How long has 3-D technology been around? Most of us might think of crowds of teenagers in a 1950's movie house watching Bwana Devil in 3-D. But 3-D technology made its first appearance on the scene in 1838 with the first stereoscope . And the first actual 3-D movie was a 1903 film called Le Ariveed'un Train. Although it has such a long history, the technology has still remained based on one simple principle-----to make 3-D effects you must find a way to project two slightly different pictures to each eye. Modern 3-D technology works by rapidly flickering  two versions of the movie and projecting them onto each eye. The brain does the rest of the work, combining the two pictures together into one and giving the show the appearance of depth, the third dimension. But does this exposure, especially long exposures, cause harm to the child's developing brain and visual system? Unfortunately, long-term studies on new flicker digital 3-D technology and children aren't yet available. We do not know if regular or daily 3-D viewing over years affects the developing visual system, although older 3-D methods basically do the same thing and are not considered harmful. The question of possible harm in modern 3-D use in TV is really based on two facts: the amount of time children will now be watching 3-D TV each day and the sensitivity some children show in reaction to 3-D viewing. It is difficult to make actual lab studies of longer term 3-D viewing in children because of the possible harm of the experiment. Researchers will have to wait until 3-D TV technology is already in the marketplace for a number of years, then check heavy 3-D TV watchers and compare them with non-watchers. With a 3-D television technology in the home, we will soon be able to answer the question of whether or not longer and more frequent periods of 3-D exposure cause more changes in the visual system. We may find that the bigger problem is the introduction of a new technology that leads to even more time spent on TV rather than playing outdoors. The author's purpose in writing the text is to   _
ask children not to watch 3-D movies discuss if 3-D viewing is harmful to children. introduce the advantages of 3-D technology. predict the development of 3-D technology.