Abstract
[Goal] At a fixed eccentricity, contrast sensitivity is higher along the lower than upper vertical meridian. This asymmetry is exacerbated at high spatial frequencies (SF) and eccentricities. Exogenous and endogenous spatial attention--respectively, involuntary and voluntary selection of spatial locations without eye movements--differentially modulate contrast sensitivity across SF along the horizontal meridian. Here, we investigated whether and how their differential modulation generalizes to the vertical meridian. We measured the effects of exogenous and endogenous attention on contrast sensitivity along the vertical meridian and across SF and eccentricity within the same observers. [Methods] Observers performed a 2AFC orientation discrimination task. Tilted (±45°) gratings were displayed along the vertical meridian above and below a fixation cross. In Valid conditions, peripheral precues manipulated exogenous attention and central precues manipulated endogenous attention. In Neutral conditions, non-informative precues distributed attention across the vertical meridian. Response cues indicated the target. Four gratings were displayed with one of eight SFs (0.5-11 cpd) and simultaneously at two eccentricities (2°, 6°). On each trial, gratings had the same SF and their contrasts were fixed (based on initial threshold sessions) such that Neutral performance was titrated to a d′ of 1.5 across SF and eccentricity. [Results] Contrast sensitivity was higher along the lower than upper vertical meridian, bandpass across SF and declined with eccentricity. Neutral performance was equated across SF, eccentricity and meridian location (upper, lower). Exogenous attention preferentially enhanced SFs higher than those intrinsically preferred in the Neutral condition at each eccentricity. In contrast, endogenous attention improved SFs both higher and lower than baseline preferences. Each type of attention operated similarly at lower and upper vertical meridians. [Conclusion] Our results provide converging evidence that covert attention differentially shapes spatial frequency sensitivity across and around the visual field, but cannot overcome the asymmetries.