Monday, September 28, 2009

Retinal Image Inversion

In order to see the objects that surround us the brain must process the information it receives from the retina. As light bounces off objects the lenses of our eyes detect changes and focus the imagery we see onto our retinas. As a result of passing through the lens, this image is inverted. The brain reorients the image so it can be perceived in a way we would describe as “normal”. There really is no upright on out retinas its all based upon our experience. As we move around we learn what upright is. But what if the image received by the lens were inverted before it hit the retina? Would it then be flipped so an upright image was projected onto the retina? If so, would we see the world upside down? Does the retinal image have to be inverted for us to see something upright?

George Stratton was the first to address these concerns. In his 19th century experiment “Vision without inversion of the retinal image”, he built a set of goggles out of 2 double convex lenses. This would provide the retina with a previously inverted image. When the subject initially wears the glasses, he is disoriented. The world he sees is upside down. Physical movement is very difficult if the wearer relies solely on the visual image. If the wearer places his hands out in front of him, they seem to come from above. Stratton claimed that with time, the wearer adapted to the goggles and experienced the world in an upright state.

Some researchers dispute this claim. They believe that with adaptation, it is not that our vision appears upright again, but that because we’ve experienced the world in an upright manner and learned spatial clues over time, we can interpret the visual image we see while wearing the goggles. If this is so, it comes as a result of perceptual constancy. As in the dragon illusion I posted earlier, the impressions we receive from objects are what we assume them to be, and are not a direct representation of the stimulus presented. We maintain these constancies even when the stimuli is changing, which could explain why new researchers debate Stratton’s findings.

In the video below, the subjects vision isn’t inverted vertically, but the goggles reverse the left and right fields of vision. Notice how the subject struggles to make sense of this new world.


2 comments:

Anonymous said...

wheres the video!!!???

Rex said...

The video does not work for me either, but this video is relevant and shows the inversion goggles being used for experiments:

http://video.google.com/videoplay?docid=2048269788799603527#