Selling picked up the pace Tuesday as stocks fell to session lows with a little over one hour left in the session. The Nasdaq dropped 1.1%; the S&P 500 lost 0.8% and the Dow Jones industrial average gave up 0.7%. NYSE and Nasdaq volume was tracking about 10%-15% higher than Monday’s light levels. In the stock market today, Athenahealth (ATHN) slumped 13%, fueling a 6% move lower for IBD’s Computer Software-Medical group.