Why the correction? Machines have taken over

The global factors behind Friday's big selloff

In days of old, a Wall Street blowout like Friday's would have featured harried traders shouting out sell orders on exchange floors, trying to limit their losses as the market crumbled.

The new market age is decidedly different: Rather than that seething cacophony, aggressive corrections like the current ones are directed by a faceless metronome of computer-generated orders, triggering irresistible momentum and trillions in losses.

Amid it all, market veterans are left to ponder when the script will flip and market direction will turn not by newfound optimism among traders in the pits, but rather by algorithms that generate "buy" rather than "sell" signals.

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"It feels like sell program after sell program," said Michael Cohn, chief market strategist at Atlantis Asset Management, a boutique firm in New York. "It seems to happen first thing in the morning, and then however the market transpires during the day is how they close it. If it looks like it's coming back, they'll take it at the end. If if looks like it's heading lower, they'll slam it at the end of the day."

It's no secret that humans are having increasingly less influence on the markets generally. But traders feel the machines are having an outsized influence during the most recent slide, which has sent the major U.S. averages into correction territory.

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