I'm not sure what you mean. There is no reason to separate the stutterers to study stuttering; That seems to be BS, pretending to be an expert. I have repetitions, and I have times when there is no sound, and other things too: It's all stuttering. I don't know where you get your definitions from: stammer, blockers... Stutters would do all of the above at one point or the other even though the severity would differ. One group were stutterers, one group were non-stutterers. There was a contrast in the results between the groups. It was a good method of showing the difference. From there, anyone can do another study. But making declarations does not compete with a real study with a scientific method. The hypothesis seems to be that there is a different in the brain. And that was found to be true.