Single Image Random Dot Stereograms (SIRDS):

Why do they work, and what do they teach us about Perception?

Random Dot Stereograms are everywhere on the Web!

Single Image Random Dot Stereograms (SIRDS) are not only a lot of fun, but they demonstrate many of the properties of stereopsis. "Stereopsis" means that each eye sees a slightly different image, which is essential for our perception of depth.

Leonardo da Vinci demonstrated in his writings that he understood stereopsis, but the 19th century British physicist Charles Wheatstone is usually credited with its first clear demonstration. Wheatstone invented a stereoscope, a device which presented the first stereograms.

Bela Julesz (1971) was the first to demonstrate that depth can be perceived from stereograms that do not contain recognizable objects. These were the first "random dot stereograms."

The 1980's and 1990's experienced a boom in recreational SIRDS watching.

SIRDS Facts:

• Four month old human infants can see depth in stereograms.
• Stereopsis is not restricted to humans: Monkeys, cats, and falcons show evidence of perceiving depth in stereograms.
• Viewing SIRDS is a learned skill. The process can't be hurried up by telling a person what objects to look for. Once the skill has been mastered, it's difficult to avoid seeing the images.
• Stereopsis can be used to detect counterfeit bills and camouflaged objects.
• Don't feel badly if you can't see SIRDS images. Approximately 5-10% of the population is "stereoblind."

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Laura Freberg

Cal Poly Home Page

Psy/HD

updated 7/20/98