Steven Pinker -- How the Mind Works - Hampshire High Italian ...

224 I HOW THE MIND WORKSconcerting effect called binocular rivalry. You can experience a mildercase by holding a finger a few inches in front of you with both eyes opengazing into the distance so you get a double image. If you pay attention toone of the double images, you will notice that portions slowly becomeopaque, dissolve into transparency, fill in again, and so on.A better kind of anaglyph puts polarizing filters, rather than coloredfilters, over two projector lenses and in the cardboard glasses. The imageintended for the left eye is projected from the left projector in lightwaves that oscillate in a diagonal plane, like this: /. The light can passthrough a filter in front of the left eye which has microscopic slits thatare also in that orientation, but cannot pass through a filter in frontof the right eye with slits in the opposite orientation, like this: \. Conversely,the filter in front of the right eye allows in only the light comingfrom the right projector. The superimposed images can be in color, andthey do not incite rivalry between the eyes. The technique was used toexcellent effect by Alfred Hitchcock in Dial "M" for Murder in the scenein which Grace Kelly reaches out for the scissors to stab her would-bestrangler. The same cannot be said for the film adaptation of ColePorter's Kiss Me Kate, in which a dancer belts out "Too Darn Hot" on acoffee table while flinging scarves at the camera.Modern anaglyph glasses have panes made of liquid crystal displays(like the numbers on a digital watch) which act as silent, electrically controlledshutters. At any moment one shutter is transparent and the otheris opaque, forcing the eyes to take turns at seeing a computer screen infront of them. The glasses are synchronized with the screen, whichshows the left eye's image while the left shutter is open and the righteye's image while the right shutter is open. The views alternate tooquickly for the eyes to notice the flicker. The technology is used in somevirtual reality displays. But the state of the art in virtual reality is a hightechversion of the Victorian stereoscope. A computer displays eachimage on a little LCD screen with a lens in front of it, mounted in frontof each eye on the inside of a helmet or visor.These technologies all force the viewer to don or peer through somekind of apparatus. The illusionist's dream is a stereogram that can beseen with the naked eye—an autostereogram.