Overview of the psychophysical technique
Subjects wore the contact lenses for approximately 25 minutes before beginning an experimental session with the tristimulus colorimeter. Before the start of the session, the experimenter demonstrated to the subject how turning the knob changed the color appearance of the test stimulus and explained that the goal was to identify “pure white” (or “snow white,” no identifiable tints or colors). The tester then moved the control knobs to achieve a maximal saturation starting point that participants reliably identified as “red.” From that point, the subject verbally guided the experimenter's adjustments until no hint of hue was perceived, with a criterion point of “pure white.” The same procedure (below) was repeated for maximal saturation starting points that participants reliably identified as red, green, and blue.