If you take a broken pair of sunglasses, or break a really cheap pair, so that only one eye sees darkened light, then your brain can perform amazing and apparently unrelated tricks. Yes, I'm going to talk about optical illusions on radio. You can try these at home.
In 1922, German physicist Carl Pulfrich observed that when a pendulum is moving in a straight line backwards and forwards in front of you;if you don't fall asleep, that when you have one eye looking through a grey lens and the other eye clear, then the pendulum looks as if its moving in a big stretched circle. The two dimensional flat line of its path looks as if its moving in a three dimensional ellipse, going away from you and then towards you as it goes from left to right, or right to left, depending on which eye is looking through the dark lens. Pulfrich happened to try this because of an eye injury that caused a cataract in his eye. The theory is that the nerve cells in the visual cortex receiving the brighter image, actually process the image faster than the neurons processing the darker image. This separation in time causes a spatial illusion, because your brain integrates the two images as if they were slightly separated in space. So you get your view master stereoscopic 3-D effect, with only one image, and no messing around with polarized lenses or red/green glasses.
Flash forward to the 1990's and people realized that fun could be had with this illusion on TV, wherever there is side to side movement, such as sporting events, parades, and action movies, and of course, video games. When the movement stops, the 3-D illusion goes away. A special Doctor Who episode called "Dimensions In Time" was produced especially to exploit the Pulfrich 3-D effect, and featured a cross-over with the soap opera "East-enders". The BBC produced several 3-D TV shows to raise money for the "Children in Need" charity in 1993, selling the Pulfrich half-sunglasses.. In America, an episode of "Third Rock from the Sun" was made in 3-D, and an episode of "Married with Children". In fact, you don't even need a show with horizontal action, if you tune in to a dead channel and look at the TV "snow" while wearing the half sunglasses, then you will see the static of random dots boiling around in a big 3-D cylinder.
Old arcade games like R-type and Nemesis give a good 3-D illusion when viewed through Pulfrich half-sunglasses.
I took my Pulfrich half-sunglasses to a twenty-four hour science fiction movie festival in Melbourne many years ago, and had fun with the movies going into three dimensions whenever there was horizontal action. Then I had the surprize of seeing a movie where it STAYED in 3-D for the whole movie, even in the scenes without camera movement or horizontal action. I realized that the movie had originally been filmed in stereo with two cameras for viewing in special cinemas with red/green stereo glasses or glasses with differently polarized lenses. The cinema I was in, was only showing the view from one camera, through one projector. With the half lenses on, somehow my brain was producing a stereographic three dimensional illusion. I passed the glasses around the group of twenty friends, and they all saw the same illusion; it wasn't just me. Since that time I've tested the effect on other movies originally filmed with two cameras, and then only shown on one projector, and it works for them. It seemed to be more effective in a theatre than for the same film shown on TV. My friend Matthew dubbed it the "Woolf-Pulfrich effect" in my honour. Since that time, I haven't found any references to any prior claims. When I asked computer scientists who research screen optical illusions at the University of Technology, Sydney about just how and why the "Woolf-Pulfrich effect" works, they just refused to believe me.
Try it yourself with Alfred Hitchcock's "Dial M for Murder" which was originally shot in 3-D but is usually screened in two-dee, and be a real scientist! But beware if your emotional point of view changes during the experiment. If you find yourself feeling anxious or depressed, then take off the half-sunglasses and change the lens to the other side, and you'll feel better.
In a bizarre twist, Harvard Psychiatrist Dr Fredric Schiffer, is using half-sunglasses, as a form of diagnosis and treatment for some types of anxiety and depression disorders. Some patients have their anxiety and depression intensified when one lens is dark, and lifted when the other view is darkened instead. It seems that one half of their brain has an optimistic view, and the other has a more dismal view. He's found that patients who respond to the half-sunglasses are good candidates for Transcranial Magnetic stimulation, a treatment that stimulates the healthy hemisphere of the brain with super-strong electro-magnets. Sixty per cent of depressed patients felt better when their right eye saw the brighter image, causing their left brain to be stimulated. It wasn't reported if they enjoyed any 3-D effect under magnetic stimulation.
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