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Tobias Borra; Binocular orientation perception: the oblique effect occurs after binocular fusion. Journal of Vision 2007;7(9):818. doi: 10.1167/7.9.818.
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© ARVO (1962-2015); The Authors (2016-present)
Meng and Qian (2005) have suggested that the oblique effect (the more precise perception of horizontal/vertical orientations compared to oblique orientations) is determined by the perceived orientation of a grating. Here, we make the distinction between retinal and perceived orientation after binocular fusion. The horizontal separation of the two eyes, make it possible to disentangle retinal orientation and perceived orientation. Using a mirror-stereoscope, observers were presented with a temporally separated dichoptic reference and test stimulus. They were instructed to adjust the orientation of the test stimulus to the reference stimulus. Three reference stimulus orientations were used: 1] 0° (presented to both eyes); 2] −8° (both eyes) and 3] −8° (left eye) and 8° (right eye). This led to the following perceived orientations, 0°, −8° and 0° respectively. We calculated the standard deviations (SDs) of the differences between the reference and the adjusted test stimulus. If the oblique effect is determined by the orientation of the retinal object image, we expect small SDs for condition 1 and large SDs for both conditions 2 and 3. However, if the oblique effect is determined by the orientation of the object representation after binocular fusion, that is the perceived orientation, we expect small SDs for conditions 1 and 3, and large SDs for condition 2.
We found that the SD for condition 3 was significantly smaller than for condition 2. This suggests that the oblique effect is primarily determined by the orientation of an object after binocular fusion, that is, the perceived orientation, and not the retinal orientation of the stimulus.
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