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Shutian Xue, Antoine Barbot, Marisa Carrasco; The extent of the vertical meridian asymmetry in spatial frequency sensitivity. Journal of Vision 2019;19(10):121c. doi: https://doi.org/10.1167/19.10.121c.
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© ARVO (1962-2015); The Authors (2016-present)
Goal: Human visual performance is heterogeneous across the visual field. At a fixed eccentricity, performance is better along the horizontal than the vertical meridian and along the lower than the upper vertical meridian. These performance fields are found in numerous tasks, including contrast sensitivity and spatial resolution. However, it is unknown whether the spatial resolution asymmetry is confined to the vertical meridian or whether and how far it extends into the upper and lower hemifields. Here, we measure the extent of this vertical meridian asymmetry by assessing spatial frequency (SF) sensitivity. Method: Spatial frequency sensitivity was measured using suprathreshold (100% contrast) gratings presented at isoeccentric locations (10°). In each trial, stimuli appeared at 4 locations separated by 90° polar angle. Participants were asked to discriminate the orientation (±45°) of the stimulus at the location indicated by a response cue. Auditory feedback was provided. In each block, the axes of the four isoeccentric locations were rotated clockwise from the vertical meridian by 0, 15, 30, 45, 60, 75 or 90° polar angle. The extent of the vertical meridian asymmetry was assessed by comparing 75%-correct SF thresholds for upper and lower visual field locations as a function of polar angle. Results: At constant eccentricity, SF sensitivity was higher in the lower than the upper visual hemifield, and was similar in the left and right hemifields. Moreover, we found that the vertical asymmetry in SF sensitivity decreased as the angular distance from the horizontal meridian increased, and was no longer significant by ~45° from the vertical axis. Conclusion: Our results imply that vertical asymmetry in SF sensitivity is most pronounced at the vertical axis and decreases gradually, being no longer significant by the secondary meridian. These results advance our understanding of performance fields and visual information processing, and constrain models of visual perception.
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