They made 45 errors when doing it silently. But that fell to just ten when the same people thought out loud, describing what they were doing and their thinking process.
Study author Christopher Atkin, who presented his findings at the annual conference of the British Psychological Society, said: "These findings can be explained by the clarity which overtly vocalising an activity, or 'thinking aloud', can bring. When people internalise their thoughts, there can be competing thoughts which try to break through.
"Thinking aloud and saying the words focuses your attention, it focuses your concentration."
Speaking at the conference in Nottingham, Mr Atkin added: "People can see talking to yourself as something slightly unacceptable. But for a problem which requires cognitive flexibility, this approach seems to work.
"The same approach might be useful for puzzles like sudoku or crosswords, for building furniture or finding the way in a car."