The prevailing view among scientists for how speech works in the human brain is that it's planned in advance -- consciously thought out -- and then executed, or spoken. But some cognitive scientists have suggested that speech is only partially planned, that part of our understanding of what we say comes from our hearing ourselves speak. In other words, speakers often don't truly know what they're saying until they've already said it. To test this theory, researchers at Lund University in Sweden outfitted study participants with noise canceling earphones and had them say one word while hearing another. "If we use auditory feedback to compare what we say with a well-specified intention, then any mismatch should be quickly detected," lead researcher Andreas Lind said. "But if the feedback is instead a powerful factor in a dynamic, interpretative process, then the manipulation could go undetected." They accomplished this manipulation by having participants identify colors, and recording their answers. As the test progressed, researchers were able to play back the answerers' own voice in their headsets. Words like "green" and "gray" were switched around. After each color identification question, the test subjects were given the chance to admit whether they had mistakenly said the wrong word. And then at the end of the testing, participants were asked whether they'd noticed the word switch. Two-thirds hadn't. And of those who didn't, 85 percent were tricked into thinking they'd said the wrong word. Barbara Davis, a speech expert at the University of Texas in Austin, told the journal Nature that she finds the work intriguing, but doesn't believe the results disprove speech pre-planning. "Naming a color is different than fluid discourse, it's a different level of complexity," Davis said. "A lot of people would agree that there is both pre-planning and auditory feedback going on." Lind agrees. He said auditory feedback is obviously not the only factor at work. If it was, deaf people wouldn't be able to speak. "If you don't have [auditory feedback] you can still speak," Lind pointed out. "But if you do have it, you probably rely on it more than other types of feedback when it comes to determining the meaning of your own words."