U.S. stocks sported slight losses by the middle of the session with trading remaining cautious ahead of the kick-off to the Federal Reserve's annual summit tomorrow. Fed Chair Janet Yellen will give a widely-anticipated speech on Friday. Crude oil extended losses after a weekly reading on U.S. oil inventories showed a far-steeper build than expected. Prices have been buoyed recently over hopes for an OPEC production freeze, a salve to a pick-up in domestic supply. Sales of previously owned homes fell more than expected in July, according to the National Association of Realtors. Tight inventory has chocked some of the demand in recent months and has led to higher prices across the board. Garmin (GRMN) - Get Garmin Ltd. (GRMN) Report fell after being downgraded to SELL from NEUTRAL at Goldman Sachs. Analysts said fitness segment growth is decelerating. TheStreet's Keris Lahiff reports from Wall Street.