Try this. Sit down with your newspaper. Have a waste basket two metres away. Read your newspaper from the middle outwards. As you finish each double page spread screw it up into a ball and throw it carefully at the waste basket. (How many times did you score a hit? If the answer is none I am sorry; this technique may not be for you.)

         To hit the basket with the balls of newspaper you throw with the muscles of your arm. When you throw a glance at something you throw with the muscles of your eyes. To see 3D, stereo-pair, pictures, throw with the muscles of your eyes in a way slightly different from the usual.

         It is very complicated just to throw an ordinary glance. Each of your two eyes has to be pointed at the object, and each eye has to be focused on the object. Four different functions are coordinated. We normally get so good at this kind of throwing that we can switch glances instantly, and follow moving objects. The brain co-ordinates the muscles and locks on with ease.

It takes me roughly half a second to switch attention between two objects like these

The complexity and the speed with which eyes and brain operate are remarkable (see the book Eye and Brain, The Psychology of Seeing, by R. L. Gregory, Oxford University Press, 1998). The brain makes use of previous experience in its operations, learns what to expect, and catches on.

         Seeing a stereo-pair involves brain activity similar to that of ordinary vision, but the functions of pointing and focusing are concentrated on the each of the two members of the stereo-pair, one for each eye. The brain finds the appropriate muscular adjustments and locks on. This is well within the scope of normal seeing. Only in cases of amblyopia will there be difficulty. Acquisition of a new conditioned reflex, a mental accomplishment, is all that is necessary, rather like learning to ride a bicycle. Good muscular coordination is obviously helpful, and one would expect aviators, motorcyclists, dancers and ping-pong players to catch on faster than the rest of us.

[In the carefully prepared presentation of their stereo camera, Fujifilm present the following Caution: Using the FinePix REAL 3D W1: -
2D display is recommended for young children (up to the age of about six) whose visual system is still maturing and for individuals with notable differences in vision between their two eyes, who may find it difficult or impossible to observe the 3D effect. Should you experience fatigue or discomfort while viewing 3D images, cease use immediately. A ten-minute break is recommended about once every half hour. Switch to 2D immediately if 3D images still appear double after you have adjusted parallax. Individuals with a history of photosensitive epilepsy or heart disease or who are unwell or suffering from fatigue, insomnia, or the effects of alcohol should refrain from viewing 3D images. Viewing 3D images while in motion may cause fatigue or discomfort.]