If European Central Bank chief Mario Draghi appears slightly more downbeat at his regular news conference than before, it could foreshadow a possible move by the bank to trim its monetary policy stimulus.

That's the conclusion of two Japanese researchers who have used artificial intelligence software to analyze split-second changes in Draghi's facial expressions at his news conferences following policy meetings.

The findings follow a similar analysis by the same researchers of Draghi's Japanese counterpart, Haruhiko Kuroda, last year, which claimed to have identified a correlation between patterns in his facial expressions and subsequent policy changes.