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Florian Bayer, David Weiss, Karl Gegenfurtner; Opposed interaction of rods and long-wavelength-sensitive cones under mesopic lighting conditions. Journal of Vision 2013;13(9):1011. doi: 10.1167/13.9.1011.
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Signals of rods and cones are combined within the retina already. While two retinal pathways of rod-cone interaction have been identified (reviewed by Sun, Pokorny & Smith, JOV 2001b), consequences on perception are not fully understood yet. We have assessed rod-cone interaction with Gaussian blobs flickering at 1 and 10 Hz. Stimuli were presented by an image display device consisting of two filtered LED-projectors whose beam projections were combined by a semitransparent mirror. By careful calibration using a PR-650 radiospectrometer this device allows independent stimulation of rods and short (S)-, middle (M)-, and long (L)-wavelength-sensitive cones within a contrast range of at least ±10%. The flickering Gaussian blobs (σ=0.2°) were presented at 5° eccentricity on a uniformly gray mesopic background at 4.6 cd/sqm. Four dark-adapted trichromats were examined using a 4-AFC task and the method of constant stimuli. In the first experiment thresholds for rods and cones were determined separately. In agreement with previous findings cone thresholds were higher at 10 Hz than thresholds measured at 1 Hz, whereas rod thresholds did not differ between frequencies (Hess & Nordby, J. Physiol. 1986). In the second experiment each cone flicker was interfered with a constant sub-threshold rod flicker. Thresholds of rod influenced M- and S-cones decreased for both frequencies, suggesting a summation of rod and cone signals. L-cones showed an opposing pattern of interaction with rods: thresholds dropped at 10 Hz as well but increased significantly at 1 Hz. So far, in-phase combination of rod and cone flicker has been reported to augment cone sensitivities (Buck. In: Chalupa, Werner, editors. The Visual Neurosciences. MIT; 2004. pp. 863-878). Our results show that this is not mandatory for L-cones at low frequencies.
Meeting abstract presented at VSS 2013
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