Three-Dimensional （3D） movies have been becoming more and more popular in recent years．It seems 3D TV sets may be going into family households in the near future．While new digital 3D technology has made the experience more comfortable for many, for some with eye problems, long 3D viewing may result in an aching head, doctors say．  "There are a lot of people walking around with very minor eye problems, which under normal situations, the brain deals with naturally," said Dr Michael Rosenberg, an ophthalmologist （眼科医师） in Chicago．He said in a 3D movie, these people face a completely new sensory experience．"That translates into greater mental effort, making it easier to get a headache," Rosenberg told Reuters． In normal vision, each eye sees things at a slightly different angle．"When that gets processed in the brain, that creates the perception （感觉） of depth," said Dr Deborah Friedman, an ophthalmologist in New York．The images people see in three dimensions in the movies are not calibrated （校准的） in the same way that their eyes and brain are．"If your eyes are a little off to begin with, then it's really throwing a whole degree of effort that your brain now needs to exert （竭尽全力）," he said． Dr John Hagan, a Kansas City ophthalmologist, said some people who do not have normal depth perception cannot see in 3D at all．He said people with eye muscle problems, in which the eyes are not pointed at the same object, have trouble processing 3D images． Rock Heineman, a spokesman for RealD, a provider of 3D equipment to theaters, said headaches and nausea were the main reasons 3D technology never took off． Heineman said older 3D technology used two film projectors（放映机）, one that projected a left-eye image and one that projected a right-eye image．Three-D glasses would allow viewers to see a different image in each eye． "People often complained of headaches and it was really because the projectors weren’t lined up," Heineman said． Now his company has developed a new single digital projector, which switches between the left and the right-eye image 144 times a second, to help overcome some of the old problems． "By going to a single digital proj  ector, those problems were solved," he said．Friedman said he thinks most people will do fine with 3D movies and with 3D TVs, but Rosenberg said people may quickly tire of the novelty （新鲜事物）．"I suspect there will be a lot of people who say it's sort of neat, but it's not really comfortable," he said．小题1:The text is mainly about ____．
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