Even so, the scientists found that people were able to recognize more than 80 percent of what they’d seen. In a more recent study, the same test was performed with 2,500 images, but instead of asking people to choose between an image of Muhammad Ali and an Alka-Seltzer tablet (an easy choice, no matter how effervescent Cassius Clay might have been), they had to choose between alternative images that were almost identical: a stack of five dollar bills versus a stack of one dollar bills, a green train car versus a red train car, a bell with a narrow handle versus a bell with a wide handle. Even
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