NEW YORK — The U.S. stock market is slightly higher in midday trading as investors respond to encouraging results from several retailers.J.C. Penney and Best Buy rose sharply after improving their performance in the latest quarter. Sears Holdings also rose.The Standard & Poor's 500 index increased three points, or 0.2 percent, to 1,848 as of noon Eastern time Thursday.The Dow Jones industrial average rose 37 points, or 0.2 percent, to 16,235. The Nasdaq climbed 11 points, or 0.3 percent, to 4,303.J.C. Penney surged 24 percent after the department store chain swung to a small profit in the latest quarter following a massive loss in the same period a year earlier.Best Buy climbed 5 percent after it also returned to profitability in the fourth quarter.