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H. Sun, H. Smithson, B. Lee, Q. Zaidi; A new technique for measuring cone inputs to visual neurons . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4277.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A new technique is described to measure the magnitudes and signs of cone inputs to visual neurons; data from macaque ganglion cells are used to illustrate the method. Methods: The signs and relative weights of the cone inputs to a cell determine its preferred vector in a 3D cone–excitation space. If the color of a uniform field is modulated around the circumference of a circle in a plane of cone–excitation space, each cell’s response phase is equal to the angle of the cell’s preferred vector plus a phase lag intrinsic to the cell. The cell’s preferred vector remains the same whether the direction of modulation is clockwise or counterclockwise along the circumference, but the intrinsic phase lag changes its sign from clockwise to counterclockwise modulation. Averaging response phases to clockwise and counterclockwise modulation cancels the intrinsic phase delay to reveal the cell's preferred vector. Cells’ responses were measured for stimuli modulated in the equiluminant plane, a plane defined by L– and M–cone axes and a plane defined by L+M and S–cone axes. Temporal frequency was varied between 1.22 and 39.4 Hz. Results: We estimated the preferred vector of M–, L–cone opponent parvocellular ganglion cells at different S–cone adaptation levels and found small S–cone inputs to a small percentage of cells. For magnocellular ganglion cells, more complex properties are present due to a L–M chromatic nonlinearity. However, measurements in an S vs (L+M) plane show little evidence of S–cone input. Conclusions: The method reliably measures preferred vectors, and hence, signs and weights of cone inputs to visual neurons. The method is quick and sensitive compared to methods based on measurements of response amplitude.
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