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J. J. Kremers, N. K. Challa, N. R. A. Parry, I. J. Murray, A. Panorgias, D. McKeefry; L- and M-Cone Input to Opponent and Non-Opponent Channels as a Function of Retinal Eccentricity in the Human Erg. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1502.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the retinal eccentricity dependency of L- and M-cone inputs to the cone opponent and non-opponent post-receptoral mechanisms in human observers with flicker ERGs.
ERGs were obtained from a series of flickering stimuli (either 30Hz or 12Hz previously found to reflect activity of the non-opponent and the L-/M-cone opponent channels respectively, Kremers & Link, J Vis 8, 1-14) using the following spatial configurations: (1) Circular stimuli of different angular subtense which increased in 10° steps up to 70° diameter. (2) Annuli with 70° outer diameter and gradually ablated from the centre in 10° steps. Responses to L- and M-cone isolating stimuli with equal cone contrasts were obtained from colour normal subjects using a DTL electrode. The amplitudes and phases of the first harmonic components were obtained.
The ratio of the L- and M-cone response amplitudes was found to be at or close to unity at 12Hz for central as well as peripheral stimuli and the L- and M-cone phase differences were close to 180o compared to the smaller phase differences measured for the 30Hz responses. At 30Hz the L-/M-cone ratio was found to vary from 4:1 to 10:1, for different observers. Those observers with small M-cone driven responses displayed larger L-/M- ratios with a large stimulus size compared with the small central and the far peripheral annular stimuli. In these subjects, the phases of the M-cone driven responses differed strongly for the central and peripheral stimuli.
The L-/M-cone-opponent post-receptoral mechanism seems to maintain its cone selective input in the peripheral human retina. In subjects with particularly small numbers of M-cones, the M-cone driven response in the non-opponent channel may have strongly different phases in central and peripheral retina which may cancel each other out when stimulated simultaneously leading to particularly large L-/M-ratios in when using large stimuli.
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