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Shahina Pardhan, Angela Whitaker; Contrast and orientation dependence on binocular recognition summation in the periphery. Journal of Vision 2002;2(7):318. doi: https://doi.org/10.1167/2.7.318.
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Binocular and monocular spatial frequency thresholds for recognition were measured at two contrast levels (95% and 7%) and two orientations (vertical and horizontal). Measurements were obtained from 10 visually normal young subjects at the fovea and at 10 degrees superior field. Recognition threshold was defined as the highest spatial frequency at which luminance gratings were perceived veridically. Binocular summation ratios defined as binocular/monocular spatial frequency were calculated. In the fovea, no significant difference in binocular summation ratios for horizontal and vertical gratings at either contrast level was shown. Binocular summation ratios in the periphery were significantly dependent on the orientation of the gratings as well as the contrast level. Although the high contrast gratings showed no significant difference in binocular summation ratios between the centre and peripheral field, the vertical gratings at the lower contrast showed significantly higher binocular summation compared to the horizontal. Binocular summation for recognition increases at lower contrast and conforms to the radial organisation of the retina (i.e. vertical gratings are seen maximally in the superior field). These results indicate that radial organisation may take place nearer the fovea than previously thought and it may be possible to examine this with more sensitive stimuli.
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