Figure 5.

UV- green color exchange stimulus and hypothetical responses. A, Schematic showing stimulus conditions (top). Each stimulus contained a simultaneous 1 s step in UV and green luminance. One LED was always stepped to a 40% increment and the other LED color change could vary, creating ratios from −2.5 to 2.5. B, Hypothetical response to the above stimuli of an OFF cell that sums luminance linearly independently of wavelength. Responses are highest to luminance decrements, are similar for UV and green, and the null point is negative. C, Hypothetical green-OFF/UV-ON cell that displays color opponency. Responses are highest for green decrements and UV increments; the responses to each color diverge and the null point is positive.