American Scientist

To the Editors:

I read with great pleasure the Computing Science column “Flights of Fancy” (January–February) by Brian Hayes about efforts to decipher how flocking birds coordinate their movements. The STARFLAG group’s attempts to identify individual birds in multiple photographs of one flock reminded me of an experiment I tried in 1992 involving human perception and high-speed stereoscopic correlations. I was developing a product called Stereoscopic Showcase that allowed personal computer users to see images on computer monitors stereoscopically, using inexpensive field-sequential liquid crystal display shutter glasses. I wanted to include some 3D images and because computer monitors allowed continuous changes in images, I could create a “dynamic random-dot stereogram,” meaning dots defining 3D objects shifted in frame after frame.

We electronically mimicked taking an object, say a book, and spraying it with random white luminescent paint dots and then making stereoscopic photographs of the book. We removed the “paint,” sprayed it randomly again and again and took many more photographs. In time, we had sequences of images of each object. I displayed the successive frames of the image on the monitor at between 15 and 20 frames per second. One image was similar to a ripple spreading over a pond, as seen from above; the other was a helically rising surface, again seen from above.

I feared viewers might have a hard time correlating the thousands of dots in the left eye with those in the right during the brief displays. But I was astonished by how quickly people processed the correlations and saw the objects clearly. I remain amazed at our visual apparatus’s ability to find matches among thousands of ever-changing, indistinguishable points.

Peter Brooks
Stuyvesant High School