Number : VR-2047 Title : Color scrambles reveal Red and Green half-axis mechanisms plus a Gray-tuned mechanism Article Type : Full Length Article Keywords : Histogram contrast analysis ; Texture discrimination ; Color mechanisms Corresponding

In this paper we set up to enumerate and characterize mechanisms sensitive to color scrambles. A color scramble is a texture made of a finite number of elements drawn from a set Ω, in this case small colored squares, distributed according to a histogram. We use a novel method to derive a eight equiluminant lights along the Red-Green cardinal axis. We then generate a background annulus and a target disk to be detected in one of eight pre-defined locations. We modeled the mechanisms available to the subjects to do the task using the seedexpansion weighting procedure. This theory-free, datadriven approach, constrained only by the size of the set Ω, makes no assumptions about the number of mechanism used to perform the task, or about what they are sensitive to. We found that a model of three mechanisms explains well the data: one half-wave rectified mechanism sensitive to green, one half-wave rectified mechanism sensitive to red, and a mechanism sensitive to gray. We discuss the implications of this result. Dear Editor of Vision Research, On behalf of the authors Christian Herrera, Charles Chubb, Charles E. Wright, Peng Sun and George Sperling, I am submitting the manuscript titled: “Color scrambles reveal Red and Green half-axis mechanisms plus a Gray-tuned mechanism” to be included in the journal Vision Research. The authorship is to be kept in the order given above. The article presents original research, briefly summarized in the next few sentences. Using eight equiluminant lights that varied in saturation along the red-green axis, we created two textures to be used in a detection task, which was to find a disk made of one in a background annulus made of the other. Textures were made of small squares that could take any of eight values (any of the eight equiluminant lights), but following some restrictions, considered next. The proportion in which each light was used varied on each of the four conditions. On condition one the composition of the target disk texture followed a first-degree polynomial (a positive slope), while the composition of the background followed a negative slope. On condition two we reversed the composition of target and background. For condition three the composition of the target disk followed a seconddegree polynomial (a positive parabola), while the composition of the background followed a negative parabola. For condition four, again we reversed the composition of target and background. On each trial, we slightly varied, or perturbed, the exact composition of the histogram, although keeping a high correlation with the original, or “seed” histogram. Such perturbations let us model the relative weight that the participant applies to each of the eight lights to do the tasks. We then use these psychophysical data to characterize the mechanisms that the participant must use in order to do the task. We propose that participants use three mechanisms, one tuned to red and insensitive to green, one tuned to green and insensitive to red, and one tuned to grey. We hope you find merit in this manuscript, and consider it for publication in the journal Vision Research.