What was dubbed "Sony shock" happened two years ago, when Sony share prices dropped on worse than expected earnings results. Although Sony's profits have since improved, they have not made a dramatic revival.
Analysts also say Sony missed the boat with portable music players by delaying a release of products to play MP3 music files, taking a beating from the iPod by Apple Computer Inc.

Howard Stringer was named Sony's first non-Japanese chairman.
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Movies "Spider-Man" and "Spider-Man 2" have been among the few bright spots in Sony's otherwise faltering performance.
Stringer has overseen the company's entertainment operations, including the recent acquisition of a consortium of U.S. film and television studio Metro-Goldwyn-Mayer MGM.
A native of Cardiff, Wales, Stringer is a former CBS reporter and served as president of the network from 1986 to 1988. He joined Sony in 1997. He was knighted by Queen Elizabeth in 1999.
Idei was a surprise choice as president in 1995, bypassing more than 10 contenders. He was hand-picked by Norio Ohga, who succeeded Sony founder Akio Morita.
In recent years, competition from South Korean rival Samsung Electronics has battered Sony, and Sony has set up a joint venture with Samsung in liquid-crystal displays.
Sony has also fallen behind Japanese rivals such as Sharp Corp. in liquid-crystal display TVs and Matsushita Electric Industrial Co., which makes Panasonic brand products, in the DVD recorder market.