Baseball and football players have claimed for decades that swiping black grease under their eyes helps them peer into a sunny sky to catch a ball. In recent years, the smudges have given way to tidier patches of black tape.
Brian DeBroff and his colleagues at Yale University School of Medicine now report that the black grease really does work–but that the newfangled black-tape patches don't stand up to the light of day.
The researchers used a standard test to assess how well 46 students could discern contrast against a sunlit background. Then the scientists randomly assigned the students to wear black grease, tape patches, or clear petroleum jelly. When retested, students sporting the black grease showed significant improvement in discerning contrast, whereas the other two groups didn't.