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Shutian Xue, Antoine Barbot, Marisa Carrasco; Spatial frequency asymmetries around the visual field. Journal of Vision 2020;20(11):116. doi: https://doi.org/10.1167/jov.20.11.116.
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[Goal] At a given eccentricity, performance 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). These performance fields are present in numerous visual tasks, including those mediated by spatial resolution. Here we investigated the extent of these spatial resolution asymmetries by measuring the HVA and VMA for spatial frequency (SF) sensitivity at different polar angles. Furthermore, to investigate the possible contribution of binocular disparity in performance fields, we assessed SF sensitivity both monocularly and binocularly.
[Methods] We measured SF sensitivity at 24 isoeccentric (10º) locations. In each trial, four grating stimuli oriented ±45º appeared each at 4 locations separated by 90º polar angle. Observers reported the orientation of the target stimulus indicated by the response cue. The axis of the four isoeccentric locations was rotated across blocks to assess SF sensitivity every 15º polar angle. We obtained SF thresholds and cutoff points for each location and compared them under monocular and binocular viewing conditions.
[Results] Lower SF thresholds and cutoff points were found in the lower than the upper visual hemifield. The extent of both HVA and VMA decreased linearly as the angular distance from the vertical meridian increased. This pattern of results was similar for binocular and monocular viewing conditions.
[Conclusions] The HVA and VMA in SF sensitivity are most pronounced at the vertical meridian and decrease gradually, being no longer significant by the intercardinal meridia. Similar performance fields under monocular and binocular viewing conditions rule out differences in binocular disparity as a possible explanation. Consistent with findings showing a gradual decrease of these asymmetries for contrast sensitivity (Abrams, Nizam & Carrasco, 2012), our results indicate that comprehensive models of visual perception need to take into account the existence of performance fields.
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