blue) than at the upper VM (UVM; purple), which is referred to as the vertical meridian asymmetry (VMA). Performance along the intercardinal (± 45°) meridians (gray) is usually similar, raising questions about the degree of visual performance fields as a function of polar angle.