Marketplace Tech continues our Wall Street technology series with a look at high-frequency trading, where powerful computers can make hundreds of thousands of trades in milliseconds, making big money off tiny stock price differences. Dave Lauer is a former high-frequency trader, but he's now a critic of the business. He explains why to Marketplace Tech guest host Mark Garrison. Click the audio player above to listen to the interview.

Follow Mark Garrison at @GarrisonMark