Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

Investors can expect a positive start to the stock market today, as the Dow Jones Industrial Average (^DJI 0.56%) gained 68 points, or 0.4%, in premarket trading. Global stocks were up in overnight trading, with emerging markets flat, and European stocks higher ahead of a rate-setting meeting of the European Central Bank. Closer to home, investors are looking ahead to tomorrow's jobs report from the U.S. Bureau of Labor Statistics, which is expected to show a gain of 185,000 jobs in January.

Meanwhile, news is breaking this morning on several stocks that could see heavy trading in today's session, including Sony (SONY -0.71%), Costco (COST -0.24%), and General Motors (GM -0.17%).

Sony today said sales of its new PlayStation 4 console helped overall revenue rise by 5% in its fiscal third quarter, to reach $860 million. The Japanese tech giant also booked a profit of $0.22 a share, compared to a loss in the year-ago period. But the biggest news for Sony investors was the company's announcement of a major restructuring plan: Sony is exiting the PC market and spinning off its TV unit in a bid to streamline its business. The company also said that profit for its full fiscal year ending in March will be less than half of what it had projected, due to restructuring charges and weakness in its mobile product division. The stock is down 4.8% in premarket trading.

Costco today booked a solid rise in sales for the month of January. Revenue improved by 6% last month, to nearly $8 billion. Despite cold weather across much of the country and a generally tough selling environment, the megaretailer saw comparable-store sales jump by a healthy 5% in the U.S, and by 6% company-wide. Costco's stock is up 2.5% in premarket trading.

Finally, General Motors announced this morning that fourth-quarter sales increased by 3%, to $40.5 billion, slightly below the $41 billion that Wall Street had expected. Adjusted profit was $0.67 a share, also lower than the $0.88 that analysts were targeting. CEO Mary Barra said the automaker is entering 2014 in "execution mode" after a year of tough decisions that have helped shore up the balance sheet and strengthen GM's product portfolio. The stock is down 3.7% in premarket trading.