Polar angle asymmetries persist despite covert spatial attention and differential adaptation

Visual adaptation and attention are two processes that help manage brain limited bioenergetic resources for perception. Visual perception is heterogeneous around the visual field, it is better along the horizontal than the vertical meridian (horizontal-vertical anisotropy, HVA), and better along the lower than the upper vertical meridian (vertical meridian asymmetry, VMA). A recent study showed that visual adaptation is more pronounced at the horizontal than the vertical meridian, but whether and how the differential adaptation modulates the effects of covert spatial attention remains unknown. In this study, we examined how the effects of endogenous (voluntary) and exogenous (involuntary) covert attention on an orientation discrimination task vary at the cardinal meridians, with and without adaptation. We manipulated endogenous (Experiment 1) or exogenous (Experiment 2) attention via a central or peripheral cue, respectively. Results showed that (1) in the non-adapted condition, the typical HVA and VMA emerged in contrast threshold; (2) the adaptation effect was stronger at the horizontal than the vertical meridian; and (3) regardless of adaptation, both endogenous and exogenous attention enhanced and impaired performance at the attended and unattended locations, respectively, to a similar degree at both cardinal meridians. These findings reveal that, despite a differential adaptation effect, performance asymmetries are resistant to both endogenous and exogenous attention around polar angle.