A recent study of blind and sighted athletes has provided researchers with evidence supporting the idea that facial expressions are hard-wired(に組み込まれている)in the human brain. A review of 4,800 photographs capturing the expressions of sighted and blind judo athletes at medal ceremonies showed that both groups display and control their expressions in the same way. While both blind and sighted gold medal winners showed genuine joy, the silver medalists tended to produce "social smiles" - insincere smiles that use only the mouth muscles. Because people who are blind from birth cannot learn to produce social smiles through visual learning, the researchers have concluded that some innate mechanism must control these facial expressions.