For decades, economists have tried to guess central bank policy direction by studying subtle changes in official language -- now, researchers are finding new clues on policy, not in the words of central bankers but in their faces. In Japan, two artificial intelligence researchers, one from Nomura Securities and the other from Microsoft, are using software to analyze split-second changes in the facial expressions of Bank of Japan Gov. Haruhiko Kuroda at his post-meeting news conferences. Their study found that Kuroda showed fleeting signs of "anger" and "disgust" at news conferences that preceded two recent major policy changes -- the January 2016 introduction of negative interest rates and the adoption of the so-called yield curve control policy in September last year. The implication is that Kuroda was beginning to sense the constraints of existing policies about six or seven weeks before the central bank's board actually decided to change them, the researchers concluded. The research was presented last weekend to a subcommittee meeting of the Japanese Society for Artificial Intelligence (JSAI).