Watch Art Cashin: S&P testing this key support level

Art Cashin says investors should keep an eye on a key support level for the S&P 500 stock index that's already been tested several times today.

Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday that if the S&P goes below the 1693-1695 area, it would be breaking through the "neckline of a head and shoulders" pattern, a bearish sign.

"So far, tested successfully. We'll see how long they can keep it up."