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TK Kuyk, P Fuhr, E McIntosh, D Cope; The Human Periphery Effect Along the Vertical Meridian . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2838.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In the periphery effect (PE), thresholds for some visual stimuli are elevated by modulating the luminance of retinal areas that are far removed from the target locus. In a previous study we demonstrated the PE crosses over the vertical meridian (VM) near the fovea. In the present study we asked if the PE also crosses the VM in peripheral retina. Methods: Three observers set increment thresholds for large (1.5 deg.), brief (8 ms) achromatic or red spots. The spots were offset 1.75 degs. to the left of the VM and centered either on the horizontal meridian or 4 or 8 degs. above it. The test spot was presented on a 41 cd/m2 white background. The spot and background were either surrounded by an achromatic field that extended on both sides of the VM (no grating condition), by a homogenous field to the left and a counter-phased grating to the right of the VM (grating & test opposite side), or by the reverse (grating & test same side). Results:Sensitivity to the test spots declined with increasing vertical eccentricity. At all retinal locations tested, with the spot and grating on opposite sides of the VM, small but significant elevations of test threshold (approx. 0.1 log unit) were found compared to the no grating condition. When the grating was presented on the same side of the VM as the test, PE magnitude approximately doubled to 0.2 log units. For the achromatic target, both the same side and crossover PE were constant in magnitude as a function of eccentricity, but for the red target both increased between 4 and 8 degrees. Conclusion:The PE crosses the VM in both central and peripheral retina. However, the crossover PE is reduced in size by approximately 40% compared to when the grating and test are presented on the same side of the VM. This suggests there may be a difference in how the neural mechanism that transmits the PE signal laterally across retina is organized for sending the PE signal across the VM as compared to within a retinal hemifield.
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