HFTs - Are They Automated or Voice Traders?

When you start to get automated traders in the market, what seems to happen is that in normal times, the markets are very efficient and liquid. But then you get these pockets where you get kind of flash crash dynamics when suddenly there's about illiquidity which is really, really bad. When you have voice traders, you get less of that. So with voice traders, I find that you get in normal times slightly less efficient markets than automated trading but in crazy times, voice traders step up and stabilize the market somewhat. As a broader research matter, there are several papers that do the fact that the environment in which we often find ourselves today, more conducive for human beings rather than machines?