Finding “white”
From each of these three starting points, the experimenter systematically adjusted one axis (e.g., red–green) at a time and instructed the subject to state when the visual field was as close to white as possible along that axis, at which point the experimenter stopped turning that dial. Then, the experimenter moved to the other axis (red–green–blue in this example) and adjusted that dial until the visual field was as close to white as possible. This continued, back and forth, with small, fine-tuned adjustments, until the subject reported that the visual field was pure white without any tint of color.When an approximate white setting was obtained, subjects were asked to look away from the device for approximately 5 seconds, and then back into the eye piece to double check that the visual field did not contain any tint of color at that setting. They were asked such questions as, “If you had to give what you are seeing a color name, what would you call it?” Also, using that setting, the experimenter turned each knob to bracket the area (meaning, at the point where the subject first perceived a tint). Four trials, one from each starting point, were collected for each eye. For each measurement, the spectroradiometer provided measures of the stimulus color as in chromaticity coordinates (