Susan Mackie has been teaching the CoRT Thinking tools to some Down's syndrome youngsters. They responded very well. It may be that they have difficulties in setting frameworks for themselves but can respond very well to frames that are provided. Moving from the purely intellectual to the motor area and backagain is an interesting concept.
Some cultures do it while talking.
I am not aware of research on this - though there probably is some. I can see the great value of hand signals both to oneeself and to others.