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Leslie Cameron, Michael Levine, Jennifer Anderson; Exploring the vertical meridian asymmetry: Is poor performance restricted to the vertical meridian?. Journal of Vision 2015;15(12):110. doi: 10.1167/15.12.110.
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© ARVO (1962-2015); The Authors (2016-present)
The vertical meridian asymmetry (VMA) refers to better performance below (“south”; S) than above (“north”; N) the point of fixation on the vertical meridian. Here we explore whether poor performance is restricted to the vertical meridian by testing a greater range of stimulus locations, particularly near the vertical meridian, than previous studies. Methods: We measured percent correct on a 2AFC orientation discrimination task of 8cpd Gabor patches presented at each of 36 locations, primarily concentrated within 30 deg. of the vertical meridian at about 4.5 deg. eccentricity. Target contrast was chosen for each observer in pilot threshold tests. Visual performance fields were fit with ellipses, which were constrained by performance at all locations except for the vertical meridian. The ellipse method is advantageous because it takes into consideration other well-known inhomogeneities (see Anderson et al., 2014). We computed difference scores (predicted percent correct based on the ellipse fit minus observed percent correct, at each location) and examined how the difference scores varied as a function of angular degree. Results: In the upper visual field difference scores were largest at the N location and were diminished as stimuli were placed further from the vertical meridian. The greatest effect was observed within 20 angular degrees on either side of the vertical meridian. In the lower visual field difference scores were relatively constant; performance was only marginally lower at the S location but the data were reasonably well fit by an ellipse. Conclusion: Although performance is known to be poorer in the upper visual field compared to the lower visual field, it is particularly poor within 20 deg. of the vertical meridian. This has implications for both vision research and the optimal design of visual displays.
Meeting abstract presented at VSS 2015
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