Not sure the semantics of whether stuttering is neurological or X or Y or Z is useful - as long as you understand and accept why hard, silent blocks are the more progressed version of repetitions/prolongations. Blocks are more impactful both the speaker and listener. If you t-t-t-talk like this, your listener probably knows what the issue is. If you just. Pause. Silently. *eye squint, hand flap etc* Your listener is likely to have no clue what is going on.