I have a question as a complete outsider: how much of what's happening is being driven directly by human-driven transaction and how much is automated computer-d

I have a question as a complete outsider: how much of what's happening is being driven directly by human-driven transaction and how much is automated computer-driven trading? (Yes, I understand these are hazy terms.) And, perhaps more fundamentally: how much of market volatility is the consequence of automated decision making? It seems, again naivete is at play here, but it seems like that could be a pretty unstable system. I guess I think of it like this: the U.S. utilizes Permissive Action Links and other security measures to provide for launch security. Given the centrality of the economy (though not wanting to overstate it), it seems like a large-scale mistake in some models could cause misfiring in ways we wouldn't want but that a human agent could (theoretically) prevent.