What stonewalling means is that we become so upset by the interaction that we shut down. The listener withdrawals from the interaction, usually out of fear that speaking will make the problem worse. Stonewalling appears to be an attempt to withdraw to calm down or to self-soothe.
The antidote to stonewalling is to take a break from the discussion. As part of Dr. Gottman's research, he asked couples in his love lab to discuss a topic that they experienced conflict about. Then with some of the couples, he told them that the equipment was broken and would they please read some magazines while they fixed the equipment. This gave the couples the opportunity to self-soothe. The couples who took this break in the argument ended up having more productive conflict management discussions than the couples who continued to argue without a break. A good break needs to be at least 20 minutes long, and it needs to focus on soothing without spending the whole time obsessing about the problem. That allows our brain to get out of "fight or flight" and be able to think more clearly, with a better chance of being able to access more of our brain.