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Masato Sakurai, Kathy T. Mullen; Peripheral chromatic sensitivity for rectified stimuli in each cone-opponent system. Journal of Vision 2005;5(8):1017. doi: 10.1167/5.8.1017.
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© ARVO (1962-2015); The Authors (2016-present)
Aims: To determine the presence of asymmetries in cone contrast sensitivity between the two poles of each of the L/M and S/L+M cone opponent systems across the human visual field.
Methods: We used chromatic rectified stimuli modulated in the following directions in cone contrast space: an isoluminant +L−M cardinal direction (red), an isoluminant +M−L direction (green), +S (blue) and −S (yellow). The stimulus was a spatial and temporal Gaussian ,gblob,h on a gray background (49.7 cd/m2, (x, y) = (0.275, 0.293)) with a fixed spatial sigma of 0.5 deg in the horizontal meridian, and a sigma in the vertical meridian that varied from 0.5 to 1.8 deg with eccentricity, determined by the magnification factor in V1. (Temporal sigma = 0.125 sec). Stimuli were presented from 0 to 20 deg in the nasal visual field in 5 deg steps. Cone contrast thresholds were measured using a standard 2AFC staircase procedure.
Results: The results show a much steeper decline in sensitivity of the L/M compared to the S-cone opponent system. The L/M system shows an asymmetry with ,green,h cone contrast sensitivity decreasing more than the ,gred,h at eccentricities over 10 deg. Little or no asymmetry is found in the S-cone opponent system.
Conclusions: Our results showing the asymmetry of cone contrast sensitivity in the L/M cone opponent system support those of Stromeyer et al., Vis. Res., 1992 and extend them to a wider range of conditions. They add to other evidence showing a rectification in the L/M cone opponent system. The lack of asymmetry found in the S-cone opponent system indicates that the underlying cause of the asymmetry is unique to the L/M cone opponent system.
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