(A) Pixel white noise stimulus (left), spike-triggered average (STA; right). Two sets of contiguous pixels were yoked to create two hyperpixels, each of which stimulated one RF subfield (white outlines). (B) Hyperpixel white noise stimulus (left) and STA at the peak frame (middle). Red, green, and blue curves (right) represent the average red, green, and blue phosphor intensities, relative to background, as a function of time before a spike. (C) A firing rate map for the example DO cell. The probability of spiking (grayscale) is plotted as a function of projection magnitudes of the hyperpixel stimulus onto the right and left halves of the STA (the 45° and 135° directions, respectively). Solid and dashed white lines are contours of constant spiking probability from GLM and GQM fits to the data, respectively. The firing rate map is binned to facilitate visualization, but models were fit to unbinned data. (D) Histogram of white noise NLIs for DO cells. The NLI of the example neuron is marked with a tick, and the median is marked with a triangle. (E) Same as (D) but for simple cells. (F) Same as (D) but for the other spatially opponent cells. DO, double-opponent; GLM, generalized linear model; GQM, generalized quadratic model; NLI, nonlinearity index; RF, receptive field.