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S-I Tsujimura, WH Swanson; Measurement of Phase Shifts Between L and M Cones at Several Eccentricities Parallels the Size of the Receptive Field of Magno-cellular Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3789.
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Purpose: Psychophysical and physiological studies have shown substantial phase shifts between L- and M-cone signals in magnocellular pathway (1,2). Smith et al. (1992) suggested that the phase shifts can reflect the size of the receptive field of magnocellular ganglion cells. The aim of this study was to measure the phase shift as a function of spatial frequency to determine whether effect of eccentricity on the relationship between spatial frequency and phase shift parallels the effect of eccentricity on the size of the receptive field of magnocellular ganglion cells. Methods: We used an optimized technique (3) to estimate the phase shifts between L- and M- cone signals at several spatio-temporal frequencies (TF: 10 Hz, SF: 0.25, 0.5, 1.0 and 2.0 c/deg) and eccentricities (0, 10, and 20 deg, nasal). We measured motion identification thresholds for a drifting sinusoidal grating modulated along two vector directions in cone-contrast space with four relative physical phases between L- and M- cone signals. Each phase shift was estimated from these eight thresholds. We used an orange background with a luminance of 34 cd/m2. Results: At each eccentricity the magnitude of phase shift markedly decreased as spatial frequency increased. At each spatial frequency phase shifts decreased as eccentricity increased. When spatial frequency was scaled to the dendritic field size of magnocellular ganglion cells (4), phase shifts became relatively independent of eccentricity. Conclusion: The effects of eccentricity on phase shifts can be accounted for by scaling the spatial frequency with magno-cellular dendritic field size. Refferences: 1) V. C. Smith, B. B. Lee, J. Pokorny, P. R. Martin, and A. Valberg, J. Physiol. 458, 191-221, (1992) 2) C. F. Stromeyer III, A. Chaparro, A. S. Tolias, and R. E. Kronauer, J. Physiol. 499, 227-254, (1997) 3) S. Tsujimura, S. Shioiri, Y. Hirai and H. Yaguchi, J. Opt. Soc. Am. A, Vol.17, 846-857, (2000) 4) D. M. Dacey and M. R. Petersen, Proc. Natl. Acad. Sci. USA, Vol. 89, 9666-9670, (1992)
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