All participants will wear tinted lenses for 1 hour at a time, 5 times per day. Perception (behavior) and neural function (with functional MRI and EEG) before and after this experience will be measured. In the neural measurements, activity will be recorded while participants view stripes of many different colors both with the lenses on and off. In the perceptual measurements, participants will adjust the color of a small patch to appear neutral, neither red nor green. Behavior will be measured in a variety of conditions to test different hypotheses about the origins of the mode-switching effects. These include: 1) surrounding the patch with different colors, 2) preceding the presentation of the patch with presentation of different colors, 3) presenting the tests in a red-illuminated room, 4) presenting the tests in a completely darkened room, and 5) using a head-mount-display (virtual reality goggles) to present simulated lenses that gradually change in strength.
