People actually working with communication disorders have always known this. You don't need a study. How about talking to professionals that know what they are doing and have amazing results which is not "spontaneous recovery " that the brilliant MDs like to throw around. I am a Speech Language Pathologist and one of the funniest MD stories goes like this. A 17 year old patient I had been working with for three months that suffered a traumatic brain injury, his mother and I were called in to meet with his doctor. This brilliant MD began to explain the nature of my patient's injury and drew diagrams on a dry erase board all the while saying that this is why my patient would never be able to talk again. The three of us listened intently and about 10 minutes into the lecture my patient leaned over to me and asked "What is he talking about ? " Lol !!! The brilliant MD almost jumped out of his pants. I am sorry but in almost 30 years of working in the medical field, I have concluded that in the majority of cases you must be stupid to get into medical school or maybe a memorizing robot !!!